From a4c85dec55394fe3ef6005acff6a66b7fbfc464a Mon Sep 17 00:00:00 2001
From: Valera V Harseko <vharseko@3a-systems.ru>
Date: Tue, 01 Sep 2026 18:18:00 +0000
Subject: [PATCH] Merge remote-tracking branch 'origin/master' into issues/903-jdbc-deadlock-retry-window

---
 opendj-server-legacy/src/main/java/org/opends/server/backends/pluggable/VLVIndex.java                     |   23 
 opendj-server-legacy/src/test/java/org/opends/server/backends/jdbc/TestCase.java                          |  117 +
 opendj-server-legacy/src/test/java/org/opends/server/backends/jdbc/CachedConnectionTestCase.java          | 1870 +++++++++++++++++++++++
 opendj-server-legacy/src/main/java/org/opends/server/backends/jdbc/CachedConnection.java                  | 1363 ++++++++++++++++
 opendj-server-legacy/src/test/java/org/opends/server/backends/jdbc/JDBCStorageRetryTest.java              |  776 +++++++++
 opendj-server-legacy/src/test/java/org/opends/server/backends/pluggable/PluggableBackendImplTestCase.java |   34 
 opendj-server-legacy/src/main/java/org/opends/server/backends/jdbc/JDBCStorage.java                       |  585 ++++++-
 opendj-server-legacy/src/test/java/org/opends/server/backends/jdbc/StampConnectionTestCase.java           |   16 
 8 files changed, 4,628 insertions(+), 156 deletions(-)

diff --git a/opendj-server-legacy/src/main/java/org/opends/server/backends/jdbc/CachedConnection.java b/opendj-server-legacy/src/main/java/org/opends/server/backends/jdbc/CachedConnection.java
index 188f7ba..22d63d4 100644
--- a/opendj-server-legacy/src/main/java/org/opends/server/backends/jdbc/CachedConnection.java
+++ b/opendj-server-legacy/src/main/java/org/opends/server/backends/jdbc/CachedConnection.java
@@ -23,21 +23,169 @@
 
 import java.sql.*;
 import java.time.Duration;
+import java.util.ArrayDeque;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.Deque;
+import java.util.HashSet;
+import java.util.IdentityHashMap;
+import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Properties;
+import java.util.Set;
 import java.util.concurrent.*;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 public class CachedConnection implements Connection {
     private static final LocalizedLogger logger = LocalizedLogger.getLoggerForThisClass();
 
+    // What has been reported once already. Every one of these reports a setting rather than an
+    // event - a property that is not a number, a url no bound of this class can reach, a driver
+    // whose property names are not known here - so it does not become truer by being repeated,
+    // and every operation of the backend comes through here.
+    // Declared above every field whose initializer can reach warnOnce(): class variable
+    // initializers run in textual order (JLS 12.4.2), so a set declared below aliveBypassNanos
+    // would still be null the moment a property this class reports on carries a value worth
+    // warning about - a window longer than the ttl, or one that is not a number - and the report
+    // would leave the class uninitializable rather than merely configured oddly.
+    static final Set<String> warnedOnce = ConcurrentHashMap.newKeySet();
+
     static final String TTL_PROPERTY = "org.openidentityplatform.opendj.jdbc.ttl";
     static final long DEFAULT_TTL_MS = 15000;
 
+    /**
+     * How long a pooled connection is handed out without being validated after it was last proven
+     * alive, in ms; 0 validates every borrow, the way this pool did before the window existed.
+     * <p>
+     * The validation of a connection is a round trip of its own - an empty query on postgresql, a
+     * ping on mysql, a round trip of its own on oracle and sql server - and every operation of
+     * this backend pays it next to the single statement the operation came for. It earns that on a
+     * connection that has been sitting in the pool, which the database or a firewall may have
+     * dropped in the meantime; it earns nothing on one that answered a moment ago, which is most
+     * of them under load. So a connection proven alive within this window is trusted rather than
+     * validated, the way the aliveBypassWindow of HikariCP does it.
+     */
+    static final String ALIVE_BYPASS_PROPERTY = "org.openidentityplatform.opendj.jdbc.alive.bypass";
+    static final long DEFAULT_ALIVE_BYPASS_MS = 500;
+
+    /**
+     * The longest window this class uses, whatever {@value #ALIVE_BYPASS_PROPERTY} and the
+     * {@value #TTL_PROPERTY} it is clamped to say. The clamp to the ttl alone does not bound it:
+     * the ttl has no upper bound of its own, and with both set high enough the conversion to
+     * nanoseconds saturates - the window then outlasts every reading it is compared against, and
+     * no connection of the pool is ever validated again. An hour is already far past what this
+     * window is about, which is a connection that answered a moment ago.
+     * <p>
+     * A compile-time constant, so that it holds its value wherever it is read from: the initializer
+     * of {@link #aliveBypassNanos} reaches it, and a field initialized in declaration order would
+     * still be 0 there if it were ever moved below (JLS 12.4.2).
+     */
+    static final long MAX_ALIVE_BYPASS_MS = 60 * 60 * 1000L;
+
+    // Read once, at class initialization: every operation of this backend borrows a connection,
+    // and the borrow is not the place to parse a system property. Not final so that a test can
+    // vary the window without a class loader of its own, and volatile because a non-final static
+    // long is written neither atomically nor visibly to the threads reading it (JLS 17.7) - every
+    // worker of the backend and every replay thread reads this one.
+    static volatile long aliveBypassNanos = TimeUnit.MILLISECONDS.toNanos(getAliveBypassMillis());
+
+    /**
+     * Bounds the connect and the login of one attempt to establish a connection, in seconds; 0 for
+     * no bound of its own - the deadline of {@value #POOL_TIMEOUT_PROPERTY} still bounds the
+     * attempt, since it stands for the whole borrow. Setting both to 0 is what leaves a connect
+     * unbounded.
+     */
+    static final String CONNECT_TIMEOUT_PROPERTY = "org.openidentityplatform.opendj.jdbc.connect.timeout";
+    static final long DEFAULT_CONNECT_TIMEOUT_SECONDS = 30;
+
+    /**
+     * Bounds a whole borrow - every connect attempt and every wait for a pooled connection - in
+     * seconds; 0 for no bound. Not to the millisecond: the connection in hand is validated
+     * whatever the deadline says, and an attempt is never given less than a second, so a borrow
+     * can return a validation and a last attempt past it.
+     */
+    static final String POOL_TIMEOUT_PROPERTY = "org.openidentityplatform.opendj.jdbc.pool.timeout";
+    static final long DEFAULT_POOL_TIMEOUT_SECONDS = 60;
+
+    /** Bound of the validation of a pooled connection: isValid(0) means "no timeout" in the JDBC contract. */
+    static final int VALIDATION_TIMEOUT_SECONDS = 5;
+
+    /** 08001, sqlclient_unable_to_establish_sqlconnection: the state of a connect that did not happen. */
+    private static final String CONNECT_FAILED_SQL_STATE = "08001";
+    /** 53300, too_many_connections: how the standard - and postgresql - reports a server taking no further connection. */
+    private static final String CONNECTION_LIMIT_SQL_STATE = "53300";
+    /** 57P03, cannot_connect_now: postgresql starting up, shutting down or in recovery. */
+    private static final String NOT_ACCEPTING_YET_SQL_STATE = "57P03";
+
+    static final long MAX_BACKOFF_MS = 1000;
+    static final long STALL_WARNING_AFTER_MS = 1000;
+    static final long STALL_WARNING_INTERVAL_MS = 10000;
+
+    /** How many links of the cause and getNextException() chains of a failure are looked at. */
+    private static final int MAX_CHAIN_LENGTH = 32;
+
+    /** What a connection string is cut down to where this cannot tell its credentials from the rest of it. */
+    static final String CREDENTIALS_HIDDEN = "<credentials hidden>";
+    /**
+     * A password standing where neither the userinfo nor the parameters of a url are looked for.
+     * The name goes by more than one spelling: mysql numbers the factors of a multi-factor login
+     * (password1, password2), and a wallet or a key store carries one under a name of its own
+     * (oracle.net.wallet_password, javax.net.ssl.keyStorePassword).
+     * The value of one ends at a separator of a connection string or at the first space: a driver
+     * is free to name a parameter in the middle of a sentence ("password=hunter2 for user u at
+     * h:5432"), and a value class running to the end of the string would take the host, the port
+     * and the cause of the failure into the blank along with the password.
+     */
+    private static final Pattern SECRET_PARAMETER =
+        Pattern.compile("(?i)([\\w.]*(password|passwd|pwd)\\d*)\\s*=([^\\s,)&;?]*)");
+
+    /** The parameters of a connection string worth keeping in a message: which database, not who connects. */
+    private static final Set<String> IDENTIFYING_PARAMETERS = Collections.unmodifiableSet(new HashSet<>(
+        Arrays.asList("databasename", "database", "instancename", "currentschema", "servicename")));
+
+    // setNetworkTimeout() takes the executor its timeout handling runs on: the drivers it is used
+    // with here only set a socket option in it, so it costs a call rather than a thread.
+    private static final Executor DIRECT_EXECUTOR = Runnable::run;
+
+    // Throttled per connection string: two JDBC backends stalling at once have a stall of their
+    // own to report, and a single timestamp would let one of them starve the other. Keyed by the
+    // safe form of it, the way warnedOnce below is: a static field of this class outlives every
+    // borrow, and the password of the backend has no business in one.
+    private static final Map<String, AtomicLong> lastStallWarning = new ConcurrentHashMap<>();
+    private static final AtomicLong lastReadBoundWarning = new AtomicLong();
+
+    /**
+     * When an operation last reported that the database had dropped a connection of a pool, as a
+     * {@link System#nanoTime()} reading per connection string. A connection proven alive before
+     * that moment is validated on its next borrow whatever the window says: whatever dropped one
+     * connection - a restart, a failover, a network that went away - dropped every connection
+     * established before it, and the window would otherwise hand out the rest of that generation
+     * one by one until the pool runs out of them. It is set by the caller that saw the failure
+     * ({@code JDBCStorage}), never by a validation that failed here: an idle connection the server
+     * reaped is a routine event, and it says nothing about the connection in use that the pool is
+     * about to hand out.
+     */
+    private static final Map<String, Long> poolDistrustedAt = new ConcurrentHashMap<>();
+
     final Connection parent;
 
-    static LoadingCache<String, BlockingQueue<CachedConnection>> cached = Caffeine.newBuilder()
+    // A deque handed out from the end it is returned to: the connection borrowed next is the one
+    // returned last, so under any load the pool keeps reusing its hottest connections instead of
+    // walking round every one it ever opened. That is what gives the window above anything to
+    // bypass - a connection reached only after a whole cycle of the pool has been idle far longer
+    // than the window - and it leaves the connections nothing needs at the cold end of the deque,
+    // where the per-connection idle expiry of #878 can find them. Until that lands, the cold end
+    // is reached only when the whole pool expires, after DEFAULT_TTL_MS with the backend idle.
+    // A deque takes one lock for both of its ends where the queue it replaces took one for each,
+    // so a borrow and a return no longer proceed side by side - against the round trip the window
+    // above saves, and the connect the reuse saves, that lock is not worth a FIFO handoff.
+    static LoadingCache<String, BlockingDeque<CachedConnection>> cached = Caffeine.newBuilder()
         .expireAfterAccess(Duration.ofMillis(getCacheTtlMillis()))
-        .removalListener((String key, BlockingQueue<CachedConnection> value, RemovalCause cause) -> {
+        .removalListener((String key, BlockingDeque<CachedConnection> value, RemovalCause cause) -> {
             for (CachedConnection con : value) {
                 try {
                     if (!con.isClosed()) {
@@ -48,66 +196,1198 @@
                 }
             }
         })
-        .build(conStr -> new LinkedBlockingQueue<>());
+        .build(conStr -> new LinkedBlockingDeque<>());
 
     /**
      * Returns the time after which an idle pooled connection is closed, as configured by the
      * {@value #TTL_PROPERTY} system property. An invalid value is ignored in favor of the default.
      */
     private static long getCacheTtlMillis() {
-        final String ttl = System.getProperty(TTL_PROPERTY);
-        if (ttl != null) {
+        return getNonNegativeProperty(TTL_PROPERTY, DEFAULT_TTL_MS, "ms");
+    }
+
+    /**
+     * Returns the alive window, clamped to the {@value #TTL_PROPERTY} an idle pooled connection is
+     * kept for and to {@link #MAX_ALIVE_BYPASS_MS} behind it. A window longer than the ttl is one
+     * the pool cannot back: it goes on trusting the last answer of a connection past the point the
+     * pool would have closed and replaced it, which is a claim about a connection that is no longer
+     * there. The ttl has no upper bound of its own, though, so the second clamp is what keeps a
+     * value the unit conversion saturates on from leaving every connection of the pool trusted for
+     * the life of the server.
+     * <p>
+     * Read at class initialization, like the ttl it is clamped to, so a value set after that
+     * changes neither.
+     */
+    static long getAliveBypassMillis() {
+        long configured = getNonNegativeProperty(ALIVE_BYPASS_PROPERTY, DEFAULT_ALIVE_BYPASS_MS, "ms");
+        final long ttl = getCacheTtlMillis();
+        if (configured > ttl) {
+            warnOnce(ALIVE_BYPASS_PROPERTY + "=" + configured + ">" + ttl,
+                "The %s window of %d ms is longer than the %d ms of %s a pooled connection is kept for,"
+                    + " and is used as %d ms: a connection trusted for longer than the pool keeps it would"
+                    + " be trusted past the point the pool closed it",
+                ALIVE_BYPASS_PROPERTY, configured, ttl, TTL_PROPERTY, ttl);
+            configured = ttl;
+        }
+        if (configured > MAX_ALIVE_BYPASS_MS) { // the ttl it was just clamped to has no upper bound of its own
+            warnOnce(ALIVE_BYPASS_PROPERTY + ">" + MAX_ALIVE_BYPASS_MS,
+                "The %s window of %d ms is longer than the %d ms this pool trusts a connection for at most,"
+                    + " and is used as %d ms: a longer one saturates the arithmetic it is compared in and"
+                    + " leaves every connection of the pool trusted for the life of the server",
+                ALIVE_BYPASS_PROPERTY, configured, MAX_ALIVE_BYPASS_MS, MAX_ALIVE_BYPASS_MS);
+            return MAX_ALIVE_BYPASS_MS;
+        }
+        return configured;
+    }
+
+    /**
+     * Returns the value of a numeric system property, ignoring a value that is not a non-negative
+     * number in favor of the default. The unit is the one the property is read in, so that the
+     * value the message names is not mistaken for another.
+     */
+    private static long getNonNegativeProperty(String name, long defaultValue, String unit) {
+        final String value = System.getProperty(name);
+        if (value != null) {
             try {
-                final long millis = Long.parseLong(ttl.trim());
-                if (millis >= 0) {
-                    return millis;
+                final long parsed = Long.parseLong(value.trim());
+                if (parsed >= 0) {
+                    return parsed;
                 }
             } catch (NumberFormatException ignored) {
             }
-            logger.warn(LocalizableMessage.raw("Ignoring invalid value \"%s\" of the %s property, using %d ms",
-                ttl, TTL_PROPERTY, DEFAULT_TTL_MS));
+            // reported once for this value: both properties are read on every borrow, so a
+            // "30s" of a typo would otherwise put two lines in the log per backend operation
+            warnOnce(name + "=" + value, "Ignoring invalid value \"%s\" of the %s property, using %d %s",
+                value, name, defaultValue, unit);
         }
-        return DEFAULT_TTL_MS;
+        return defaultValue;
+    }
+
+    /** Reports something about a setting once for the life of the jvm, however many borrows meet it. */
+    private static void warnOnce(String key, String format, Object... args) {
+        if (warnedOnce.add(key)) {
+            logger.warn(LocalizableMessage.raw(format, args));
+        }
+    }
+
+    /**
+     * The drivers this backend is used with, recognized by the prefix of the connection string,
+     * together with the properties that bound one attempt to establish a connection. Not one of
+     * them bounds the attempt with a single property: the one named first covers the socket
+     * connect, and the login behind it - the reads of the prelogin handshake, of TLS and of
+     * authentication, the phase a proxy at its connection limit or a moved VIP leaves unanswered -
+     * needs the read bound behind it. That holds for the SQL Server driver too, whose loginTimeout
+     * leaves the read of the prelogin answer unbounded - and for pgjdbc, whose loginTimeout is not
+     * a bound of the socket at all: Driver.connect hands the login to a daemon thread of its own
+     * and abandons it at the timeout, so an unbounded read there leaks a thread and a socket per
+     * borrow instead of failing one (CachedConnectionTestCase covers every one of them against a
+     * socket that never answers).
+     */
+    enum ConnectDialect {
+        /**
+         * postgresql: every property of the three takes seconds. connectTimeout covers the socket
+         * connect and socketTimeout the reads of the login: pgjdbc puts an SO_TIMEOUT on the login
+         * socket only where socketTimeout is set (ConnectionFactoryImpl.tryConnect, both before and
+         * after enableSSL), and it defaults to none. loginTimeout is kept on top of the two for a
+         * url naming more than one host, where each of them costs a login of its own - the connect
+         * is one budget for all of them, taken from the single System.nanoTime() in front of the
+         * loop over the hosts - but it is not a bound this class could rely on alone: Driver.connect
+         * runs the login on a daemon thread, gives up on the thread rather than on the login, and
+         * the thread stays parked in the read for as long as the read lasts.
+         */
+        POSTGRES("jdbc:postgresql:", '?',
+            new String[]{"connectTimeout", "loginTimeout"}, 1, 0,
+            new String[]{"socketTimeout"}, 1, true,
+            new int[]{}, new int[]{}),
+        /** mysql: both properties take milliseconds; socketTimeout is a socket read timeout that outlives the login. */
+        MYSQL("jdbc:mysql:", '?',
+            new String[]{"connectTimeout"}, 1000, 0,
+            new String[]{"socketTimeout"}, 1000, true,
+            new int[]{1040, 1203}, new int[]{1053}),
+        /** oracle: both properties take milliseconds; ReadTimeout is a socket read timeout that outlives the login. */
+        ORACLE("jdbc:oracle:", '?',
+            new String[]{"oracle.net.CONNECT_TIMEOUT"}, 1000, 0,
+            // the read bound goes by two names the driver reads: the property set here and the
+            // property of oracle net it stands for, inside a tns descriptor by the last segment of
+            // either. A bound under one of them is a bound of the administrator, so ours is not set
+            // on top of it - and neither of theirs is lifted with ours once the login is through.
+            // Only the first of the two is a name the driver also reads out of the system
+            // properties (SYSTEM_PROPERTY_NAMES below): oracle.net.READ_TIMEOUT reaches the socket
+            // from the connection properties alone, so a -D of it bounds nothing and must not be
+            // taken for a bound of theirs.
+            // RECV_TIMEOUT is not one of them: it is a parameter of sqlnet.ora and of the listener,
+            // and the name does not appear in ojdbc8 at all, so a descriptor carrying one would
+            // have taken our bound off a connection that never had one of its own.
+            new String[]{"oracle.jdbc.ReadTimeout", "oracle.net.READ_TIMEOUT"}, 1000, true,
+            // ORA-01033 and ORA-01034: the instance is starting up or not there yet; ORA-01089:
+            // it is shutting down. ORA-12514 is left out of these on purpose - a listener that
+            // does not know the service is also what a service name of a typo looks like, forever
+            new int[]{20, 12516, 12518, 12519, 12520}, new int[]{1033, 1034, 1089}),
+        /**
+         * ms sql server: loginTimeout takes seconds, socketTimeout milliseconds; the latter is a
+         * socket read timeout that outlives the login. loginTimeout is the one property of the
+         * four with a range of its own - SQLServerDriverIntProperty.LOGIN_TIMEOUT is validated
+         * against [0, 65535], and a value beyond it fails every connect the driver is asked for.
+         */
+        MICROSOFT("jdbc:sqlserver:", ';',
+            new String[]{"loginTimeout"}, 1, 65535,
+            new String[]{"socketTimeout"}, 1000, true,
+            // 921 and 922: the database has not been recovered yet, or is being recovered; 927: it
+            // is in the middle of a restore; 40613: azure sql reporting it not available for now
+            new int[]{17809, 10928, 10929}, new int[]{921, 922, 927, 40613});
+
+        final String urlPrefix;
+        /** the character that separates the parameters of this dialect from the url in front of them */
+        final char parameterSeparator;
+        /** the properties bounding the connect: the socket connect, and whatever the driver wraps it in */
+        final String[] connectProperties;
+        final int connectUnitsPerSecond;
+        /** the largest value the driver accepts for a connect property, 0 for a driver that takes any */
+        final long maxConnectSeconds;
+        /** the read bound of the login: the first name is the one set here, the rest are the names it also goes by */
+        final String[] readProperties;
+        final int readUnitsPerSecond;
+        /** whether the read bound of the login stays in force for every statement issued afterwards */
+        final boolean readBoundOutlivesLogin;
+        /** the vendor codes of this dialect for "no further connection is accepted" */
+        final int[] connectionLimitCodes;
+        /** the vendor codes of this dialect for "not accepting connections yet": a database on its way up */
+        final int[] notAcceptingYetCodes;
+
+        ConnectDialect(String urlPrefix, char parameterSeparator,
+                       String[] connectProperties, int connectUnitsPerSecond, long maxConnectSeconds,
+                       String[] readProperties, int readUnitsPerSecond, boolean readBoundOutlivesLogin,
+                       int[] connectionLimitCodes, int[] notAcceptingYetCodes) {
+            this.urlPrefix = urlPrefix;
+            this.parameterSeparator = parameterSeparator;
+            this.connectProperties = connectProperties;
+            this.connectUnitsPerSecond = connectUnitsPerSecond;
+            this.maxConnectSeconds = maxConnectSeconds;
+            this.readProperties = readProperties;
+            this.readUnitsPerSecond = readUnitsPerSecond;
+            this.readBoundOutlivesLogin = readBoundOutlivesLogin;
+            this.connectionLimitCodes = connectionLimitCodes;
+            this.notAcceptingYetCodes = notAcceptingYetCodes;
+        }
+
+        /** The dialect of a connection string, or null for a driver whose property names are not known here. */
+        static ConnectDialect of(String connectionString) {
+            final String url = connectionString.toLowerCase(Locale.ROOT);
+            for (final ConnectDialect dialect : values()) {
+                if (url.startsWith(dialect.urlPrefix)) {
+                    return dialect;
+                }
+            }
+            return null;
+        }
+
+        /**
+         * Fills in the properties bounding one connect attempt, leaving out what the administrator
+         * bounded themselves - an explicit setting of theirs keeps precedence, on the SQL Server,
+         * mysql and oracle drivers because a supplied property outranks the url, and on postgresql
+         * because the url outranks the property. A driver with a range of its own for its connect
+         * property is not handed a value beyond it: a bound it rejects is no bound at all, it is a
+         * connect that never happens.
+         * Returns whether a read bound outliving the login was set and has to be lifted once the
+         * connection is established.
+         */
+        boolean bound(String connectionString, Properties properties, long timeoutSeconds) {
+            final long connectSeconds = maxConnectSeconds > 0
+                ? Math.min(timeoutSeconds, maxConnectSeconds) : timeoutSeconds;
+            // The connect side is one budget rather than a set of independent knobs, so a bound of
+            // the administrator under any of its names leaves all of them alone. On postgresql
+            // connectTimeout bounds the socket connect and loginTimeout the login behind it:
+            // filling in the one they left out caps the one they set, and a "?connectTimeout=300"
+            // answered with a loginTimeout of ours is a login pgjdbc gives up on at 30 s - Driver
+            // .connect branches into its own thread as soon as loginTimeout is anything but 0.
+            if (!declared(connectionString, connectProperties)) {
+                for (final String property : connectProperties) {
+                    properties.setProperty(property, Long.toString(connectSeconds * connectUnitsPerSecond));
+                }
+            }
+            reportBoundTurnedOffInUrl(connectionString);
+            if (!declared(connectionString, readProperties)) {
+                properties.setProperty(readProperties[0], Long.toString(timeoutSeconds * readUnitsPerSecond));
+                return readBoundOutlivesLogin;
+            }
+            return false;
+        }
+
+        /**
+         * Reports a url that turns a bound off where nothing this class supplies can put one back.
+         * A parameter of a postgresql url outranks the property this class hands the driver, so a
+         * "socketTimeout=0" there is not a default to be replaced - it is the administrator asking
+         * for an unbounded read, and a borrow that meets a database accepting the connection and
+         * answering nothing is then parked with no deadline able to reach it.
+         */
+        private void reportBoundTurnedOffInUrl(String connectionString) {
+            if (!urlOutranksProperties()) {
+                return;
+            }
+            // Every one of them, and keyed by the property rather than by the url alone: a url
+            // turns off the read bound and the login bound both ("?socketTimeout=0&loginTimeout=0",
+            // where the second is the per-host budget of a failover url), and safeUrl() keeps none
+            // of the timeout parameters - so a single key would report the first offender and
+            // leave the administrator to find the rest of them on their own.
+            for (final String[] properties : new String[][]{readProperties, connectProperties}) {
+                for (final String property : properties) {
+                    final String value = parameterValue(connectionString, property);
+                    if (value != null && !isBound(value)) {
+                        warnOnce(safeUrl(connectionString) + "|unbounded|" + property,
+                            "%s sets \"%s=%s\": a parameter of a postgresql url outranks the property this backend"
+                                + " supplies, so that phase of a connect carries no bound. An operation reaching a"
+                                + " database that accepts the connection and does not answer stays parked",
+                            safeUrl(connectionString), property, value);
+                    }
+                }
+            }
+        }
+
+        /** Whether a vendor code of this dialect is one that waiting for the database can clear. */
+        boolean isWorthRetrying(int errorCode) {
+            return contains(connectionLimitCodes, errorCode) || contains(notAcceptingYetCodes, errorCode);
+        }
+
+        private static boolean contains(int[] codes, int code) {
+            for (final int candidate : codes) {
+                if (candidate == code) {
+                    return true;
+                }
+            }
+            return false;
+        }
+
+        // Whether the administrator bounded one of these properties themselves. The dialects
+        // separate their parameters differently - "?a=1&b=2" (postgresql, mysql), ";a=1;b=2" (sql
+        // server), "(A=1)" inside the descriptor of an oracle tns url, where the property also goes
+        // by the last segment of its name alone - so a parameter is recognized by the delimiter in
+        // front of it and the "=" behind it rather than by parsing the url syntax of every driver.
+        // The connection string is not the only channel of theirs: the oracle driver reads some of
+        // its properties out of the system properties as well, which is how a whole jvm is bounded
+        // with -Doracle.jdbc.ReadTimeout, and a property supplied to a driver outranks the system
+        // property without a word - and would then be lifted after the login as if it were ours,
+        // leaving a connection with no read bound where the administrator had set one.
+        private boolean declared(String connectionString, String... properties) {
+            for (final String property : properties) {
+                if (declaredInUrl(connectionString, property) || setAsSystemProperty(property)) {
+                    return true;
+                }
+            }
+            return false;
+        }
+
+        /** Whether the connection string bounds this property, under its own name or the last segment of it. */
+        private boolean declaredInUrl(String connectionString, String property) {
+            if (containsParameter(connectionString, property)) {
+                return true;
+            }
+            final int dot = property.lastIndexOf('.');
+            return dot >= 0 && containsParameter(connectionString, property.substring(dot + 1));
+        }
+
+        // Which names a driver reads out of the system properties, listed rather than told from
+        // the shape of the name: ojdbc8 resolves oracle.jdbc.ReadTimeout and
+        // oracle.net.CONNECT_TIMEOUT in three tiers (the properties it was supplied, then
+        // System.getProperty, then the properties of the data source), while
+        // oracle.net.READ_TIMEOUT - a dotted name of the same driver - is read out of the
+        // connection properties alone: the six classes carrying the literal hand it to
+        // Properties.get, and none of them to System.getProperty. Taking a -D of it for a bound of
+        // the administrator would leave the login with no read bound at all - theirs not read by
+        // the driver and ours not set, because we believed theirs was in force.
+        private static final Set<String> SYSTEM_PROPERTY_NAMES = Collections.unmodifiableSet(new HashSet<>(
+            Arrays.asList("oracle.jdbc.ReadTimeout", "oracle.net.CONNECT_TIMEOUT")));
+
+        private static boolean setAsSystemProperty(String property) {
+            return SYSTEM_PROPERTY_NAMES.contains(property) && isBound(System.getProperty(property));
+        }
+
+        // pgjdbc parses the url over the properties it was handed - Driver.connect copies them
+        // into a flat map and parseURL then writes the parameters of the url on top - so a value
+        // standing in a postgresql url is the value the driver uses, and the one supplied here
+        // never reaches the socket. A zero there is not a default of the driver to be replaced: it
+        // cannot be replaced, and setting ours on top of it would leave this class lifting a read
+        // bound the login never had. The other three let a supplied property win, so a zero of
+        // theirs is ours to override.
+        private boolean urlOutranksProperties() {
+            return this == POSTGRES;
+        }
+
+        /** Whether this property is bounded by the connection string, as the driver of this dialect reads it. */
+        private boolean containsParameter(String connectionString, String property) {
+            final String value = parameterValue(connectionString, property);
+            return value != null && (urlOutranksProperties() || isBound(value));
+        }
+
+        // Matched the way the driver of this dialect matches it: pgjdbc and Connector/J look their
+        // properties up by their exact name - PropertyKey.fromValue answers null for a name of
+        // another case and the parameter is then a parameter of nobody, so "?SocketTimeout=" must
+        // not be taken for a bound of the administrator - while the SQL Server driver
+        // (getNormalizedPropertyName) and the keywords of an oracle descriptor match either way.
+        private String parameterValue(String connectionString, String property) {
+            final boolean exact = this == POSTGRES || this == MYSQL;
+            final String url = exact ? connectionString : connectionString.toLowerCase(Locale.ROOT);
+            final String name = exact ? property : property.toLowerCase(Locale.ROOT);
+            String value = null;
+            for (int i = url.indexOf(name); i >= 0; i = url.indexOf(name, i + name.length())) {
+                final int end = i + name.length();
+                if (i > 0 && "?&;(,".indexOf(url.charAt(i - 1)) >= 0 && end < url.length() && url.charAt(end) == '=') {
+                    // the last of them: a driver parsing a url into a map lets the last assignment stand
+                    value = valueOf(url, end + 1);
+                }
+            }
+            return value;
+        }
+
+        /** The value of the parameter that starts here: up to the delimiter in front of the next one. */
+        private static String valueOf(String url, int from) {
+            int end = from;
+            while (end < url.length() && "&;),?".indexOf(url.charAt(end)) < 0) {
+                end++;
+            }
+            return url.substring(from, end);
+        }
+
+        /**
+         * Whether a value of the administrator bounds anything. Every one of these drivers reads 0
+         * as "wait as long as it takes", so a property set to it is not a bound of theirs to stay
+         * out of the way of - it is the default this class exists to replace, and one of ours goes
+         * on top of it wherever a supplied property outranks the url. Where it does not, on
+         * postgresql, the zero stands and is reported instead of being written over. A value that
+         * is no number is left to the driver it belongs to.
+         */
+        private static boolean isBound(String value) {
+            if (value == null || value.trim().isEmpty()) {
+                return false;
+            }
+            try {
+                return Double.parseDouble(value.trim()) != 0; // pgjdbc takes a float for its loginTimeout
+            } catch (NumberFormatException notANumber) {
+                return true;
+            }
+        }
     }
 
     final String connectionString;
+    /**
+     * Whether this connection may go back into the pool once it is closed. A connection carrying a
+     * read bound that could not be lifted serves the borrower waiting for it and is closed
+     * afterwards: left in the pool it would fail every statement slower than that bound - an
+     * import batch among them - for every borrow the pool hands it to.
+     */
+    private final boolean poolable;
+
+    /**
+     * When this connection last answered the database, as a {@link System#nanoTime()} reading:
+     * established - the login and the two round trips that set it up have just answered - or
+     * validated. It is never stamped on the way back into the pool, although that is where a
+     * connection has most recently been used: {@link #close()} ends the transaction, and pgjdbc
+     * short-circuits both {@code rollback()} and {@code commit()} when the transaction state is
+     * IDLE, so on a borrow that issued no statement - {@code JDBCStorage.open()}, a configuration
+     * change that leaves the base DNs alone, an import of nothing - not a byte reaches the server
+     * and the stamp would prove nothing, while marking a connection the database may have dropped
+     * as the freshest one in the pool. Stamping proof rather than use makes the window mean
+     * "validated at most once per window", which is a claim this class can always back.
+     * <p>
+     * It stands for the moment the connection was <em>asked</em>, not the moment its answer was
+     * filed: {@link #distrustPool} is compared against it as an ordering of two moments, and a
+     * proof that took a second to arrive would otherwise outlive a drop reported while it was
+     * still in flight. Reading it early only ever ages the proof, which costs a validation and
+     * never skips one.
+     */
+    private volatile long lastKnownAliveNanos;
+
     public CachedConnection(String connectionString, Connection parent) {
+        this(connectionString, parent, true);
+    }
+
+    CachedConnection(String connectionString, Connection parent, boolean poolable) {
         this.connectionString = connectionString;
         this.parent = parent;
+        this.poolable = poolable;
+        this.lastKnownAliveNanos = System.nanoTime();
     }
 
+    /**
+     * Borrows a connection: a usable one out of the pool, or a newly established one. Bounded in
+     * both phases - every operation of this backend, the open of a backend and the import
+     * included, comes through here, and an unbounded borrow turns a database that listens but does
+     * not answer into a hang rather than into an error the caller can report.
+     */
     static Connection getConnection(String connectionString) throws Exception {
-        return getConnection(connectionString, 0);
+        return getConnection(connectionString, true);
     }
 
-    static Connection getConnection(String connectionString, final int waitTime) throws Exception {
-        CachedConnection con = cached.get(connectionString).poll(waitTime, TimeUnit.MILLISECONDS);
-
-        while (con != null) {
-            if (!con.isValid(0)) {
-                try {
-                    con.parent.close();
-                } catch (SQLException e) {
-                    con = null;
+    /**
+     * Borrows a connection, either trusting the alive window of {@value #ALIVE_BYPASS_PROPERTY} or
+     * validating whatever comes out of the pool.
+     *
+     * @param trusted false for a borrow nothing compensates a dropped connection on. What the
+     * window trades away is the connection that breaks inside it, and {@code JDBCStorage} takes
+     * that off the caller where it can - a write is replayed, a read tells the pool - but the
+     * borrows that open a backend, remove its files or start an import have neither: they issue
+     * their statements far from the borrow, and the one that opens a backend issues none at all,
+     * so a dropped connection would surface out of the {@code rollback()} of its release. Each of
+     * them is one borrow of a cold path, where the round trip the window saves is worth nothing.
+     */
+    static Connection getConnection(String connectionString, boolean trusted) throws Exception {
+        final ConnectDialect dialect = ConnectDialect.of(connectionString);
+        reportUnknownDialect(connectionString, dialect);
+        final long connectTimeoutSeconds = Math.min(
+            getNonNegativeProperty(CONNECT_TIMEOUT_PROPERTY, DEFAULT_CONNECT_TIMEOUT_SECONDS, "s"),
+            Integer.MAX_VALUE / 1000);
+        final long poolTimeoutSeconds = getNonNegativeProperty(POOL_TIMEOUT_PROPERTY, DEFAULT_POOL_TIMEOUT_SECONDS, "s");
+        final long startedAt = System.currentTimeMillis();
+        final long deadline = (poolTimeoutSeconds == 0 || poolTimeoutSeconds >= Long.MAX_VALUE / 1000)
+            ? Long.MAX_VALUE : startedAt + poolTimeoutSeconds * 1000;
+        long waitMs = 0;
+        long backoffMs = 0;
+        int attempts = 0;
+        while (true) {
+            final CachedConnection pooled = poll(connectionString, waitMs, deadline, trusted);
+            if (pooled != null) {
+                return pooled;
+            }
+            attempts++;
+            try {
+                return connect(connectionString, dialect, attemptSeconds(connectTimeoutSeconds, deadline));
+            } catch (SQLException e) {
+                // A database that takes no connection for the moment is the failure worth waiting
+                // out: it is at its connection limit, and one of ours is going to come back to the
+                // pool - or it is on its way up, and the state clears itself in seconds. Everything
+                // else - a password that is not accepted, a database that is down, a driver that is
+                // not on the classpath - is reported to the caller instead of being retried behind
+                // its back.
+                if (!isWorthRetrying(e, dialect)) {
+                    throw reported(e, connectionString);
                 }
-                con = cached.get(connectionString).poll();
-            } else {
-                return con;
+                final long remaining = deadline - System.currentTimeMillis();
+                if (remaining <= 0) {
+                    // 08001, the state of a connect that did not happen, rather than none at all:
+                    // this is the failure of a borrow, and a caller reading the state of what it
+                    // caught would otherwise see null where the driver's own exception carried one
+                    final SQLTimeoutException timeout = new SQLTimeoutException("no connection to "
+                        + safeUrl(connectionString) + " could be borrowed within " + poolTimeoutSeconds + "s ("
+                        + attempts + " attempts): the database took no connection for the moment and none was"
+                        + " returned to the pool, last error: " + redact(e.getMessage(), connectionString),
+                        CONNECT_FAILED_SQL_STATE);
+                    timeout.initCause(reported(e, connectionString));
+                    throw timeout;
+                }
+                backoffMs = Math.min(backoffMs == 0 ? 1 : backoffMs * 2, MAX_BACKOFF_MS);
+                waitMs = Math.min(backoffMs, remaining);
+                warnStall(connectionString, attempts, startedAt, e);
+            } catch (RuntimeException e) {
+                // a driver reporting a connect it will not make as an unchecked failure carries the
+                // connection string of the backend in its message as readily as a SQLException does
+                throw reportedUnchecked(e, connectionString);
             }
         }
-        Connection conNew = null;
+    }
+
+    /**
+     * Reports a connection string this class knows no bound for. The properties bounding a connect
+     * are the ones of a driver, so a driver outside the four leaves every attempt unbounded - and
+     * the deadline of the borrow cannot reach into a connect that is already under way, since the
+     * driver is the only thing holding the socket.
+     */
+    private static void reportUnknownDialect(String connectionString, ConnectDialect dialect) {
+        if (dialect != null) {
+            return;
+        }
+        final StringBuilder known = new StringBuilder();
+        for (final ConnectDialect candidate : ConnectDialect.values()) {
+            known.append(known.length() > 0 ? ", " : "").append(candidate.urlPrefix);
+        }
+        warnOnce(safeUrl(connectionString) + "|unknown-dialect",
+            "%s names a driver whose timeout properties are not known to this backend (%s are): a connect to a"
+                + " database that accepts it and does not answer is left without a bound, and the %s property"
+                + " cannot end it",
+            safeUrl(connectionString), known, POOL_TIMEOUT_PROPERTY);
+    }
+
+    /**
+     * The bound of one connect attempt. The deadline of the borrow bounds it as well - the
+     * {@value #POOL_TIMEOUT_PROPERTY} property stands for the whole borrow, and an attempt of its
+     * own left to run out would overrun it by a full connect timeout. That holds for an attempt
+     * the {@value #CONNECT_TIMEOUT_PROPERTY} property gives no bound of its own, too: turning the
+     * per-attempt bound off must not turn the bound of the borrow off with it. Never 0 for an
+     * attempt that is bounded at all: 0 is the value that stands for no bound. And never past what
+     * an int of milliseconds takes - the pool timeout has no upper bound of its own, while the SQL
+     * Server driver rejects a socketTimeout beyond Integer.MAX_VALUE outright, failing every
+     * connect of that backend with the name of a property nobody typed.
+     */
+    static long attemptSeconds(long connectTimeoutSeconds, long deadline) {
+        if (deadline == Long.MAX_VALUE) {
+            // 0 stands for an attempt with no bound of its own and stays 0; anything else is
+            // clamped here as well, so that the range holds whichever branch answers
+            return connectTimeoutSeconds == 0 ? 0 : Math.min(connectTimeoutSeconds, Integer.MAX_VALUE / 1000);
+        }
+        final long remainingSeconds = (deadline - System.currentTimeMillis() + 999) / 1000;
+        final long bound = connectTimeoutSeconds == 0
+            ? remainingSeconds : Math.min(connectTimeoutSeconds, remainingSeconds);
+        return Math.max(1, Math.min(bound, Integer.MAX_VALUE / 1000));
+    }
+
+    /**
+     * Takes a usable connection out of the pool, waiting up to waitMs for one to be returned to it.
+     * The validation of a connection costs a round trip, and the pool has no upper bound on the
+     * number of them it holds, so draining a pool the database no longer answers is given the
+     * deadline of the borrow as well: past it, establishing a connection is the faster answer.
+     * The connection in hand is always looked at first - trusted or validated, see
+     * {@link #isKnownAlive} - whatever the deadline says: a database at its connection limit has
+     * no other source of connections than the ones coming back, and one returned to the pool a
+     * moment before the deadline is the very connection this borrow waited for. Only a connection
+     * the database no longer answers is closed here.
+     */
+    private static CachedConnection poll(String connectionString, long waitMs, long deadline, boolean trusted)
+            throws InterruptedException {
+        CachedConnection con = cached.get(connectionString).pollFirst(waitMs, TimeUnit.MILLISECONDS);
+        while (con != null) {
+            if (isUsable(con, trusted)) {
+                return con;
+            }
+            closeQuietly(con.parent);
+            if (System.currentTimeMillis() >= deadline) {
+                return null;
+            }
+            con = cached.get(connectionString).pollFirst();
+        }
+        return null;
+    }
+
+    private static boolean isUsable(CachedConnection con, boolean trusted) {
+        if (trusted && isKnownAlive(con)) {
+            return true;
+        }
+        // The validation needs a bound of its own: isValid(0) means "no timeout" in the JDBC
+        // contract, and a connection whose socket is half-open answers it no sooner than it
+        // answers anything else. isValid(n) is not that bound on every driver either - the SQL
+        // Server driver turns it into a query timeout (setQueryTimeout, then "SELECT 1"), which
+        // needs an answer from the server to fire at all - so the socket is bounded here, for the
+        // validation only.
+        final int restore = boundValidation(con.parent);
+        if (restore == VALIDATION_BOUND_FAILED) {
+            // the bound of the validation is not in force, and the driver may well have applied it
+            // before failing: validating here would be the unbounded isValid() this exists to
+            // avoid, and pooling it would hand out a connection carrying a bound of ours
+            return false;
+        }
+        // Read before the round trip rather than after it: this stamp is what distrustPool() is
+        // compared against, as an ordering of two moments. A validation is allowed
+        // VALIDATION_TIMEOUT_SECONDS, so a stamp filed once the answer is in can be younger than a
+        // drop another operation reported while it was still in flight - and the connection would
+        // then be trusted for the rest of the window by the very check that exists to stop it.
+        final long provenAt = System.nanoTime();
+        boolean usable;
         try {
-            conNew = DriverManager.getConnection(connectionString);
+            usable = con.isValid(VALIDATION_TIMEOUT_SECONDS);
+        } catch (SQLException | RuntimeException e) { // a driver reporting the validation as an error: discard it
+            // an unchecked failure out of a driver would unwind through poll(), which stands
+            // outside every try of the borrow, and leave this connection dequeued and unclosed
+            usable = false;
+        }
+        if (!usable) {
+            // On its way out, and the driver knows it: Connector/J answers a failed validation by
+            // aborting the connection and the SQL Server driver by terminating it, so putting the
+            // previous bound back would fail as well - and warn about a bound of a connection that
+            // is about to be closed, over a reaped idle connection that is nobody's problem.
+            return false;
+        }
+        if (restore >= 0 && !setNetworkTimeout(con.parent, restore,
+                "the connection is closed rather than pooled")) {
+            return false; // it would carry the bound of the validation into every statement
+        }
+        con.lastKnownAliveNanos = provenAt;
+        return true;
+    }
+
+    /** A connection left alone by {@link #boundValidation}: no bound of ours to put back afterwards. */
+    private static final int VALIDATION_BOUND_LEFT_ALONE = -1;
+    /** A connection {@link #boundValidation} could not bound, which may still carry the bound it failed to report. */
+    private static final int VALIDATION_BOUND_FAILED = -2;
+
+    /**
+     * Whether a connection can be handed out on the strength of the last answer it gave, without a
+     * round trip to ask for another. Three things have to hold: the window is on, the answer is
+     * younger than it, and nothing has reported since that the database dropped a connection of
+     * this pool.
+     * <p>
+     * What the window trades away is the connection that breaks inside it: it is handed out, and
+     * the failure surfaces on the statement of the caller rather than on the borrow. That is where
+     * a connection breaking mid-operation surfaces anyway - but not every caller of this backend
+     * reports such a failure to the client, so the trade is not the caller's alone to bear.
+     * {@code JDBCStorage} answers it on both sides: a write is replayed on a connection the next
+     * attempt borrows of its own, and a read as much as a write marks the pool distrusted, which
+     * closes the window for the rest of the generation the dropped connection belonged to.
+     */
+    private static boolean isKnownAlive(CachedConnection con) {
+        final long window = aliveBypassNanos;
+        if (window <= 0) {
+            return false;
+        }
+        final long provenAt = con.lastKnownAliveNanos;
+        if (System.nanoTime() - provenAt >= window) { // the overflow safe form of the comparison
+            return false;
+        }
+        final Long distrusted = poolDistrustedAt.get(con.connectionString);
+        if (distrusted != null && provenAt - distrusted <= 0) { // the overflow safe form of the comparison
+            return false;
+        }
+        // What the validation this replaces also answered: the removalListener above closes every
+        // connection it finds in the deque when the pool expires, and it iterates a weakly
+        // consistent view, so a connection taken out by a borrow running at the same time can be
+        // closed under it. Answered by the driver out of a flag of its own, not by a round trip.
+        return !isClosed(con.parent);
+    }
+
+    /** Whether the driver reports the connection as closed; one that cannot say is not one to trust. */
+    private static boolean isClosed(Connection con) {
+        try {
+            return con.isClosed();
+        } catch (SQLException e) {
+            return true;
+        }
+    }
+
+    /**
+     * Reports that the database dropped a connection of this pool, so that no connection proven
+     * alive before now is handed out unvalidated again. It is called by the operation that saw the
+     * failure: this class only ever learns of one from the statement it broke, since a borrow
+     * inside the window asks the database nothing.
+     */
+    static void distrustPool(String connectionString) {
+        // merge(later of the two) rather than computeIfAbsent().set(): two operations reporting a
+        // drop at once would otherwise move the distrust point backwards - the later reading is
+        // written first and the earlier one overwrites it - and the AtomicLong of computeIfAbsent
+        // is published holding its initial 0 before set() runs, which a borrow racing it reads as
+        // "never". Not Math.max: nanoTime() has no defined origin, so the readings are compared by
+        // their difference, the way every other comparison of one in this class is.
+        poolDistrustedAt.merge(connectionString, System.nanoTime(),
+            (reported, now) -> now - reported > 0 ? now : reported);
+    }
+
+    /**
+     * Bounds the socket of a pooled connection for the length of its validation, returning the
+     * network timeout to put back afterwards - or {@link #VALIDATION_BOUND_LEFT_ALONE} for a
+     * connection left alone, either because the driver does not take a network timeout or because
+     * it is bounded at least as tightly already, by a read timeout of the connection string that
+     * is not ours to widen.
+     * A driver that takes the call and then fails inside it is told apart from both: it is free to
+     * have applied the bound before failing, and a connection put back into the pool carrying five
+     * seconds of ours fails every statement slower than that for the rest of its life.
+     */
+    private static int boundValidation(Connection con) {
+        final int bound = VALIDATION_TIMEOUT_SECONDS * 1000;
+        final int previous;
+        try {
+            previous = con.getNetworkTimeout();
+        } catch (SQLException | RuntimeException e) { // a driver that does not take one: nothing was changed
+            return VALIDATION_BOUND_LEFT_ALONE;
+        }
+        if (previous > 0 && previous <= bound) {
+            return VALIDATION_BOUND_LEFT_ALONE;
+        }
+        try {
+            con.setNetworkTimeout(DIRECT_EXECUTOR, bound);
+        } catch (SQLException | RuntimeException e) {
+            return VALIDATION_BOUND_FAILED;
+        }
+        // A driver answering a negative timeout is outside the contract of getNetworkTimeout(),
+        // where 0 stands for no limit and nothing below it stands for anything. Handed back as it
+        // is, it would be one of the two sentinels above: the bound just set would be read as a
+        // bound that was never set, and the connection would go into the pool carrying five
+        // seconds of ours into every statement of whoever borrows it next.
+        return previous < 0 ? 0 : previous;
+    }
+
+    static CachedConnection connect(String connectionString, ConnectDialect dialect, long connectTimeoutSeconds)
+            throws SQLException {
+        // A driver is free to write into the map it is handed, so it gets one of its own.
+        final Properties properties = new Properties();
+        final boolean readBoundSet = dialect != null && connectTimeoutSeconds > 0
+            && dialect.bound(connectionString, properties, connectTimeoutSeconds);
+        // Read before the connect rather than after it, for the reason isUsable() reads it before
+        // the validation: the login answered somewhere inside this attempt, and a stamp taken once
+        // it returned could outlive a drop reported while it was still going on.
+        final long provenAt = System.nanoTime();
+        final Connection conNew = DriverManager.getConnection(connectionString, properties);
+        boolean poolable = true;
+        try {
+            // still under the read bound: both of these are round trips of their own
             conNew.setAutoCommit(false);
             conNew.setTransactionIsolation(TRANSACTION_READ_COMMITTED);
-            return new CachedConnection(connectionString, conNew);
-        } catch (SQLException e) { // max_connection server error: try recursion for reuse connection
-            if (conNew != null) { // the connection was established but not set up: nothing else would close it
-                try {
-                    conNew.close();
-                } catch (SQLException e2) {}
+            if (readBoundSet) {
+                // a driver that will not take the bound back has warned about it already: the
+                // connection serves the borrower that is waiting for it and is closed rather than
+                // pooled, so the bound of the login does not outlive it in the pool
+                poolable = relaxReadBound(conNew, connectTimeoutSeconds);
             }
-            return getConnection(connectionString, (waitTime == 0) ? 1 : waitTime * 2);
+        } catch (SQLException | RuntimeException e) { // nothing holds this connection yet: it would leak
+            closeQuietly(conNew);
+            throw e;
+        }
+        final CachedConnection established = new CachedConnection(connectionString, conNew, poolable);
+        established.lastKnownAliveNanos = provenAt;
+        return established;
+    }
+
+    // The second bound of the login is a socket read timeout on mysql, oracle and sql server, in
+    // force for the whole life of the connection: left in place it would break every statement
+    // slower than it - an import batch, the statistics of a freshly loaded table - so it is lifted
+    // as soon as the login is through, restoring the behaviour of a connection this class
+    // established before. A read bound the connection string sets itself is never touched here:
+    // it is not set at all, so nothing of the administrator's is lifted along with it. Returns
+    // whether the bound is gone - a connection still carrying it must not be pooled.
+    // Named by the bound the login was given rather than by the property it came from: with
+    // CONNECT_TIMEOUT_PROPERTY at 0 the attempt takes its bound from what is left of the deadline
+    // of the borrow, so naming that property would point at the one setting that is not in force.
+    private static boolean relaxReadBound(Connection con, long boundSeconds) {
+        return setNetworkTimeout(con, 0, "statements taking longer than the " + boundSeconds
+            + "s the login of this connection was bounded by fail on it, and it is closed rather than pooled");
+    }
+
+    /**
+     * Puts a network timeout on a connection, reporting a driver that will not take one. The
+     * consequence is the caller's to name: the same failure ends a freshly established connection
+     * carrying the read bound of its login and a pooled one whose bound could not be put back.
+     */
+    private static boolean setNetworkTimeout(Connection con, int millis, String consequence) {
+        try {
+            con.setNetworkTimeout(DIRECT_EXECUTOR, millis);
+            return true;
+        } catch (SQLException | RuntimeException e) {
+            // Throttled rather than reported once for the life of the JVM: every connection this
+            // happens to carries a read bound it was never meant to keep, and a statement dying of
+            // it hours later needs a warning of its own to be traced back to here.
+            final long now = System.currentTimeMillis();
+            final long last = lastReadBoundWarning.get();
+            if (now - last >= STALL_WARNING_INTERVAL_MS && lastReadBoundWarning.compareAndSet(last, now)) {
+                logger.warn(LocalizableMessage.raw(
+                    "The read bound of a JDBC connection could not be set to %d ms (%s): %s",
+                    millis, e.getMessage(), consequence));
+            }
+            return false;
+        }
+    }
+
+    /**
+     * Whether the database took no connection for the moment, rather than refusing one for good:
+     * it is at its connection limit - one of our own connections is on its way back to the pool -
+     * or it is not accepting connections yet, the state a database on its way up reports while it
+     * recovers - the one JDBCStorage.open() has no second attempt of its own for, so a backend
+     * that meets it stays locked down until the server is restarted. Both clear themselves in
+     * seconds; every other failure is the caller's to see.
+     */
+    static boolean isWorthRetrying(SQLException e, ConnectDialect dialect) {
+        // a failure of the driver is often wrapped, and a SQLException carries two chains of its
+        // own: the causes behind it and the further exceptions of getNextException()
+        final Deque<Throwable> pending = new ArrayDeque<>();
+        final Set<Throwable> visited = Collections.newSetFromMap(new IdentityHashMap<Throwable, Boolean>());
+        enqueue(pending, visited, e);
+        for (int links = 0; !pending.isEmpty() && links < MAX_CHAIN_LENGTH; links++) {
+            final Throwable t = pending.poll();
+            if (t instanceof SQLException) {
+                final SQLException sql = (SQLException) t;
+                final String sqlState = sql.getSQLState();
+                if (CONNECTION_LIMIT_SQL_STATE.equals(sqlState) || NOT_ACCEPTING_YET_SQL_STATE.equals(sqlState)
+                    || (dialect != null && dialect.isWorthRetrying(sql.getErrorCode()))) {
+                    return true;
+                }
+                enqueue(pending, visited, sql.getNextException());
+            }
+            enqueue(pending, visited, t.getCause());
+        }
+        return false;
+    }
+
+    // A stall has to reach the server log: without it a database accepting no further connection
+    // is indistinguishable from a hang. Throttled, since every operation of the backend borrows
+    // through here and would otherwise log a copy of its own.
+    private static void warnStall(String connectionString, int attempts, long startedAt, SQLException cause) {
+        final long now = System.currentTimeMillis();
+        if (now - startedAt < STALL_WARNING_AFTER_MS) {
+            return;
+        }
+        final AtomicLong lastOfThisUrl =
+            lastStallWarning.computeIfAbsent(safeUrl(connectionString), url -> new AtomicLong());
+        final long last = lastOfThisUrl.get();
+        if (now - last >= STALL_WARNING_INTERVAL_MS && lastOfThisUrl.compareAndSet(last, now)) {
+            logger.warn(LocalizableMessage.raw("%s", stallMessage(connectionString, attempts, now - startedAt, cause)));
+        }
+    }
+
+    /**
+     * The stall as it reaches the log. Built apart from the logging of it so that the rule it has
+     * to keep - neither the connection string nor the message of the driver reaches a log as it
+     * stands - is a rule a test can hold it to.
+     */
+    static String stallMessage(String connectionString, int attempts, long waitedMs, SQLException cause) {
+        return String.format("%s takes no further connection: waiting %d ms for a pooled one so far (%d attempts),"
+            + " last error: %s", safeUrl(connectionString), waitedMs, attempts,
+            redact(cause.getMessage(), connectionString));
+    }
+
+    /**
+     * The failure of a connect as it may leave this class: the exception itself where nothing of it
+     * names the credentials of the backend, and a redacted rebuild of its whole chain where
+     * something does. Rebuilt rather than wrapped: a wrapper keeps its cause, and everything that
+     * prints a failure prints the causes along with it - a debug build of
+     * stackTraceToSingleLineString walks them, the config manager traces them, and
+     * RootContainer.open() makes the message of the cause the message of what it throws - so a
+     * link left as it stands would carry the password past the wrapper. The SQLState and the
+     * vendor code of every link survive it: they are what tells a caller what happened.
+     */
+    static SQLException reported(SQLException e, String connectionString) {
+        return holdsCredentials(e, connectionString)
+            ? redactedCopy(e, connectionString, new int[] { MAX_CHAIN_LENGTH })
+            : e;
+    }
+
+    /** The same of an unchecked failure: a driver is free to report a connect it will not make as one. */
+    static Exception reportedUnchecked(RuntimeException e, String connectionString) {
+        if (!holdsCredentials(e, connectionString)) {
+            return e;
+        }
+        final SQLException redacted = new SQLNonTransientConnectionException(e.getClass().getName()
+            + (e.getMessage() == null ? "" : ": " + redact(e.getMessage(), connectionString)),
+            CONNECT_FAILED_SQL_STATE);
+        redacted.setStackTrace(e.getStackTrace());
+        return redacted;
+    }
+
+    /**
+     * Whether anything in the chain of a failure names what a connection string keeps out of the
+     * log. A chain longer than this walk is given answers "yes": what is reported unredacted is
+     * what this class has looked at whole, and a link it never reached is not that. The cost of
+     * being wrong that way is a chain rebuilt - bounded in its turn - while the cost of being
+     * wrong the other way is the password of the backend in the server error log.
+     */
+    private static boolean holdsCredentials(Throwable failure, String connectionString) {
+        final Deque<Throwable> pending = new ArrayDeque<>();
+        final Set<Throwable> visited = Collections.newSetFromMap(new IdentityHashMap<Throwable, Boolean>());
+        enqueue(pending, visited, failure);
+        for (int links = 0; !pending.isEmpty(); links++) {
+            if (links >= MAX_CHAIN_LENGTH) {
+                return true;
+            }
+            final Throwable t = pending.poll();
+            final String message = t.getMessage();
+            if (message != null && !message.equals(redact(message, connectionString))) {
+                return true;
+            }
+            if (t instanceof SQLException) {
+                enqueue(pending, visited, ((SQLException) t).getNextException());
+            }
+            enqueue(pending, visited, t.getCause());
+        }
+        return false;
+    }
+
+    // By identity rather than by equals(): a link of a chain carries a cause and a next exception
+    // both, and a driver is free to make the two the same failure. Enqueued twice, a chain of
+    // those fans out into a copy of itself at every step and spends the budget of a walk on links
+    // it has already looked at - five levels of one are enough to exhaust MAX_CHAIN_LENGTH.
+    private static void enqueue(Deque<Throwable> pending, Set<Throwable> visited, Throwable t) {
+        if (t != null && visited.add(t)) {
+            pending.add(t);
+        }
+    }
+
+    // The budget counts the links this rebuilds, the way holdsCredentials() counts the ones it
+    // visits - not how deep it has gone. A link of a chain carries a cause and a next exception
+    // both, and a driver is free to make them the same failure, so a bound on depth alone leaves
+    // room for a chain that fans out into two copies of itself at every step.
+    private static SQLException redactedCopy(SQLException e, String connectionString, int[] budget) {
+        budget[0]--;
+        final SQLException copy =
+            new SQLException(redact(e.getMessage(), connectionString), e.getSQLState(), e.getErrorCode());
+        copy.setStackTrace(e.getStackTrace());
+        if (e.getNextException() != null) {
+            copy.setNextException(budget[0] > 0
+                ? redactedCopy(e.getNextException(), connectionString, budget) : droppedTail());
+        }
+        if (e.getCause() != null) {
+            copy.initCause(budget[0] > 0 ? redactedLink(e.getCause(), connectionString, budget) : droppedTail());
+        }
+        return copy;
+    }
+
+    // What stands where the budget ran out. Without it the same failure logs its root cause when
+    // the url of the backend has no password in it and loses it without a word when it has, which
+    // is a report of a connect nobody can read against a report of one they can.
+    private static SQLException droppedTail() {
+        return new SQLException("the rest of this failure was left out: a chain of more than "
+            + MAX_CHAIN_LENGTH + " links is rebuilt only that far");
+    }
+
+    // A link that is no SQLException keeps its class name in the message: its type is not one this
+    // can rebuild, and the name of the failure is what a reader of the log is after.
+    private static Throwable redactedLink(Throwable t, String connectionString, int[] budget) {
+        if (t instanceof SQLException) {
+            return redactedCopy((SQLException) t, connectionString, budget);
+        }
+        budget[0]--;
+        final Throwable copy = new Throwable(t.getClass().getName()
+            + (t.getMessage() == null ? "" : ": " + redact(t.getMessage(), connectionString)));
+        copy.setStackTrace(t.getStackTrace());
+        if (t.getCause() != null) {
+            copy.initCause(budget[0] > 0 ? redactedLink(t.getCause(), connectionString, budget) : droppedTail());
+        }
+        return copy;
+    }
+
+    /**
+     * A message of a driver as it may be logged. A driver is free to put the connection string it
+     * was handed into it - the jdk itself does, "No suitable driver found for " + url, which is
+     * what the ordinary oracle misconfiguration of a driver jar left out of lib/extensions arrives
+     * as - and that connection string is where the credentials of this backend live.
+     * What it cannot answer for is a driver quoting back a part of a url it failed to parse:
+     * a whole credential is replaced, a fragment of one is not.
+     */
+    static String redact(String message, String connectionString) {
+        if (message == null || message.isEmpty()) {
+            return message;
+        }
+        String redacted = message.replace(connectionString, safeUrl(connectionString));
+        // The parameter before the values: a password blanked here is one the loop below no longer
+        // finds, while the other way round a "<credentials hidden>" standing behind a "password="
+        // would be cut in half by a pattern that ends its value at the first space.
+        redacted = SECRET_PARAMETER.matcher(redacted).replaceAll("$1=***");
+        for (final String secret : secretsOf(connectionString)) {
+            redacted = secretPattern(secret).matcher(redacted)
+                .replaceAll(Matcher.quoteReplacement(CREDENTIALS_HIDDEN));
+        }
+        return redacted;
+    }
+
+    /**
+     * A secret as it is looked for in a message: the value itself, wherever it does not stand
+     * inside a longer run of letters and digits. A password is free to be one character long, and
+     * a bare one of those is a substring of half the lines a driver writes - a password of "1"
+     * takes "ORA-12541: TNS:no listener" apart into a line nobody can read, and it makes every
+     * failure of that backend one this class believes names the credentials, so the whole chain is
+     * rebuilt as well. A redaction that destroys the diagnostic it protects is the worse of the
+     * two failures. What a driver quotes back is a credential standing on its own - between the
+     * delimiters of a url, or in a sentence of its own - and that is still replaced.
+     */
+    private static Pattern secretPattern(String secret) {
+        final String before = isAlphanumeric(secret.charAt(0)) ? "(?<![A-Za-z0-9])" : "";
+        final String after = isAlphanumeric(secret.charAt(secret.length() - 1)) ? "(?![A-Za-z0-9])" : "";
+        return Pattern.compile(before + Pattern.quote(secret) + after);
+    }
+
+    private static boolean isAlphanumeric(char c) {
+        return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9');
+    }
+
+    /** What of a connection string must not stand in a message: the credentials safeUrl() takes out of it. */
+    private static List<String> secretsOf(String connectionString) {
+        final List<String> secrets = new ArrayList<>();
+        final ConnectDialect dialect = ConnectDialect.of(connectionString);
+        final String separators = dialect == null ? "?;" : String.valueOf(dialect.parameterSeparator);
+        final int scheme = connectionString.indexOf(':', "jdbc:".length()) + 1;
+        if (scheme <= 0) {
+            return secrets;
+        }
+        final int authority = startOfAuthority(connectionString, scheme);
+        if (authority < 0) {
+            final int at = connectionString.indexOf('@', scheme);
+            if (at > scheme) {
+                addSecret(secrets, connectionString.substring(credentialsStart(connectionString, scheme, at), at));
+            }
+        } else {
+            final int end = endOfAuthority(connectionString, authority, separators);
+            for (final String host : connectionString.substring(authority, end).split(",", -1)) {
+                final int at = host.lastIndexOf('@');
+                if (at > 0) {
+                    addSecret(secrets, host.substring(0, at));
+                }
+            }
+        }
+        final Matcher parameter = SECRET_PARAMETER.matcher(connectionString);
+        while (parameter.find()) {
+            addSecret(secrets, parameter.group(3));
+        }
+        return secrets;
+    }
+
+    // The credentials of one host, and the password inside them without the user name in front of
+    // it: a driver quoting a url back names either.
+    private static void addSecret(List<String> secrets, String credentials) {
+        if (credentials.isEmpty()) {
+            return;
+        }
+        secrets.add(credentials);
+        final int password = indexOfAny(credentials, ":/", 0);
+        if (password >= 0 && password + 1 < credentials.length()) {
+            secrets.add(credentials.substring(password + 1));
+        }
+    }
+
+    // The connection string carries the credentials of the backend - JDBCStorage hands the whole
+    // db-directory of the configuration to this class, so the url is the only place they live -
+    // and it is never logged as it stands. Three shapes hold them and all three are taken off: the
+    // "user/password@" in front of an oracle descriptor; the userinfo of an authority, one per
+    // host of it, since a url of Connector/J gives every host credentials of its own
+    // ("//u:p@h1:3306,u2:p2@h2:3306"); and the parameters behind their first separator,
+    // "?user=...&password=..." on postgresql, mysql and oracle, ";password=..." on sql server.
+    // What is left is looked over once more: the key-value host syntax of Connector/J puts a
+    // password inside the authority itself ("//address=(host=h)(user=u)(password=p)"), where
+    // neither of the first two shapes stands, so a "password=" of any case is blanked out wherever
+    // it is left standing.
+    //
+    // A password is free to hold either of the delimiters, so neither of them is looked for in the
+    // whole string. The credentials of an oracle url stand between the subprotocol and the first
+    // "@", which is the delimiter of its descriptor, so a "?" of one is part of the password
+    // rather than the start of the parameters. Everywhere else they stand inside the authority,
+    // between "//" and the path behind it, so a "?" of a password is inside them and an "@" of a
+    // parameter value ("?user=u@example.com") is not mistaken for the end of them: the host
+    // survives in the message either way.
+    //
+    // And a url none of this took apart is not logged past its subprotocol. An "@" left standing
+    // anywhere but where the credentials of an oracle url ended is one this did not recognize - a
+    // password holding a "/" inside an authority, a quoted one holding an "@" - and the host of a
+    // stall report is worth less than a password in the server log.
+    static String safeUrl(String connectionString) {
+        final ConnectDialect dialect = ConnectDialect.of(connectionString);
+        final String separators = dialect == null ? "?;" : String.valueOf(dialect.parameterSeparator);
+        final int scheme = connectionString.indexOf(':', "jdbc:".length()) + 1; // the end of "jdbc:<subprotocol>:"
+        if (scheme <= 0) {
+            return CREDENTIALS_HIDDEN;
+        }
+        final String stripped = stripCredentials(connectionString, scheme, separators);
+        final int parameters = indexOfAny(stripped, separators, scheme);
+        final String url = parameters < 0 ? stripped : stripped.substring(0, parameters);
+        final String redacted = SECRET_PARAMETER.matcher(url).replaceAll("$1=***");
+        // an "@" standing anywhere but where the credentials of an oracle url ended is one this
+        // did not recognize - a password holding a "/" inside an authority, a quoted one holding
+        // an "@" - and the host of a stall report is worth less than a password in the server log
+        if (redacted.lastIndexOf('@') > endOfRecognizedCredentials(connectionString, scheme)) {
+            return redacted.substring(0, scheme) + CREDENTIALS_HIDDEN;
+        }
+        return parameters < 0 ? redacted
+            : redacted + identifyingParameters(stripped.substring(parameters), dialect);
+    }
+
+    /**
+     * The parameters worth keeping in a message: the ones naming the database rather than whoever
+     * connects to it. Two backends of one host answer to the same url up to their parameters, and
+     * a stall report that cannot tell them apart is a stall report of neither. Everything else is
+     * dropped rather than looked at - a name this does not know is a name free to carry a secret.
+     */
+    private static String identifyingParameters(String parameters, ConnectDialect dialect) {
+        final char separator = dialect == null ? ';' : dialect.parameterSeparator;
+        final StringBuilder kept = new StringBuilder();
+        for (final String parameter : parameters.split("[?&;]")) {
+            final int equals = parameter.indexOf('=');
+            if (equals > 0
+                && IDENTIFYING_PARAMETERS.contains(parameter.substring(0, equals).toLowerCase(Locale.ROOT))) {
+                kept.append(kept.length() == 0 || separator != '?' ? separator : '&').append(parameter);
+            }
+        }
+        return kept.toString();
+    }
+
+    private static String stripCredentials(String url, int scheme, String separators) {
+        final int authority = startOfAuthority(url, scheme);
+        if (authority < 0) {
+            // no authority: the credentials of an oracle url stand between the subprotocol and the
+            // first "@", which is the delimiter of the descriptor behind it - a password holding
+            // an "@" of its own has to be quoted for the driver itself
+            final int at = url.indexOf('@', scheme);
+            return at < 0 ? url : url.substring(0, credentialsStart(url, scheme, at)) + url.substring(at);
+        }
+        final int end = endOfAuthority(url, authority, separators);
+        return url.substring(0, authority) + withoutUserinfo(url.substring(authority, end)) + url.substring(end);
+    }
+
+    /**
+     * Where the credentials of a url that names no authority start: behind the token naming the
+     * kind of driver, which stands in front of them ("jdbc:oracle:thin:user/pw@...") and is worth
+     * keeping - thin against oci is a first question of an oracle connect. The token is the one
+     * right behind the subprotocol rather than the last one in front of the "@", since a password
+     * is free to hold a ":" of its own.
+     */
+    private static int credentialsStart(String url, int scheme, int at) {
+        final int driverType = url.indexOf(':', scheme);
+        return driverType >= 0 && driverType < at ? driverType + 1 : scheme;
+    }
+
+    /**
+     * The last position a stripped url may still carry an "@" at: where the credentials of an
+     * oracle url ended, since the "@" is the delimiter of the descriptor behind them and stays.
+     * An authority keeps none of its own - every userinfo of it is taken off, delimiter included.
+     */
+    private static int endOfRecognizedCredentials(String url, int scheme) {
+        final int at = url.indexOf('@', scheme);
+        return startOfAuthority(url, scheme) < 0 && at > scheme ? credentialsStart(url, scheme, at) : scheme;
+    }
+
+    /**
+     * Where the hosts of a url of this shape start, or -1 for a url that names no authority. The
+     * subprotocol is free to name the kind of connection in front of it - "jdbc:mysql:replication://"
+     * - so the "//" is looked for rather than expected right behind the subprotocol. An "@" in
+     * front of it belongs to an oracle url ("jdbc:oracle:thin:user/pw@//host"), whose credentials
+     * stand where an authority has no place for them.
+     */
+    private static int startOfAuthority(String url, int scheme) {
+        final int slashes = url.indexOf("//", scheme);
+        if (slashes < 0 || url.lastIndexOf('@', slashes) >= scheme) {
+            return -1;
+        }
+        // ... and so does a "/" in front of them: it is what separates the credentials of an
+        // oracle url ("thin:user/pw@..."), so a password holding a "//" of its own would start an
+        // authority inside itself. The "@" ending the credentials stands behind that point, the
+        // userinfo taken off is a piece of the password rather than the whole of it, and the "@"
+        // the guard of safeUrl() looks for is gone with it - leaving the user name and the head of
+        // the password in the message of a stall.
+        final int slash = url.indexOf('/', scheme);
+        return slash >= 0 && slash < slashes ? -1 : slashes + 2;
+    }
+
+    /**
+     * Where the hosts of an authority end: at the path behind them - a password holds a "?" more
+     * readily than a "/" - or at the first parameter of a url that has no path.
+     */
+    private static int endOfAuthority(String url, int authority, String separators) {
+        final int path = url.indexOf('/', authority);
+        if (path >= 0) {
+            return path;
+        }
+        final int parameter = indexOfAny(url, separators, authority);
+        return parameter < 0 ? url.length() : parameter;
+    }
+
+    /** The hosts of an authority, each of them without the credentials a url may give it. */
+    private static String withoutUserinfo(String authority) {
+        final StringBuilder hosts = new StringBuilder();
+        final String[] split = authority.split(",", -1);
+        for (int i = 0; i < split.length; i++) {
+            if (i > 0) { // by the position rather than by what is in hand: a first host may be empty
+                hosts.append(',');
+            }
+            final int at = split[i].lastIndexOf('@');
+            hosts.append(at < 0 ? split[i] : split[i].substring(at + 1));
+        }
+        return hosts.toString();
+    }
+
+    private static int indexOfAny(String url, String separators, int from) {
+        int found = -1;
+        for (int i = 0; i < separators.length(); i++) {
+            final int at = url.indexOf(separators.charAt(i), from);
+            if (at >= 0 && (found < 0 || at < found)) {
+                found = at;
+            }
+        }
+        return found;
+    }
+
+    private static void closeQuietly(Connection con) {
+        try {
+            con.close();
+        } catch (SQLException e) {
+            // ignore: it is on its way out anyway
         }
     }
 
@@ -153,8 +1433,21 @@
 
     @Override
     public void close() throws SQLException {
-        rollback();
-        cached.get(connectionString).add(this);
+        try {
+            rollback();
+        } catch (SQLException e) {
+            // A connection that cannot be rolled back must not be handed to the next borrower -
+            // and must not be dropped on the floor either: nothing else holds it any more.
+            closeQuietly(parent);
+            throw e;
+        }
+        if (!poolable) {
+            closeQuietly(parent);
+            return;
+        }
+        // Returned to the end the next borrow takes it from, so that the pool keeps reusing its
+        // hottest connections rather than cycling through every one it ever opened.
+        cached.get(connectionString).addFirst(this);
     }
 
     @Override
diff --git a/opendj-server-legacy/src/main/java/org/opends/server/backends/jdbc/JDBCStorage.java b/opendj-server-legacy/src/main/java/org/opends/server/backends/jdbc/JDBCStorage.java
index 599a0f7..a63eb14 100644
--- a/opendj-server-legacy/src/main/java/org/opends/server/backends/jdbc/JDBCStorage.java
+++ b/opendj-server-legacy/src/main/java/org/opends/server/backends/jdbc/JDBCStorage.java
@@ -42,6 +42,7 @@
 import java.util.*;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.TimeUnit;
+import java.util.function.Predicate;
 
 import static org.opends.server.backends.pluggable.spi.StorageUtils.addErrorMessage;
 import static org.opends.server.util.StaticUtils.stackTraceToSingleLineString;
@@ -73,8 +74,17 @@
 	/** Upper bound the doubled delay is capped at, in milliseconds. */
 	private static final double MAX_SLEEP_ON_RETRY_MS = 1000.0;
 
-	/** Number of {@link Throwable#getCause()} hops walked when classifying a failure, also a guard against a cycle. */
-	private static final int MAX_CAUSE_HOPS = 16;
+	/**
+	 * Number of links walked when classifying a failure, also a guard against a chain long enough to matter. One
+	 * number for three chains at once - the causes, the next exceptions and the suppressed exceptions are walked
+	 * together and counted together - so it is set well above the depth a wrapped failure of this backend reaches:
+	 * mssql-jdbc chains every error of one message it received through {@code setNextException}, and a budget spent
+	 * on those would never reach the cause the wrapper carries.
+	 */
+	private static final int MAX_CHAIN_LINKS = 64;
+
+	/** The budget of {@link #failureScope}, which walks to the end of the chains: see the comment above it. */
+	private static final int EVERY_LINK = Integer.MAX_VALUE;
 
 	/** SQL Server error number of the transaction picked as the deadlock victim: "Rerun the transaction". */
 	private static final int MSSQL_DEADLOCK_VICTIM = 1205;
@@ -103,6 +113,21 @@
 	private static final Set<String> NON_REPLAYABLE_ROLLBACK_STATES =
 			Collections.unmodifiableSet(new HashSet<>(Arrays.asList("40002", "40003")));
 
+	/** SQLState class 08, connection exception: the connection is gone, whatever the statement asked for. */
+	private static final String CONNECTION_FAILURE_CLASS = "08";
+
+	/**
+	 * The states outside class 08 that also say the connection is gone rather than the statement wrong. PostgreSQL
+	 * announces the connection it is about to drop as 57P01 (admin_shutdown - a pg_terminate_backend of an idle
+	 * connection reaper, or a shutdown of the server), 57P02 (crash_shutdown) or 57P03 (cannot_connect_now), and
+	 * only the next use of that connection is reported as class 08. They are the states of the list HikariCP
+	 * evicts a connection on that a driver of this backend reports: of the rest, JZ0C0 and JZ0C1 belong to a Sybase
+	 * driver this backend is not used with, 01002 is a disconnect none of these four drivers reports, and 0A000 is
+	 * the standard "feature not supported", which says nothing about the connection at all.
+	 */
+	private static final Set<String> CONNECTION_FAILURE_STATES =
+			Collections.unmodifiableSet(new HashSet<>(Arrays.asList("57P01", "57P02", "57P03")));
+
 	private JDBCBackendCfg config;
 
 	public JDBCStorage(JDBCBackendCfg cfg, ServerContext serverContext) {
@@ -156,11 +181,23 @@
 		return CachedConnection.getConnection(config.getDBDirectory());
 	}
 
+	/**
+	 * Borrows a connection the pool validates whatever the alive window of
+	 * {@link CachedConnection#ALIVE_BYPASS_PROPERTY} says, for the borrows this class compensates a dropped
+	 * connection on in no other way: {@link #open(AccessMode)}, {@link #removeStorageFiles()} and the importer
+	 * issue their statements far from the borrow, and the open issues none at all, so a connection dropped inside
+	 * the window would surface out of the rollback that releases it. One round trip on a path taken once per open,
+	 * per import or per removal buys back exactly what master did on every borrow.
+	 */
+	Connection getValidatedConnection() throws Exception {
+		return CachedConnection.getConnection(config.getDBDirectory(), false);
+	}
+
 
 	AccessMode accessMode=AccessMode.READ_ONLY;
 	@Override
 	public void open(AccessMode accessMode) throws Exception {
-		try (final Connection con=getConnection()) {
+		try (final Connection con=getValidatedConnection()) {
 			this.accessMode = accessMode;
 			storageStatus = StorageStatus.working();
 		}
@@ -596,42 +633,25 @@
 		SESSION
 	}
 
-	// What a failed stamp says about trying again. Both chains of the failure are walked: a driver
-	// reports the vendor error of a rejected statement as the next exception of a generic one at
-	// least as often as it reports it as the cause, and reading only one of the two would classify
-	// a lock timeout as a rejection, which leaves the tree unstamped for the life of the backend
-	// over a moment of contention.
+	// What a failed stamp says about trying again. Every chain of the failure is walked, by the walk
+	// every other classifier of this class uses: a driver reports the vendor error of a rejected
+	// statement as the next exception of a generic one at least as often as it reports it as the
+	// cause, the statement of a try-with-resources carries what its close() saw as a suppressed
+	// exception, and reading fewer of them than the others do would classify a connection that broke
+	// as a rejection - which leaves the tree unstamped for the life of the backend. Walked to its end
+	// rather than to MAX_CHAIN_LINKS: the seen set already terminates it, and the verdict weakens
+	// under truncation rather than simply going unnoticed - a SESSION past the budget would come back
+	// as TREE. The strongest verdict wins, so it is asked for in that order.
 	static FailureScope failureScope(Throwable failure, Dialect dialect) {
-		FailureScope scope=FailureScope.TREE;
-		final Deque<Throwable> pending=new ArrayDeque<>();
-		final Set<Throwable> seen=Collections.newSetFromMap(new IdentityHashMap<Throwable,Boolean>());
-		if (failure!=null) {
-			pending.push(failure);
+		if (firstLinkMatching(failure, WITH_THE_RELEASE, EVERY_LINK,
+				e -> scopeOf(e, dialect)==FailureScope.SESSION)!=null) {
+			return FailureScope.SESSION;
 		}
-		while (!pending.isEmpty()) {
-			final Throwable e=pending.pop();
-			if (!seen.add(e)) { // a driver that chains an exception back to itself must not loop this walk
-				continue;
-			}
-			if (e.getCause()!=null) {
-				pending.push(e.getCause());
-			}
-			if (!(e instanceof SQLException)) {
-				continue;
-			}
-			final SQLException sqlException=(SQLException) e;
-			if (sqlException.getNextException()!=null) {
-				pending.push(sqlException.getNextException());
-			}
-			final FailureScope found=scopeOf(sqlException, dialect);
-			if (found==FailureScope.SESSION) { // nothing further down either chain can weaken this one
-				return FailureScope.SESSION;
-			}
-			if (found==FailureScope.MOMENT) {
-				scope=FailureScope.MOMENT;
-			}
+		if (firstLinkMatching(failure, WITH_THE_RELEASE, EVERY_LINK,
+				e -> scopeOf(e, dialect)==FailureScope.MOMENT)!=null) {
+			return FailureScope.MOMENT;
 		}
-		return scope;
+		return FailureScope.TREE;
 	}
 
 	// What one exception of the chain says on its own.
@@ -794,7 +814,7 @@
 		}
 		final Set<TreeName> trees=listTrees();
 		if (!trees.isEmpty()) {
-			try (final Connection con = getConnection()) {
+			try (final Connection con = getValidatedConnection()) {
 				try {
 					for (final TreeName treeName : trees) {
 						try (final PreparedStatement statement = con.prepareStatement("drop table " + getTableName(treeName))) {
@@ -834,11 +854,43 @@
 	 * counters in instance fields that no attempt resets, so a replay reports twice the entry count of the backend.
 	 * Both are reachable while the server is online, since an export holds no more than a shared backend lock.
 	 * A conflict therefore fails the read here, exactly as it did before the retry of {@link #write} was added.
+	 * <p>
+	 * A connection the database dropped is not replayed either, for the same reason - but it is reported to the
+	 * pool, which cannot notice one on its own: a borrow inside the alive window of
+	 * {@link CachedConnection#ALIVE_BYPASS_PROPERTY} asks the database nothing, so the statement that broke is the
+	 * only place the drop is ever seen.
 	 */
 	@Override
 	public <T> T read(ReadOperation<T> readOperation) throws Exception {
-		try(final Connection con=getConnection()) {
-			return readOperation.run(new ReadableTransactionImpl(con));
+		//borrowed outside the try: a connect the pool could not make says nothing about the connections it
+		//holds - mysql reports a server at its connection limit as 08004, which is class 08 like a connection
+		//that broke - and distrusting the pool over it would validate every borrow under the very load the
+		//window exists for, against a server already refusing connections
+		final Connection con=getConnection();
+		boolean dropped=false;
+		try (con) {
+			try {
+				return readOperation.run(new ReadableTransactionImpl(con));
+			} catch (Exception e) {
+				//asked while this read still owns the connection: once the release below has returned it to
+				//the pool, another borrow may hold it and the driver would be answering about that one
+				dropped=isConnectionFailure(e,con);
+				if (dropped) {
+					//told before the release rather than after it: a rollback that never reaches the server -
+					//which is what pgjdbc does with a transaction it left IDLE - leaves the connection poolable,
+					//so the release puts the dropped connection back at the head of the deque, and a borrow
+					//racing the distrust would be handed it unvalidated
+					distrustPool();
+				}
+				throw e;
+			}
+		} catch (Exception e) {
+			//also the release of the connection: its rollback is the one round trip a read that found
+			//nothing makes, so it can be the only place a drop is ever seen
+			if (!dropped && isConnectionFailure(e)) {
+				distrustPool();
+			}
+			throw e;
 		}
 	}
 
@@ -864,6 +916,13 @@
 	 * Only the operation itself is replayed: a failure of {@link #getConnection()} or of the implicit
 	 * {@link Connection#close()} - which returns the connection to the pool after a rollback - leaves the loop, so
 	 * that a completed write is never replayed because releasing its connection failed.
+	 * <p>
+	 * A connection the database dropped is replayed as well, on a connection the next attempt borrows of its own.
+	 * That is what makes the alive window of {@link CachedConnection#ALIVE_BYPASS_PROPERTY} safe to leave on: a
+	 * connection handed out unvalidated and found dead costs an attempt rather than the operation, and a write of
+	 * the replication replay - which records a failed operation as applied and advances the server state past it,
+	 * see #889 - never sees it. Only while nothing of the attempt may have been committed yet, though: see
+	 * {@link #replayReason(Throwable, String, boolean, boolean, boolean)}.
 	 */
 	@Override
 	public void write(WriteOperation writeOperation) throws Exception {
@@ -871,35 +930,93 @@
 		for (int attempt=1;;attempt++) {
 			Exception failure=null;
 			String driver=null;
-			try (final Connection con=getConnection()) {
+			boolean committing=false;
+			boolean dropped=false;
+			boolean partlyCommitted=false;
+			//borrowed outside the try, for the reason read() borrows outside it: a connect the pool could not
+			//make is not a connection of this pool that broke, and it leaves the loop as it always did
+			final Connection con=getConnection();
+			try (con) {
 				driver=driverNameOf(con);
 				final WriteableTransactionTransactionImpl txn=new WriteableTransactionTransactionImpl(con);
 				try {
 					writeOperation.run(txn);
+					committing=true;
 					con.commit();
 					return;
 				} catch (Exception e) {
 					try {
 						con.rollback();
-					} catch (SQLException ex) {}
+					} catch (SQLException ex) {
+						//joined to the failure rather than dropped: a rollback issued on a connection the
+						//database dropped is often the first place - and on a driver that reports a killed
+						//session as a plain vendor error, the only place - the drop is stated outright, and
+						//every classifier below reads the chains of this failure
+						e.addSuppressed(ex);
+					}
+					//asked while this attempt still owns the connection: the release below returns it to the
+					//pool, and the driver would then be answering about whichever borrow holds it next
+					dropped=isConnectionFailure(e,con);
+					if (dropped) {
+						//told before the release rather than after it, for the reason read() tells it there: a
+						//rollback that never reached the server leaves the connection poolable, so the release
+						//returns the dropped connection to the head of the deque, where a borrow racing this
+						//would be handed it unvalidated
+						distrustPool();
+					}
 					//rethrown, so that a failure of the implicit close() is suppressed into the failure being
 					//replayed rather than replacing it
 					failure=e;
 					throw e;
 				} finally { // the comment connection lives no longer than the trees it stamped, and no longer
 					// than the attempt that opened it: a replay stamps on a session of its own
-					txn.stampSession.close();
+					partlyCommitted=txn.partlyCommitted;
+					try {
+						txn.stampSession.close();
+					} catch (RuntimeException e) {
+						//the stamp is a diagnostic aid and must not become the outcome of the write: an unchecked
+						//throw out of a driver's close() would otherwise replace the failure being unwound (JLS
+						//14.20.2) - the very one the replay is decided on and the only one that says what went
+						//wrong - or turn a transaction that has just committed into a failure of its own
+						if (failure!=null) {
+							failure.addSuppressed(e);
+						} else {
+							logger.trace(LocalizableMessage.raw("jdbc: unable to close the comment connection: %s",
+									stackTraceToSingleLineString(e)));
+						}
+					}
 				}
 			} catch (Exception e) {
-				//anything the operation did not throw comes from getConnection() or from the implicit close(),
-				//which returns the connection to the pool: neither belongs to the replayed region
+				//anything the operation did not throw comes from around it - the name of the driver, the
+				//transaction, or the implicit close() that returns the connection to the pool: none of them
+				//belongs to the replayed region
 				if (e!=failure) {
+					//a drop reported by the release of the connection still has to reach the pool, which has no
+					//other way of hearing of it. Only the chains of the failure can be asked for it now: the
+					//connection has been released, and whether it is closed is no longer this attempt's answer
+					if (isConnectionFailure(e)) {
+						distrustPool();
+					}
 					throw e;
 				}
 			}
+			//a drop the release of the connection reported still has to reach the pool, which has no other way
+			//of hearing of it. It is suppressed into the failure being unwound (JLS 14.20.3.1) rather than
+			//replacing it, which is what leaves e==failure and skips the branch above - and it is the very
+			//evidence replayReason() replays the attempt on, so the pool must not be told less than the loop
+			//acts on. The drop of the operation itself was reported before the release, above
+			if (!dropped && isConnectionFailure(failure)) {
+				distrustPool();
+			}
+			//Two questions, asked apart: what the failure is - which replayReason() answers, and which is the
+			//only place that reads committing, partlyCommitted and dropped - and whether another attempt is
+			//still allowed, which is the attempt count and the window of #903. Neither subsumes the other: a
+			//dropped connection is worth replaying and carries no conflict class, while a conflict past both
+			//bounds is not replayed however plainly it is one
+			final String reason=replayReason(failure,driver,committing,partlyCommitted,dropped);
 			//nanoTime()-startedAt is the overflow safe form of the elapsed time
 			final long elapsedNanos=nanoTime()-startedAt;
-			if (!replayable(attempt, elapsedNanos, failure, driver)) {
+			if (reason==null || !replayableWithin(attempt, elapsedNanos, failure, driver)) {
 				throw failure;
 			}
 			//logged rather than silently absorbed, so that a deployment retrying most of its writes stays observable;
@@ -910,13 +1027,13 @@
 			//engines report a deadlock in a few of them and whole seconds would read "0" for most of a burst; and
 			//the one line that replays past its own window says so, rather than reading as a bound not honoured
 			logger.warn(LocalizableMessage.raw(
-					"jdbc: replaying the transaction after a %s conflict, attempt %d of %d, %d ms elapsed of the %d ms window%s: %s",
-					conflictOf(failure, driver), attempt, MAX_RETRIES, TimeUnit.NANOSECONDS.toMillis(elapsedNanos),
+					"jdbc: replaying the transaction after %s, attempt %d of %d, %d ms elapsed of the %d ms window%s: %s",
+					reason, attempt, MAX_RETRIES, TimeUnit.NANOSECONDS.toMillis(elapsedNanos),
 					TimeUnit.NANOSECONDS.toMillis(RETRY_WINDOW_NANOS),
 					elapsedNanos>=RETRY_WINDOW_NANOS ? " (the first replay, granted past it)" : "",
-					conflictSummary(failure)));
+					conflictSummary(failure, driver)));
 			if (logger.isTraceEnabled()) {
-				logger.trace("jdbc: the conflict being replayed was %s", stackTraceToSingleLineString(failure));
+				logger.trace("jdbc: the failure being replayed was %s", stackTraceToSingleLineString(failure));
 			}
 			try {
 				//randomized to spread the retries of the transactions that collided, growing to outlast contention
@@ -940,6 +1057,168 @@
 		return System.nanoTime();
 	}
 
+	/**
+	 * Why the operation of a {@link #write} is worth replaying, as the noun phrase the message reporting the replay
+	 * names - or null for a failure this loop must not repeat.
+	 * <p>
+	 * A transaction conflict is replayable whichever phase reported it: the engine rolled the transaction back
+	 * before it answered. It is read from the failure of the operation only, never from the release of the
+	 * connection - see {@link #isRetryableConflict} - since the release runs after the outcome was decided and
+	 * cannot make that claim for it. A connection the database dropped is replayable only while the transaction
+	 * had not been committed yet. A drop reported by {@code commit()} leaves the outcome unknown - the server may
+	 * have committed and died before the answer reached us - and replaying a write that in fact committed applies
+	 * it twice, which is the very reason 40003 is one of {@link #NON_REPLAYABLE_ROLLBACK_STATES}.
+	 * <p>
+	 * Nothing is replayable once the attempt has committed part of its own work, whatever the failure says. The DDL
+	 * of {@link WriteableTransactionTransactionImpl#openTree} and {@link WriteableTransactionTransactionImpl#deleteTree}
+	 * commits inside {@link WriteOperation#run}, and mysql and oracle commit before a DDL statement whether asked
+	 * to or not, so the attempt no longer rolls back as a whole - and {@link WriteOperation} is only idempotent in
+	 * the database. {@code RootContainer.open} opens and registers every entry container of every base DN in one
+	 * write: replayed after the trees of the first base DN were created and committed, it registers that base DN a
+	 * second time and fails with ERR_ENTRY_CONTAINER_ALREADY_REGISTERED, which masks the failure that caused the
+	 * replay and leaves the indexes of the previous attempt behind with their configuration listeners.
+	 *
+	 * @param committing whether the failure was reported by {@code commit()}, which leaves the outcome unknown
+	 * @param partlyCommitted whether the attempt committed part of its work before it failed
+	 * @param connectionClosed whether the driver closed the connection under the failure - evidence no SQLState
+	 * carries on mssql-jdbc, which reports a killed session as S0001 and closes the connection behind it
+	 */
+	static String replayReason(Throwable failure, String driver, boolean committing, boolean partlyCommitted,
+			boolean connectionClosed) {
+		if (partlyCommitted) {
+			return null;
+		}
+		if (isRetryableConflict(failure, driver)) {
+			return "a conflict";
+		}
+		if (!committing && (connectionClosed || isConnectionFailure(failure))) {
+			return "a connection the database dropped";
+		}
+		return null;
+	}
+
+	/**
+	 * Whether a failure says the connection is gone rather than the statement rejected, asked of the failure and of
+	 * the connection it was raised on. A driver is not required to say so in a SQLState: mssql-jdbc reports a
+	 * session killed by {@code KILL}, by the resource governor or by an availability group transition as error 596,
+	 * 3980, 10054, 18456 or 4060, and {@code generateStateCode} maps none of them - with xopenStates off, which is
+	 * its default, every one of them comes out as {@code "S"+errorState}, measured as S0001. What the driver does
+	 * do is close the connection for any error of severity 20 and above, before it throws.
+	 * <p>
+	 * Asked only while the operation that failed still owns the connection: a released one is back in the pool and
+	 * may already have been handed to another borrow, whose state it would then be answering about.
+	 */
+	static boolean isConnectionFailure(Throwable failure, Connection con) {
+		return isConnectionFailure(failure) || isClosed(con);
+	}
+
+	/** Whether the driver reports the connection as closed; one that cannot answer is taken as closed. */
+	private static boolean isClosed(Connection con) {
+		try {
+			return con.isClosed();
+		} catch (SQLException e) {
+			return true;
+		}
+	}
+
+	/**
+	 * Whether a failure says the connection is gone rather than the statement rejected: the database dropped it,
+	 * restarted, failed over, or the network did.
+	 * <p>
+	 * Both chains of the failure are walked, for the reason {@link #failureScope} walks both: a driver reports the
+	 * error that says what happened as the next exception of a generic one at least as often as it reports it as
+	 * the cause, and mssql-jdbc chains every error of a message it received that way. The suppressed exceptions are
+	 * walked with them, since the rollback and the release of a connection report a drop there - a write whose
+	 * operation failed for its own reasons carries the drop of its {@code close()} as a suppressed exception (JLS
+	 * 14.20.3.1) rather than as a cause. The walk starts at the failure this class was handed because it reaches it
+	 * wrapped in a {@link StorageRuntimeException}, and a caller such as {@code EntryContainer.addEntry} may wrap
+	 * it once more.
+	 */
+	static boolean isConnectionFailure(Throwable failure) {
+		return firstLinkMatching(failure, WITH_THE_RELEASE, JDBCStorage::saysTheConnectionIsGone)!=null;
+	}
+
+	/**
+	 * Whether {@link #firstLinkMatching} reads the suppressed exceptions along with the causes and the next
+	 * exceptions. They are where the release of the connection reports what it saw - a rollback that failed as the
+	 * attempt was unwound is suppressed into the failure being unwound (JLS 14.20.3.1) - so a question about the
+	 * connection is asked of them, and a question about what the engine did with the transaction is not: the
+	 * release runs after the outcome was decided, and cannot speak for it.
+	 */
+	private static final boolean WITH_THE_RELEASE=true;
+	private static final boolean WITHOUT_THE_RELEASE=false;
+
+	/**
+	 * The first {@link SQLException} of the chains of a failure that answers the given question, or null where none
+	 * does. Every classifier of this class walks the failure this way, so that none of them reads a chain the others
+	 * act on: what makes a write replayable must also be what the pool is told about and what the replay logs.
+	 */
+	private static SQLException firstLinkMatching(Throwable failure, boolean withTheRelease,
+			Predicate<SQLException> matches) {
+		return firstLinkMatching(failure, withTheRelease, MAX_CHAIN_LINKS, matches);
+	}
+
+	/** The walk above, with the number of links it is allowed to look at. */
+	private static SQLException firstLinkMatching(Throwable failure, boolean withTheRelease, int links,
+			Predicate<SQLException> matches) {
+		final Deque<Throwable> pending=new ArrayDeque<>();
+		final Set<Throwable> seen=Collections.newSetFromMap(new IdentityHashMap<Throwable,Boolean>());
+		if (failure!=null) {
+			pending.push(failure);
+		}
+		while (!pending.isEmpty() && seen.size()<links) {
+			final Throwable e=pending.pop();
+			if (!seen.add(e)) { // a driver that chains an exception back to itself must not loop this walk
+				continue;
+			}
+			if (e.getCause()!=null) {
+				pending.push(e.getCause());
+			}
+			if (withTheRelease) {
+				for (final Throwable suppressed : e.getSuppressed()) {
+					pending.push(suppressed);
+				}
+			}
+			if (!(e instanceof SQLException)) {
+				continue;
+			}
+			final SQLException sqlException=(SQLException) e;
+			if (sqlException.getNextException()!=null) {
+				pending.push(sqlException.getNextException());
+			}
+			if (matches.test(sqlException)) {
+				return sqlException;
+			}
+		}
+		return null;
+	}
+
+	/**
+	 * What one exception of the chain says on its own. The types are asked before the SQLState, the way
+	 * {@link #scopeOf} asks them: they are what the JDBC contract gives a driver to say the connection is gone, and
+	 * a driver that raises one of them has said so whatever state it filled in. Oracle reports ORA-03113, ORA-00028
+	 * and ORA-01089 as {@link SQLRecoverableException} and happens to map them to 08006 as well; the type is what
+	 * makes that robust rather than lucky.
+	 */
+	private static boolean saysTheConnectionIsGone(SQLException e) {
+		if (e instanceof SQLRecoverableException || e instanceof SQLNonTransientConnectionException
+				|| e instanceof SQLTransientConnectionException) {
+			return true;
+		}
+		final String state=String.valueOf(e.getSQLState());
+		return state.startsWith(CONNECTION_FAILURE_CLASS) || CONNECTION_FAILURE_STATES.contains(state);
+	}
+
+	/**
+	 * Tells the pool of this backend that the database dropped a connection, so that the ones it still holds from
+	 * before the drop are validated on their next borrow instead of being trusted for the rest of the alive window.
+	 * A dropped connection is rarely alone: a restart, a failover or a network that went away takes every
+	 * connection established before it, and the pool has no other way of hearing about any of them.
+	 */
+	private void distrustPool() {
+		CachedConnection.distrustPool(config.getDBDirectory());
+	}
+
 	/** Returns the randomized delay before the given attempt is replayed, doubling with each attempt up to a cap. */
 	static long retryDelayMillis(int attempt) {
 		final double bound=Math.min(MAX_SLEEP_ON_RETRY_MS, BASE_SLEEP_ON_RETRY_MS * (1 << Math.min(attempt-1, 5)));
@@ -964,12 +1243,16 @@
 	 * Returns the class of the conflict the given failure carries, or {@link Conflict#NONE} if it carries none,
 	 * which is what decides whether replaying the operation can resolve it.
 	 * <p>
-	 * The conflict is looked up along the whole cause chain because it reaches this class wrapped: a deadlock in
-	 * {@code put} arrives as {@code StorageRuntimeException(SQLException)}, and a caller such as
-	 * {@code EntryContainer.addEntry} may wrap it once more. The chain is walked to its end rather than stopped at
-	 * the first conflict found, so that the most specific class in it wins: a wrapper that carries a class 40 state
-	 * of its own but no vendor number would otherwise downgrade the {@link Conflict#AFTER_LOCK_WAIT} of the
-	 * {@link SQLException} it wraps, and hand a wait the engine already bounded a replay it does not need.
+	 * The conflict is looked up along every chain of the failure, for the reason {@link #isConnectionFailure} walks
+	 * them all: it reaches this class wrapped - a deadlock in {@code put} arrives as
+	 * {@code StorageRuntimeException(SQLException)}, and a caller such as {@code EntryContainer.addEntry} may wrap it
+	 * once more - and a driver reports the error that says what happened as the next exception of a generic one at
+	 * least as often as it reports it as the cause. The suppressed links of the release are left out of it, for the
+	 * reason {@link #replayReason} gives: the release runs after the outcome was decided.
+	 * <p>
+	 * The most specific class in those chains wins rather than the first one found: a wrapper that carries a class
+	 * 40 state of its own but no vendor number would otherwise downgrade the {@link Conflict#AFTER_LOCK_WAIT} of
+	 * the {@link SQLException} it wraps, and hand a wait the engine already bounded a replay it does not need.
 	 * <p>
 	 * The standard class 40 states carry the conflict of most engines - 40P01 for PostgreSQL, 40001 for SQL Server
 	 * and for MySQL, whose driver replaces the server side HY000 of a deadlock and of a lock wait timeout with
@@ -984,17 +1267,13 @@
 	 * excluded from that match.
 	 */
 	static Conflict conflictOf(Throwable t, String driver) {
-		Conflict found=Conflict.NONE;
-		for (int hop=0; t!=null && hop<MAX_CAUSE_HOPS; t=t.getCause(), hop++) {
-			if (t instanceof SQLException) {
-				final Conflict conflict=classOf((SQLException) t, driver);
-				if (conflict==Conflict.AFTER_LOCK_WAIT) { // the most specific there is: no later hop refines it
-					return conflict;
-				}
-				found=conflict!=Conflict.NONE ? conflict : found;
-			}
+		// asked for the most specific class first, which is what keeps a bare class 40 state elsewhere in the
+		// chains from downgrading the numbered failure that names a wait the engine had already bounded
+		if (firstLinkMatching(t, WITHOUT_THE_RELEASE, e -> classOf(e, driver)==Conflict.AFTER_LOCK_WAIT)!=null) {
+			return Conflict.AFTER_LOCK_WAIT;
 		}
-		return found;
+		return firstLinkMatching(t, WITHOUT_THE_RELEASE, e -> isConflict(e, driver))!=null
+				? Conflict.PROMPT : Conflict.NONE;
 	}
 
 	/**
@@ -1024,18 +1303,40 @@
 	 * transaction connection, is what would let the window govern both classes and retire this grant.
 	 */
 	static boolean replayable(int attempt, long elapsedNanos, Throwable failure, String driver) {
-		final Conflict conflict=conflictOf(failure, driver);
-		if (conflict==Conflict.NONE || attempt>=MAX_RETRIES) {
+		return conflictOf(failure, driver)!=Conflict.NONE
+				&& replayableWithin(attempt, elapsedNanos, failure, driver);
+	}
+
+	/**
+	 * The bounds half of {@link #replayable}, asked of a failure {@link #replayReason} has already found worth
+	 * replaying. Split from the class half because the two answer different questions and not every replayable
+	 * failure carries a conflict class: a connection the database dropped is replayed on the evidence of the drop,
+	 * and would be refused by a bound that first insisted on a class 40 state.
+	 */
+	static boolean replayableWithin(int attempt, long elapsedNanos, Throwable failure, String driver) {
+		if (attempt>=MAX_RETRIES) {
 			return false;
 		}
 		//the engine asked for the transaction to be rerun after a wait nothing here bounds: no clock denies that
 		//first rerun, since the window it would be measured against was spent by the wait rather than by a replay
-		if (attempt==1 && conflict==Conflict.PROMPT) {
+		if (attempt==1 && conflictOf(failure, driver)==Conflict.PROMPT) {
 			return true;
 		}
 		return elapsedNanos<RETRY_WINDOW_NANOS;
 	}
 
+	/**
+	 * Whether the failure carries a transaction conflict, which is {@link #conflictOf} asked as a yes or no. Read
+	 * without the suppressed exceptions, unlike {@link #isConnectionFailure}: a conflict is replayed whichever
+	 * phase reported it, on the strength of the engine having rolled the transaction back before it answered - and
+	 * the release of the connection runs after the outcome was decided and cannot make that claim. A class 40
+	 * raised there would otherwise replay a transaction commit() left in doubt, which is what the committing
+	 * guard of replayReason() exists to prevent.
+	 */
+	static boolean isRetryableConflict(Throwable t, String driver) {
+		return conflictOf(t, driver)!=Conflict.NONE;
+	}
+
 	private static boolean isConflict(SQLException e, String driver) {
 		final String state=String.valueOf(e.getSQLState());
 		if (state.startsWith("40") && !NON_REPLAYABLE_ROLLBACK_STATES.contains(state)) {
@@ -1051,18 +1352,30 @@
 	}
 
 	/**
-	 * Returns the SQLState and vendor error number of the first {@link SQLException} of the given cause chain, which
-	 * is what identifies a conflict, so that a replay can be logged without a stack trace on every attempt.
+	 * Returns the SQLState and vendor error number of the exception a replay was decided on, so that a replay can be
+	 * logged without a stack trace on every attempt. That line is the only record a replay leaves, so it names the
+	 * link the decision was taken on rather than the first {@link SQLException} of the failure: a write whose
+	 * operation failed for its own reasons and whose release then reported a drop is replayed on the class 08
+	 * suppressed into it, and naming the state of the rejected statement instead would describe a replay that did
+	 * not happen. Falls back to the first SQLException of the failure, and to the failure itself where it carries
+	 * none.
 	 */
-	static String conflictSummary(Throwable failure) {
-		Throwable t=failure;
-		for (int hop=0; t!=null && hop<MAX_CAUSE_HOPS; t=t.getCause(), hop++) {
-			if (t instanceof SQLException) {
-				final SQLException e=(SQLException) t;
-				return "SQLState "+e.getSQLState()+", error "+e.getErrorCode()+": "+e.getMessage();
-			}
+	static String conflictSummary(Throwable failure, String driver) {
+		// asked in the order replayReason() asks it, and of the same chains, so that the line names the link the
+		// decision was taken on rather than one that merely resembles it
+		SQLException named=firstLinkMatching(failure, WITHOUT_THE_RELEASE, e -> isConflict(e, driver));
+		if (named==null) {
+			named=firstLinkMatching(failure, WITH_THE_RELEASE, JDBCStorage::saysTheConnectionIsGone);
 		}
-		return String.valueOf(failure);
+		if (named==null) {
+			// without the release, so that the line names the statement that failed rather than the rollback
+			// behind it: this is the fallback of a replay decided on isClosed(con) alone, where neither chain
+			// carries a verdict, and the walk reaches the suppressed exceptions before the cause
+			named=firstLinkMatching(failure, WITHOUT_THE_RELEASE, e -> true);
+		}
+		return named==null
+			? String.valueOf(failure)
+			: "SQLState "+named.getSQLState()+", error "+named.getErrorCode()+": "+named.getMessage();
 	}
 
 	static final byte[] NULL=new byte[]{(byte)0};
@@ -1143,6 +1456,16 @@
 			}
 		}
 	}
+	/**
+	 * A transaction able to write, unless the storage was opened read-only: then it may open an existing tree and
+	 * read it, and every mutating operation throws {@link ReadOnlyStorageException} instead.
+	 * <p>
+	 * The mode is checked per operation rather than refused here, because {@code RootContainer.open(AccessMode)}
+	 * asks for a write transaction even in read-only mode - that is where it opens the compressed schema and the
+	 * entry containers - so refusing to hand one out failed the offline {@code export-ldif}, {@code verify-index}
+	 * and {@code backendstat} before they read anything (#874). Both other storages of this server already have
+	 * this shape: {@code PDBStorage.ReadOnlyStorageImpl} and {@code CASStorage.TransactionImpl.checkReadOnly()}.
+	 */
 	private final class WriteableTransactionTransactionImpl extends ReadableTransactionImpl implements WriteableTransaction {
 
 		// Shared by every table this transaction stamps: opening a backend opens all its trees,
@@ -1150,12 +1473,61 @@
 		// write() (and by ImporterImpl.close()) when the transaction is done with.
 		final StampSession stampSession=new StampSession();
 
+		/**
+		 * Whether this transaction has committed part of its own work, which takes the attempt out of the
+		 * replay of {@link JDBCStorage#write}: what it did no longer rolls back as a whole, and a
+		 * {@link WriteOperation} is only idempotent in the database.
+		 * <p>
+		 * Raised by {@link #commitStatement} alone, which is what every statement of this transaction that
+		 * commits goes through - never once for a method that may issue one: a catalog read deciding that the
+		 * statement is not needed commits nothing, and a transaction the engine rolled back whole is still worth
+		 * replaying. Which side of the statement the flag goes up on is the engine's answer, see there.
+		 */
+		boolean partlyCommitted;
+
 		public WriteableTransactionTransactionImpl(Connection con) {
 			super(con);
-			if (!accessMode.isWriteable()) {
+			//captured once rather than read per operation: the access mode of the storage is mutable state -
+			//ImporterImpl reopens the storage READ_WRITE under its caller - and a transaction has to keep the mode
+			//it was created with. It also drives isReadOnly, so that a cursor this transaction opens refuses
+			//delete() as well.
+			isReadOnly = !accessMode.isWriteable();
+		}
+
+		void checkReadOnly() {
+			if (isReadOnly) {
 				throw new ReadOnlyStorageException();
 			}
-			isReadOnly = false;
+		}
+
+		/**
+		 * Issues a statement that ends in a commit, raising {@link #partlyCommitted} at the moment the attempt
+		 * stops rolling back as a whole.
+		 * <p>
+		 * mysql and oracle commit before a DDL statement whether asked to or not, so there the work behind it is
+		 * committed by the statement itself and the flag has to be up before it is issued: the statement that
+		 * fails has committed everything before it just as surely as the one that succeeds. postgresql and sql
+		 * server run DDL inside the transaction, and a DML statement commits of its own accord nowhere - one that
+		 * fails there has committed nothing, {@link JDBCStorage#write} rolls the attempt back whole, and a flag
+		 * raised in front of it would take a conflict the engine itself undid out of the replay. On those the
+		 * flag goes up in front of the commit instead, which is the call that leaves the outcome of the
+		 * transaction unknown when it fails.
+		 *
+		 * @param ddl whether the statement is a DDL one, which two of the four engines commit before
+		 */
+		private void commitStatement(String sql, boolean ddl) throws SQLException {
+			partlyCommitted|=ddl && commitsBeforeDdl();
+			try (final PreparedStatement statement=con.prepareStatement(sql)) {
+				execute(statement);
+				partlyCommitted=true; // a commit that fails leaves the outcome unknown, which is no more replayable
+				con.commit();
+			}
+		}
+
+		/** Whether this engine commits the transaction before a DDL statement whether asked to or not. */
+		private boolean commitsBeforeDdl() {
+			final String driverName=driverNameOf(con);
+			return driverName.contains("mysql") || driverName.contains("oracle");
 		}
 
 		boolean isExistsTable(TreeName treeName) {
@@ -1196,10 +1568,17 @@
 		@Override
 		public void openTree(TreeName treeName, boolean createOnDemand) {
 			if (createOnDemand) {
+				checkReadOnly();
+				// Every statement below is a DDL that commits, and each raises partlyCommitted through
+				// commitStatement() rather than once for the method: every one of them is guarded by a
+				// catalog read, so on an existing backend this method issues nothing at all. Raising the
+				// flag for a catalog read that commits nothing would make the whole attempt unreplayable -
+				// the conflict replay of #867 as much as the drop replay, since replayReason() reads the
+				// flag before it asks anything else - and RootContainer.open() opens every tree of every
+				// base DN in a single write, whose first act is one of these.
 				if (!isExistsTable(treeName)) {
-					try (final PreparedStatement statement=con.prepareStatement("create table "+getTableName(treeName)+" ("+getTableDialect()+")")){
-						execute(statement);
-						con.commit();
+					try {
+						commitStatement("create table "+getTableName(treeName)+" ("+getTableDialect()+")", true);
 					}catch (SQLException e) {
 						throw new StorageRuntimeException(e);
 					}
@@ -1208,19 +1587,21 @@
 				final String driverName=driverNameOf(con);
 				final String tableName=getTableName(treeName);
 				if (driverName.contains("postgres")) {
-					try (final PreparedStatement statement=con.prepareStatement("create index if not exists k_"+tableName.substring("opendj_".length())+" on "+tableName+" (k)")){
-						execute(statement);
-						con.commit();
+					try {
+						// asked although postgresql has "create index if not exists": that statement commits
+						// whether it creates anything or not, and this is the engine of every default
+						// deployment - unguarded, it would take every write that opens a tree out of the
+						// conflict replay, RootContainer.open() and its ~25 trees per suffix included
+						if (!isExistsIndex(tableName,"k_"+tableName.substring("opendj_".length()))) {
+							commitStatement("create index if not exists k_"+tableName.substring("opendj_".length())+" on "+tableName+" (k)", true);
+						}
 					}catch (SQLException e) {
 						throw new StorageRuntimeException(e);
 					}
 				}else if (driverName.contains("mysql")) {
 					try {
 						if (!isExistsIndex(tableName,"k_"+tableName.substring("opendj_".length()))) { // mysql has no "create index if not exists"
-							try (final PreparedStatement statement=con.prepareStatement("create index k_"+tableName.substring("opendj_".length())+" on "+tableName+" (k)")){
-								execute(statement);
-								con.commit();
-							}
+							commitStatement("create index k_"+tableName.substring("opendj_".length())+" on "+tableName+" (k)", true);
 						}
 					}catch (SQLException e) {
 						throw new StorageRuntimeException(e);
@@ -1229,10 +1610,7 @@
 					try {
 						// oracle has no "create index if not exists"; unquoted identifiers are stored in uppercase
 						if (!isExistsIndex(tableName.toUpperCase(),"k_"+tableName.substring("opendj_".length()))) {
-							try (final PreparedStatement statement=con.prepareStatement("create index k_"+tableName.substring("opendj_".length())+" on "+tableName+" (k)")){
-								execute(statement);
-								con.commit();
-							}
+							commitStatement("create index k_"+tableName.substring("opendj_".length())+" on "+tableName+" (k)", true);
 						}
 					}catch (SQLException e) {
 						throw new StorageRuntimeException(e);
@@ -1258,9 +1636,9 @@
 		}
 		
 		public void clearTree(TreeName treeName) {
-			try (final PreparedStatement statement=con.prepareStatement("delete from "+getTableName(treeName))){
-				execute(statement);
-				con.commit();
+			checkReadOnly();
+			try { // the commit takes the attempt out of the replay: it commits the delete, and everything before it
+				commitStatement("delete from "+getTableName(treeName), false);
 			}catch (SQLException e) {
 				throw new StorageRuntimeException(e);
 			}
@@ -1268,10 +1646,10 @@
 
 		@Override
 		public void deleteTree(TreeName treeName) {
+			checkReadOnly();
 			if (isExistsTable(treeName)) {
-				try (final PreparedStatement statement = con.prepareStatement("drop table " + getTableName(treeName))) {
-					execute(statement);
-					con.commit();
+				try {
+					commitStatement("drop table " + getTableName(treeName), true);
 				} catch (SQLException e) {
 					throw new StorageRuntimeException(e);
 				}
@@ -1283,6 +1661,7 @@
 
 		@Override
 		public void put(TreeName treeName, ByteSequence key, ByteSequence value) {
+			checkReadOnly();
 			try {
 				upsert(treeName, key, value);
 			} catch (SQLException e) {
@@ -1350,6 +1729,9 @@
 
 		@Override
 		public boolean update(TreeName treeName, ByteSequence key, UpdateFunction f) {
+			//checked before the read, so that a read-only transaction reports the mode rather than the value it
+			//computed being equal to the stored one
+			checkReadOnly();
 			final ByteString oldValue=read(treeName,key);
 			final ByteSequence newValue=f.computeNewValue(oldValue);
 			if (Objects.equals(newValue, oldValue))
@@ -1366,6 +1748,7 @@
 
 		@Override
 		public boolean delete(TreeName treeName, ByteSequence key) {
+			checkReadOnly();
 			try (final PreparedStatement statement=con.prepareStatement("delete from "+getTableName(treeName)+" where h="+hashParam(con)+" and k=?")){
 				statement.setString(1,key2hash.get(ByteBuffer.wrap(key.toByteArray())));
 				statement.setBytes(2,real2db(key.toByteArray()));
@@ -1609,7 +1992,7 @@
 				}
 			}
 			try {
-				con = getConnection();
+				con = getValidatedConnection();
 			}catch (Exception e){
 				throw new StorageRuntimeException(e);
 			}
diff --git a/opendj-server-legacy/src/main/java/org/opends/server/backends/pluggable/VLVIndex.java b/opendj-server-legacy/src/main/java/org/opends/server/backends/pluggable/VLVIndex.java
index 757aa99..ca84641 100644
--- a/opendj-server-legacy/src/main/java/org/opends/server/backends/pluggable/VLVIndex.java
+++ b/opendj-server-legacy/src/main/java/org/opends/server/backends/pluggable/VLVIndex.java
@@ -105,6 +105,7 @@
   /** The storage associated with this index. */
   private final Storage storage;
   private final State state;
+  private final EntryContainer entryContainer;
 
   /**
    * A flag to indicate if this vlvIndex should be trusted to be consistent with the entries tree.
@@ -131,15 +132,8 @@
     }
 
     this.state = state;
+    this.entryContainer = entryContainer;
     this.trusted = state.getIndexFlags(txn, getName()).contains(IndexFlag.TRUSTED);
-    if (!trusted && entryContainer.getHighestEntryID(txn).longValue() == 0)
-    {
-      /*
-       * If there are no entries in the entry container then there is no reason why this vlvIndex
-       * can't be upgraded to trusted.
-       */
-      setTrusted(txn, true);
-    }
 
     this.config.addChangeListener(this);
   }
@@ -163,6 +157,19 @@
   void afterOpen(final WriteableTransaction txn, boolean createOnDemand) throws StorageRuntimeException
   {
     counter.open(txn, createOnDemand);
+    if (createOnDemand && !trusted && entryContainer.isEmpty(txn))
+    {
+      /*
+       * If there are no entries in the entry container then there is no reason why this vlvIndex
+       * can't be upgraded to trusted.
+       *
+       * Guarded by createOnDemand - which is accessMode.isWriteable() - and done here rather than in the
+       * constructor, as DefaultIndex.afterOpen() does: the transaction a read-only container opens is not
+       * allowed to write, so upgrading an untrusted index of an empty backend used to fail the offline tools
+       * on it instead of leaving the flag alone (#874).
+       */
+      setTrusted(txn, true);
+    }
   }
 
   @Override
diff --git a/opendj-server-legacy/src/test/java/org/opends/server/backends/jdbc/CachedConnectionTestCase.java b/opendj-server-legacy/src/test/java/org/opends/server/backends/jdbc/CachedConnectionTestCase.java
new file mode 100644
index 0000000..c98f280
--- /dev/null
+++ b/opendj-server-legacy/src/test/java/org/opends/server/backends/jdbc/CachedConnectionTestCase.java
@@ -0,0 +1,1870 @@
+/*
+ * The contents of this file are subject to the terms of the Common Development and
+ * Distribution License (the License). You may not use this file except in compliance with the
+ * License.
+ *
+ * You can obtain a copy of the License at legal/CDDLv1.0.txt. See the License for the
+ * specific language governing permission and limitations under the License.
+ *
+ * When distributing Covered Software, include this CDDL Header Notice in each file and include
+ * the License file at legal/CDDLv1.0.txt. If applicable, add the following below the CDDL
+ * Header, with the fields enclosed by brackets [] replaced by your own identifying
+ * information: "Portions Copyright [year] [name of copyright owner]".
+ *
+ * Copyright 2026 3A Systems, LLC.
+ */
+package org.opends.server.backends.jdbc;
+
+import org.opends.server.DirectoryServerTestCase;
+import org.testng.annotations.AfterClass;
+import org.testng.annotations.AfterMethod;
+import org.testng.annotations.BeforeClass;
+import org.testng.annotations.BeforeMethod;
+import org.testng.annotations.DataProvider;
+import org.testng.annotations.Test;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.lang.reflect.Field;
+import java.net.InetAddress;
+import java.net.ServerSocket;
+import java.sql.Connection;
+import java.sql.Driver;
+import java.sql.DriverManager;
+import java.sql.DriverPropertyInfo;
+import java.sql.SQLException;
+import java.sql.SQLTimeoutException;
+import java.util.ArrayDeque;
+import java.util.Collections;
+import java.util.Deque;
+import java.util.IdentityHashMap;
+import java.util.Properties;
+import java.util.Set;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Executor;
+import java.util.concurrent.FutureTask;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.logging.Logger;
+
+import org.mockito.InOrder;
+
+import static org.mockito.Mockito.any;
+import static org.mockito.Mockito.anyInt;
+import static org.mockito.Mockito.doThrow;
+import static org.mockito.Mockito.eq;
+import static org.mockito.Mockito.inOrder;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+import static org.testng.Assert.assertEquals;
+import static org.testng.Assert.assertFalse;
+import static org.testng.Assert.assertNotNull;
+import static org.testng.Assert.assertNotSame;
+import static org.testng.Assert.assertNull;
+import static org.testng.Assert.assertSame;
+import static org.testng.Assert.assertTrue;
+import static org.testng.Assert.fail;
+
+/**
+ * The pool every operation of the JDBC backend borrows from must bound both of its phases and
+ * report a connect it cannot make, rather than retrying it out of sight of the caller (#872).
+ * Needs no database: the dialects are exercised against a socket that never answers and against a
+ * driver of this test, so a regression fails the build wherever it runs.
+ */
+@SuppressWarnings("javadoc")
+@Test(groups = { "precommit", "jdbc" }, sequential = true)
+public class CachedConnectionTestCase extends DirectoryServerTestCase {
+
+	/** A connect attempt of a bounded dialect must give up in about this long, plus room for a slow machine. */
+	private static final long BOUND_SECONDS = 2;
+	/**
+	 * Room for a slow machine on top of a bound, and no more than that. A minute of it turned
+	 * every assertion below into "it does not run forever": a connect that has to be reported at
+	 * once and a borrow that has to give up at its two second deadline both passed at 59 s.
+	 */
+	private static final long BOUND_MARGIN_MS = 10000;
+
+	private final StubDriver stub = new StubDriver();
+
+	/** The window as this JVM was started with it, put back after every test that varies it. */
+	private static final long CONFIGURED_ALIVE_BYPASS_NANOS = CachedConnection.aliveBypassNanos;
+
+	@BeforeClass
+	public void registerStubDriver() throws Exception {
+		DriverManager.registerDriver(stub);
+	}
+
+	@AfterClass
+	public void deregisterStubDriver() throws Exception {
+		DriverManager.deregisterDriver(stub);
+	}
+
+	/**
+	 * Most of the tests below seed the pool by hand, and a connection built a moment ago is inside
+	 * the alive window - they are about what the validation of a borrow does, so the window is off
+	 * unless the test at hand is one of the window's own.
+	 */
+	@BeforeMethod
+	public void validateEveryBorrow() {
+		CachedConnection.aliveBypassNanos = 0;
+	}
+
+	@AfterMethod
+	public void clearProperties() {
+		System.clearProperty(CachedConnection.CONNECT_TIMEOUT_PROPERTY);
+		System.clearProperty(CachedConnection.POOL_TIMEOUT_PROPERTY);
+		System.clearProperty(CachedConnection.TTL_PROPERTY);
+		System.clearProperty(CachedConnection.ALIVE_BYPASS_PROPERTY);
+		// what has been reported once is remembered for the life of the jvm: left standing, the key
+		// of one test is what the next one finds when it asserts that it reported something itself
+		CachedConnection.warnedOnce.clear();
+		CachedConnection.aliveBypassNanos = CONFIGURED_ALIVE_BYPASS_NANOS;
+	}
+
+	/**
+	 * A driver that is not on the classpath - the JDBC backend needs one dropped into
+	 * lib/extensions by hand - is a configuration error the caller has to see. Retried, it is
+	 * indistinguishable from a database that hangs.
+	 */
+	@Test(timeOut = 120000)
+	public void testMissingDriverIsReportedAtOnce() throws Exception {
+		final long startedAt = System.currentTimeMillis();
+		try {
+			CachedConnection.getConnection("jdbc:nosuchengine://127.0.0.1:5432/opendj");
+			fail("a connection string no registered driver accepts must be reported");
+		} catch (SQLException expected) {
+			assertTrue(expected.getMessage().contains("No suitable driver"), expected.getMessage());
+		}
+		assertElapsedWithinBound(startedAt, 0);
+	}
+
+	/**
+	 * ... and the report of it carries no password. This is the path the credentials leave by: the
+	 * jdk itself builds "No suitable driver found for " + url, a missing driver jar is the ordinary
+	 * oracle misconfiguration, and what this class throws reaches the server error log in full -
+	 * JDBCStorage.open() hands it to RootContainer, which makes the message of the cause the
+	 * message of what it throws, and BackendConfigManager logs that at ERROR and answers a config
+	 * change with it. Every link of the chain is asserted, not only the message on top: everything
+	 * that prints a failure prints its causes along with it.
+	 */
+	@Test(timeOut = 120000)
+	public void testAReportedConnectCarriesNoCredentials() throws Exception {
+		final String url = "jdbc:nosuchengine://opendj:S3cretOfTheBackend@127.0.0.1:5432/opendj";
+		try {
+			CachedConnection.getConnection(url);
+			fail("a connection string no registered driver accepts must be reported");
+		} catch (SQLException expected) {
+			assertNoCredentials(expected);
+			assertTrue(expected.getMessage().contains("No suitable driver"),
+				"the failure has to stay recognizable: " + expected.getMessage());
+			assertTrue(expected.getMessage().contains("127.0.0.1:5432"),
+				"the host is what a report of a connect is read for: " + expected.getMessage());
+		}
+	}
+
+	/**
+	 * A url this class knows no timeout properties for is reported once. The properties bounding a
+	 * connect are the ones of a driver, so a driver outside the four - an admin-added mariadb, an
+	 * h2 - leaves every attempt unbounded, and the deadline of the borrow cannot reach into a
+	 * connect already under way: the driver is the only thing holding the socket. Silently, that
+	 * is #872 again, for a backend nobody thinks of as unbounded.
+	 */
+	@Test(timeOut = 120000)
+	public void testAUrlThisBackendCannotBoundIsReportedOnce() throws Exception {
+		final String url = "jdbc:nosuchengine-unbounded://127.0.0.1:5432/opendj";
+		final String key = CachedConnection.safeUrl(url) + "|unknown-dialect";
+		// the set is the gate warnOnce() logs behind, so it has to start empty for this to be a
+		// test of what this borrow reported rather than of what some earlier one left behind
+		CachedConnection.warnedOnce.clear();
+		borrowExpectingFailure(url);
+		assertEquals(CachedConnection.warnedOnce, Collections.singleton(key),
+			"a connection string no bound of this class can reach was not reported");
+
+		// ... and once: every operation of the backend borrows through here, so a report per borrow
+		// is one nobody reads. A second borrow that would log again is one that adds a key again.
+		CachedConnection.warnedOnce.remove(key);
+		borrowExpectingFailure(url);
+		assertEquals(CachedConnection.warnedOnce, Collections.singleton(key),
+			"the report is not the one warnOnce() gates: " + CachedConnection.warnedOnce);
+		borrowExpectingFailure(url);
+		assertEquals(CachedConnection.warnedOnce, Collections.singleton(key),
+			"the same url was reported a second time");
+	}
+
+	/** A borrow that has to fail: what the test is after is what was logged on the way. */
+	private static void borrowExpectingFailure(String url) throws Exception {
+		try {
+			CachedConnection.getConnection(url);
+			fail("a connection string no registered driver accepts must be reported");
+		} catch (SQLException expected) {
+			// the point of the test is what was logged on the way, not what came back
+		}
+	}
+
+	/**
+	 * ... and so is a postgresql url that turns the read bound off: a parameter of one outranks the
+	 * property this class supplies, so a "socketTimeout=0" there cannot be replaced. Nothing is
+	 * left to end a borrow that reaches a database accepting the connection and answering nothing,
+	 * and an administrator who wrote that zero has to be able to find it in the log.
+	 */
+	@Test
+	public void testAReadBoundTurnedOffInAPostgresUrlIsReportedOnce() throws Exception {
+		final String url = "jdbc:postgresql://reported:5432/db?socketTimeout=0";
+		final String key = CachedConnection.safeUrl(url) + "|unbounded|socketTimeout";
+		CachedConnection.warnedOnce.clear();
+		assertFalse(CachedConnection.ConnectDialect.POSTGRES.bound(url, new Properties(), 7));
+		assertEquals(CachedConnection.warnedOnce, Collections.singleton(key),
+			"a url leaving the reads of its login unbounded was not reported");
+
+		assertFalse(CachedConnection.ConnectDialect.POSTGRES.bound(url, new Properties(), 7));
+		assertEquals(CachedConnection.warnedOnce, Collections.singleton(key),
+			"the same url was reported a second time");
+	}
+
+	/**
+	 * ... and every parameter of it that is turned off, not only the first one. A url is free to
+	 * turn off the read bound and the login bound both, and the login bound is the per-host budget
+	 * of a failover url - safeUrl() keeps neither parameter, so a key of the url alone would name
+	 * the first offender, remember the url as reported, and leave the rest of them unmentionable.
+	 */
+	@Test
+	public void testEveryBoundTurnedOffInAPostgresUrlIsReported() throws Exception {
+		final String url = "jdbc:postgresql://reported-twice:5432/db?socketTimeout=0&loginTimeout=0";
+		final String safe = CachedConnection.safeUrl(url);
+		CachedConnection.warnedOnce.clear();
+
+		CachedConnection.ConnectDialect.POSTGRES.bound(url, new Properties(), 7);
+
+		assertTrue(CachedConnection.warnedOnce.contains(safe + "|unbounded|socketTimeout"),
+			"the read bound left at 0 was not reported: " + CachedConnection.warnedOnce);
+		assertTrue(CachedConnection.warnedOnce.contains(safe + "|unbounded|loginTimeout"),
+			"the login bound left at 0 was not reported: " + CachedConnection.warnedOnce);
+	}
+
+	/**
+	 * Nothing in the chain of a failure names the password of the backend, however deep it stands.
+	 * Walked by identity rather than link by link: a driver is free to make the cause and the next
+	 * exception of a link the same failure, which is the very shape the sibling test builds, and a
+	 * helper looping on it would hang the run it is checking for exactly that.
+	 */
+	private static void assertNoCredentials(Throwable failure) {
+		final Set<Throwable> seen = Collections.newSetFromMap(new IdentityHashMap<Throwable, Boolean>());
+		final Deque<Throwable> pending = new ArrayDeque<>();
+		enqueue(pending, seen, failure);
+		while (!pending.isEmpty()) {
+			final Throwable t = pending.poll();
+			assertFalse(String.valueOf(t.getMessage()).contains("S3cretOfTheBackend"),
+				"the password of the backend reached a message: " + t);
+			if (t instanceof SQLException) {
+				enqueue(pending, seen, ((SQLException) t).getNextException());
+			}
+			enqueue(pending, seen, t.getCause());
+		}
+	}
+
+	private static void enqueue(Deque<Throwable> pending, Set<Throwable> seen, Throwable t) {
+		if (t != null && seen.add(t)) {
+			pending.add(t);
+		}
+	}
+
+	/**
+	 * A link of a chain carries a cause and a next exception both, and a driver is free to make the
+	 * two the same failure. Rebuilt under a bound on the depth alone, a chain of those is copied
+	 * twice over at every step - 2^32 links for one reaching the bound, which is a report of a
+	 * failed connect that never comes back. What bounds the redaction is the number of links it
+	 * rebuilds, the way the walk looking for credentials is bounded by the ones it visits.
+	 */
+	@Test(timeOut = 60000)
+	public void testAFailureWhoseCauseIsItsNextExceptionIsRedactedInBoundedTime() throws Exception {
+		final String url = "jdbc:postgresql://opendj:S3cretOfTheBackend@127.0.0.1:5432/opendj";
+		SQLException chain = new SQLException("connect to " + url + " failed", "08006", 1);
+		for (int i = 0; i < 64; i++) {
+			final SQLException link = new SQLException("link " + i + " of " + url, "08006", i);
+			link.setNextException(chain);
+			link.initCause(chain);
+			chain = link;
+		}
+		final SQLException reported = CachedConnection.reported(chain, url);
+		assertNoCredentials(reported);
+		assertEquals(reported.getSQLState(), "08006", "the SQLState of a link has to survive its redaction");
+	}
+
+	/**
+	 * ... and the chain of one is walked link by link rather than copy by copy. Enqueued twice, a
+	 * failure whose cause is its own next exception fans out into a level twice the size of the one
+	 * above it, so five levels of it are enough to spend the whole budget of the walk: the link
+	 * that names the url stands at level six of seven and was never reached - and a walk that ends
+	 * without finding credentials is one that reports the failure as it stands, password and all.
+	 */
+	@Test(timeOut = 60000)
+	public void testACredentialBehindADuplicatedChainIsStillRedacted() throws Exception {
+		final String url = "jdbc:postgresql://opendj:S3cretOfTheBackend@127.0.0.1:5432/opendj";
+		SQLException chain = new SQLException("connect to " + url + " failed", "08006", 1);
+		for (int i = 0; i < 6; i++) {
+			final SQLException link = new SQLException("wrapper " + i, "08006", i);
+			link.setNextException(chain);
+			link.initCause(chain);
+			chain = link;
+		}
+
+		assertNoCredentials(CachedConnection.reported(chain, url));
+	}
+
+	/**
+	 * The tail a rebuild has no budget left for is named rather than dropped. Without it the same
+	 * failure keeps its root cause where the url of the backend carries no password and loses it
+	 * without a word where it does - and the root cause is what a report of a failed connect is
+	 * read for.
+	 */
+	@Test(timeOut = 60000)
+	public void testTheTailOfALongChainIsNamedRatherThanDropped() throws Exception {
+		final String url = "jdbc:postgresql://opendj:S3cretOfTheBackend@127.0.0.1:5432/opendj";
+		SQLException chain = new SQLException("Connection to 127.0.0.1:5432 refused", "08006", 1);
+		for (int i = 0; i < 40; i++) {
+			final SQLException link = new SQLException("wrapper " + i + " of " + url, "08006", i);
+			link.initCause(chain);
+			chain = link;
+		}
+
+		final SQLException reported = CachedConnection.reported(chain, url);
+
+		assertNoCredentials(reported);
+		Throwable last = reported;
+		while (last.getCause() != null) {
+			last = last.getCause();
+		}
+		assertTrue(String.valueOf(last.getMessage()).contains("left out"),
+			"the tail a rebuild had no budget for has to say so: " + last.getMessage());
+	}
+
+	/**
+	 * A database that is not listening at all: every dialect reports it instead of retrying the
+	 * refused connect until the caller gives up on the operation.
+	 */
+	@Test(timeOut = 120000)
+	public void testRefusedConnectIsReportedAtOnce() throws Exception {
+		final int closedPort = closedPort();
+		System.setProperty(CachedConnection.CONNECT_TIMEOUT_PROPERTY, Long.toString(BOUND_SECONDS));
+		for (final String url : urlsOf(closedPort)) {
+			final long startedAt = System.currentTimeMillis();
+			try {
+				CachedConnection.getConnection(url);
+				fail("a refused connect must be reported: " + CachedConnection.safeUrl(url));
+			} catch (SQLException expected) {
+				// the failure of the moment, reported rather than retried
+			}
+			assertElapsedWithinBound(startedAt, BOUND_SECONDS * 1000);
+		}
+	}
+
+	/**
+	 * The failure this bound exists for: a database that completes the TCP connection and then
+	 * says nothing - a moved VIP, a proxy at its connection limit, a host that lost its answer -
+	 * leaving the login of the driver, and with it the operation, without an end. The connection
+	 * of the accept queue is never answered here, so every dialect has to give up on its own.
+	 */
+	@Test(timeOut = 300000)
+	public void testLoginIsBoundedWhenTheDatabaseNeverAnswers() throws Exception {
+		System.setProperty(CachedConnection.CONNECT_TIMEOUT_PROPERTY, Long.toString(BOUND_SECONDS));
+		// a socket that is bound and never accepted: the kernel completes the handshake, so the
+		// connect of the driver succeeds and every read of the login that follows hangs
+		try (final ServerSocket blackhole = new ServerSocket(0, 50, InetAddress.getLoopbackAddress())) {
+			for (final String url : urlsOf(blackhole.getLocalPort())) {
+				// borrowed on a thread of its own: a bound that a driver does not honour has to
+				// fail this test at once, and not by hanging the run it is part of
+				final FutureTask<Connection> borrow = new FutureTask<>(() -> CachedConnection.getConnection(url));
+				final Thread thread = new Thread(borrow, "borrow-" + CachedConnection.safeUrl(url));
+				thread.setDaemon(true);
+				thread.start();
+				try {
+					final Connection con = borrow.get(BOUND_SECONDS * 1000 + BOUND_MARGIN_MS, TimeUnit.MILLISECONDS);
+					fail("a database that never answers must not hand out a connection: " + con);
+				} catch (TimeoutException e) {
+					fail("the login of " + CachedConnection.safeUrl(url) + " is not bounded: it never gave up");
+				} catch (ExecutionException expected) {
+					assertTrue(expected.getCause() instanceof SQLException, String.valueOf(expected.getCause()));
+				}
+			}
+		}
+	}
+
+	/**
+	 * The deadline of the borrow bounds the attempt inside it as well: the pool timeout stands for
+	 * the whole borrow, and an attempt left to run out its own bound would overrun it by that bound.
+	 */
+	@Test(timeOut = 120000)
+	public void testTheAttemptIsBoundedByTheDeadlineOfTheBorrow() throws Exception {
+		System.setProperty(CachedConnection.CONNECT_TIMEOUT_PROPERTY, "600");
+		System.setProperty(CachedConnection.POOL_TIMEOUT_PROPERTY, "2");
+		try (final ServerSocket blackhole = new ServerSocket(0, 50, InetAddress.getLoopbackAddress())) {
+			final String url = "jdbc:postgresql://127.0.0.1:" + blackhole.getLocalPort() + "/opendj?user=opendj&password=opendj";
+			final long startedAt = System.currentTimeMillis();
+			try {
+				CachedConnection.getConnection(url);
+				fail("a database that never answers must not hand out a connection");
+			} catch (SQLException expected) {
+				// reported, and within the borrow it was given rather than the 600 s of the attempt
+			}
+			final long elapsed = System.currentTimeMillis() - startedAt;
+			assertTrue(elapsed < 2000 + BOUND_MARGIN_MS,
+				"the attempt outlived the deadline of the borrow: " + elapsed + " ms");
+		}
+	}
+
+	/** Pool exhaustion stays a retry - one of our own connections is on its way back to the pool. */
+	@Test(timeOut = 120000)
+	public void testConnectionLimitIsRetried() throws Exception {
+		final String url = StubDriver.PREFIX + "retried";
+		stub.failWith(tooManyConnections(), 2);
+		System.setProperty(CachedConnection.POOL_TIMEOUT_PROPERTY, "30");
+
+		final Connection con = CachedConnection.getConnection(url);
+
+		assertNotNull(con);
+		assertEquals(stub.attempts.get(), 3, "the connect must be retried while the database is at its limit");
+	}
+
+	/** ... but under a deadline: the retry used to double its wait from 1 ms with no end to it. */
+	@Test(timeOut = 120000)
+	public void testConnectionLimitGivesUpAtTheDeadline() throws Exception {
+		final String url = StubDriver.PREFIX + "deadline";
+		stub.failWith(tooManyConnections(), StubDriver.ALWAYS);
+		System.setProperty(CachedConnection.POOL_TIMEOUT_PROPERTY, "2");
+
+		final long startedAt = System.currentTimeMillis();
+		try {
+			CachedConnection.getConnection(url);
+			fail("a database that stays at its connection limit must be reported, not waited out forever");
+		} catch (SQLTimeoutException expected) {
+			assertTrue(expected.getMessage().contains("2s"), expected.getMessage());
+			assertEquals(((SQLException) expected.getCause()).getSQLState(), "53300");
+			// the state of a connect that did not happen, rather than none at all: this is the
+			// failure of a borrow, and monitoring reading the state off what it caught would
+			// otherwise see null where the driver's own exception carried one
+			assertEquals(expected.getSQLState(), "08001");
+		}
+		final long elapsed = System.currentTimeMillis() - startedAt;
+		assertTrue(elapsed >= 2000, "gave up after " + elapsed + " ms, before the deadline it was given");
+		assertElapsedWithinBound(startedAt, 2000);
+		assertTrue(stub.attempts.get() > 1, "the connect must be retried while the deadline lasts");
+	}
+
+	/**
+	 * A database on its way up - starting, recovering, shutting down - says so, and says it for
+	 * seconds: the backend it belongs to would otherwise stay locked down until the next restart
+	 * of the server, since nothing above JDBCStorage.open() attempts it a second time.
+	 */
+	@Test(timeOut = 120000)
+	public void testDatabaseOnItsWayUpIsRetried() throws Exception {
+		final String url = StubDriver.PREFIX + "starting-up";
+		stub.failWith(new SQLException("the database system is starting up", "57P03"), 2);
+		System.setProperty(CachedConnection.POOL_TIMEOUT_PROPERTY, "30");
+
+		final Connection con = CachedConnection.getConnection(url);
+
+		assertNotNull(con);
+		assertEquals(stub.attempts.get(), 3, "a database that is starting up must be waited out");
+	}
+
+	/** ... and it is recognized however the driver wrapped it: a SQLException carries two chains. */
+	@Test(timeOut = 120000)
+	public void testTheWholeChainOfTheFailureIsLookedAt() throws Exception {
+		final String url = StubDriver.PREFIX + "wrapped";
+		final SQLException wrapped = new SQLException("could not connect to the server", "08006");
+		wrapped.setNextException(tooManyConnections());
+		stub.failWith(wrapped, 1);
+		System.setProperty(CachedConnection.POOL_TIMEOUT_PROPERTY, "30");
+
+		assertNotNull(CachedConnection.getConnection(url));
+		assertEquals(stub.attempts.get(), 2, "the failure behind the one reported must be looked at");
+	}
+
+	/**
+	 * The rest of the insufficient_resources class is not worth waiting out: a server out of disk
+	 * is not made whole by a connection of ours coming back to the pool.
+	 */
+	@Test(timeOut = 120000)
+	public void testDiskFullIsNotRetried() throws Exception {
+		final String url = StubDriver.PREFIX + "disk-full";
+		stub.failWith(new SQLException("could not extend file: No space left on device", "53100"), StubDriver.ALWAYS);
+		System.setProperty(CachedConnection.POOL_TIMEOUT_PROPERTY, "30");
+
+		try {
+			CachedConnection.getConnection(url);
+			fail("a database out of disk must be reported to the caller");
+		} catch (SQLException expected) {
+			assertEquals(expected.getSQLState(), "53100");
+		}
+		assertEquals(stub.attempts.get(), 1, "a failure that waiting cannot clear must be attempted once");
+	}
+
+	/**
+	 * Every other failure is the caller's to report. A password the database does not accept is
+	 * never going to be accepted by waiting, and the retry that swallowed it left the operation
+	 * hanging with nothing in the log.
+	 */
+	@Test(timeOut = 120000)
+	public void testRejectedLoginIsNotRetried() throws Exception {
+		final String url = StubDriver.PREFIX + "rejected";
+		stub.failWith(new SQLException("password authentication failed", "28P01"), StubDriver.ALWAYS);
+		System.setProperty(CachedConnection.POOL_TIMEOUT_PROPERTY, "30");
+
+		try {
+			CachedConnection.getConnection(url);
+			fail("a rejected login must be reported to the caller");
+		} catch (SQLException expected) {
+			assertEquals(expected.getSQLState(), "28P01");
+		}
+		assertEquals(stub.attempts.get(), 1, "a rejected login must be attempted once");
+	}
+
+	/** A connection the setup of which failed belongs to nobody: it has to be closed, not leaked. */
+	@Test(timeOut = 120000)
+	public void testConnectionIsClosedWhenItsSetupFails() throws Exception {
+		final String url = StubDriver.PREFIX + "setup-failure";
+		final Connection broken = mock(Connection.class);
+		doThrow(new SQLException("read only")).when(broken).setAutoCommit(false);
+		stub.answerWith(broken);
+
+		try {
+			CachedConnection.getConnection(url);
+			fail("a connection that cannot be set up must be reported");
+		} catch (SQLException expected) {
+			assertEquals(expected.getMessage(), "read only");
+		}
+		verify(broken).close();
+	}
+
+	/** The same, for a driver whose failure in the setup is not a SQLException but an unchecked one. */
+	@Test(timeOut = 120000)
+	public void testConnectionIsClosedWhenItsSetupFailsWithAnUncheckedError() throws Exception {
+		final String url = StubDriver.PREFIX + "setup-unchecked";
+		final Connection broken = mock(Connection.class);
+		doThrow(new IllegalStateException("driver internal")).when(broken).setTransactionIsolation(anyInt());
+		stub.answerWith(broken);
+
+		try {
+			CachedConnection.getConnection(url);
+			fail("a connection that cannot be set up must be reported");
+		} catch (IllegalStateException expected) {
+			assertEquals(expected.getMessage(), "driver internal");
+		}
+		verify(broken).close();
+	}
+
+	/**
+	 * isValid(n) is not a bound at the socket on every driver - the SQL Server driver turns it
+	 * into a query timeout, which needs an answer from the server to fire - and the read bound of
+	 * the login was lifted the moment the connection was established, so the socket carries the
+	 * bound of the validation, for the length of the validation only.
+	 */
+	@Test(timeOut = 120000)
+	public void testValidationOfAPooledConnectionIsBoundedAtTheSocket() throws Exception {
+		final String url = StubDriver.PREFIX + "validation-bound";
+		final Connection pooled = mock(Connection.class);
+		when(pooled.isValid(anyInt())).thenReturn(true);
+		when(pooled.getNetworkTimeout()).thenReturn(0);
+		seedPool(url, pooled);
+
+		final Connection borrowed = CachedConnection.getConnection(url);
+
+		assertSame(((CachedConnection) borrowed).parent, pooled);
+		final InOrder inOrder = inOrder(pooled);
+		inOrder.verify(pooled).setNetworkTimeout(any(Executor.class), eq(CachedConnection.VALIDATION_TIMEOUT_SECONDS * 1000));
+		inOrder.verify(pooled).isValid(CachedConnection.VALIDATION_TIMEOUT_SECONDS);
+		inOrder.verify(pooled).setNetworkTimeout(any(Executor.class), eq(0));
+	}
+
+	/**
+	 * A driver that takes the call bounding the validation and then fails inside it is told apart
+	 * from one that never takes a network timeout at all: it is free to have applied the bound
+	 * before failing, so the connection is discarded rather than validated unbounded and handed
+	 * out - pooled, it would carry five seconds of ours into every statement for the rest of its
+	 * life, and the import batch of a backend open is the first thing to die of that.
+	 */
+	@Test(timeOut = 120000)
+	public void testAPooledConnectionThatCannotBeBoundedForItsValidationIsDiscarded() throws Exception {
+		final String url = StubDriver.PREFIX + "validation-bound-fails";
+		final Connection pooled = mock(Connection.class);
+		when(pooled.getNetworkTimeout()).thenReturn(0);
+		when(pooled.isValid(anyInt())).thenReturn(true);
+		doThrow(new SQLException("the driver took the bound and then failed"))
+			.when(pooled).setNetworkTimeout(any(Executor.class), anyInt());
+		seedPool(url, pooled);
+		final Connection fresh = mock(Connection.class);
+		stub.answerWith(fresh);
+
+		final Connection borrowed = CachedConnection.getConnection(url);
+
+		assertSame(((CachedConnection) borrowed).parent, fresh, "a connection this could not bound was handed out");
+		verify(pooled, never()).isValid(anyInt());
+		verify(pooled).close();
+	}
+
+	/**
+	 * A driver answering a negative network timeout is outside the contract of the call - 0 is no
+	 * limit and nothing below it stands for anything - and taken back as it is, it is one of the
+	 * two sentinels this class tells its own outcomes apart by: the bound of the validation would
+	 * be read as a bound that was never set, and the connection would go back into the pool still
+	 * carrying five seconds of ours into every statement of the next borrower.
+	 */
+	@Test(timeOut = 120000)
+	public void testAPooledConnectionWhoseDriverAnswersANegativeBoundIsPutBackUnbounded() throws Exception {
+		final String url = StubDriver.PREFIX + "validation-negative-bound";
+		final Connection pooled = mock(Connection.class);
+		when(pooled.isValid(anyInt())).thenReturn(true);
+		when(pooled.getNetworkTimeout()).thenReturn(-1);
+		CachedConnection.cached.get(url).add(new CachedConnection(url, pooled));
+
+		final Connection borrowed = CachedConnection.getConnection(url);
+
+		assertSame(((CachedConnection) borrowed).parent, pooled);
+		final InOrder inOrder = inOrder(pooled);
+		inOrder.verify(pooled)
+			.setNetworkTimeout(any(Executor.class), eq(CachedConnection.VALIDATION_TIMEOUT_SECONDS * 1000));
+		inOrder.verify(pooled).isValid(CachedConnection.VALIDATION_TIMEOUT_SECONDS);
+		inOrder.verify(pooled).setNetworkTimeout(any(Executor.class), eq(0));
+	}
+
+	/** A read bound of the connection string is tighter than ours and stays untouched. */
+	@Test(timeOut = 120000)
+	public void testValidationLeavesTheBoundOfTheConnectionStringAlone() throws Exception {
+		final String url = StubDriver.PREFIX + "validation-tighter";
+		final Connection pooled = mock(Connection.class);
+		when(pooled.isValid(anyInt())).thenReturn(true);
+		when(pooled.getNetworkTimeout()).thenReturn(2000);
+		seedPool(url, pooled);
+
+		assertNotNull(CachedConnection.getConnection(url));
+
+		verify(pooled, never()).setNetworkTimeout(any(Executor.class), anyInt());
+	}
+
+	/**
+	 * The pool has no upper bound on the number of connections it holds, and a validation is a
+	 * round trip: after a failover that left them half-open, draining the pool must not outlive
+	 * the deadline of the borrow - establishing a connection is the faster answer past it.
+	 */
+	@Test(timeOut = 120000)
+	public void testDrainOfThePoolStopsAtTheDeadline() throws Exception {
+		final String url = StubDriver.PREFIX + "drain-deadline";
+		final int pooled = 8;
+		final AtomicInteger validated = new AtomicInteger();
+		for (int i = 0; i < pooled; i++) {
+			final Connection stale = mock(Connection.class);
+			when(stale.isValid(anyInt())).thenAnswer(invocation -> {
+				validated.incrementAndGet();
+				Thread.sleep(500); // a database that no longer answers: every validation waits out its bound
+				return false;
+			});
+			seedPool(url, stale);
+		}
+		final Connection fresh = mock(Connection.class);
+		stub.answerWith(fresh);
+		System.setProperty(CachedConnection.POOL_TIMEOUT_PROPERTY, "1");
+
+		final Connection borrowed = CachedConnection.getConnection(url);
+
+		assertSame(((CachedConnection) borrowed).parent, fresh);
+		assertTrue(validated.get() > 0 && validated.get() < pooled,
+			"the drain has to start and to stop at the deadline: " + validated.get() + " of " + pooled);
+	}
+
+	/** A pooled connection that no longer validates is closed and replaced, not handed out. */
+	@Test(timeOut = 120000)
+	public void testBrokenPooledConnectionIsDiscarded() throws Exception {
+		final String url = StubDriver.PREFIX + "broken-pooled";
+		final Connection stale = mock(Connection.class);
+		when(stale.isValid(anyInt())).thenReturn(false);
+		seedPool(url, stale);
+		final Connection fresh = mock(Connection.class);
+		when(fresh.isValid(anyInt())).thenReturn(true);
+		stub.answerWith(fresh);
+
+		final Connection borrowed = CachedConnection.getConnection(url);
+
+		assertSame(((CachedConnection) borrowed).parent, fresh);
+		verify(stale).close();
+		// the validation of a pooled connection needs a bound of its own as well
+		verify(stale, never()).isValid(0);
+		verify(stale).isValid(CachedConnection.VALIDATION_TIMEOUT_SECONDS);
+	}
+
+	/**
+	 * The same for a driver whose answer to the validation is an unchecked failure: it unwinds
+	 * through poll(), which stands outside every try of the borrow, so the connection it was
+	 * raised over is already out of the pool and would be held by nobody.
+	 */
+	@Test(timeOut = 120000)
+	public void testAPooledConnectionWhoseValidationThrowsIsDiscarded() throws Exception {
+		final String url = StubDriver.PREFIX + "validation-unchecked";
+		final Connection broken = mock(Connection.class);
+		when(broken.isValid(anyInt())).thenThrow(new IllegalStateException("driver internal"));
+		seedPool(url, broken);
+		final Connection fresh = mock(Connection.class);
+		stub.answerWith(fresh);
+
+		final Connection borrowed = CachedConnection.getConnection(url);
+
+		assertSame(((CachedConnection) borrowed).parent, fresh);
+		verify(broken).close();
+	}
+
+	/** A connection that cannot be rolled back must not go back into the pool - nor be dropped. */
+	@Test(timeOut = 120000)
+	public void testConnectionThatCannotBeRolledBackIsClosed() throws Exception {
+		final String url = StubDriver.PREFIX + "rollback-failure";
+		final Connection parent = mock(Connection.class);
+		doThrow(new SQLException("connection is closed")).when(parent).rollback();
+
+		try {
+			new CachedConnection(url, parent).close();
+			fail("a failed rollback must be reported");
+		} catch (SQLException expected) {
+			assertEquals(expected.getMessage(), "connection is closed");
+		}
+		verify(parent).close();
+		assertTrue(CachedConnection.cached.get(url).isEmpty(), "a connection that cannot be rolled back was pooled");
+	}
+
+	@Test
+	public void testDialectIsRecognizedByTheConnectionString() throws Exception {
+		assertEquals(CachedConnection.ConnectDialect.of("jdbc:postgresql://h:5432/db"), CachedConnection.ConnectDialect.POSTGRES);
+		assertEquals(CachedConnection.ConnectDialect.of("jdbc:mysql://h:3306/db"), CachedConnection.ConnectDialect.MYSQL);
+		assertEquals(CachedConnection.ConnectDialect.of("jdbc:oracle:thin:@//h:1521/svc"), CachedConnection.ConnectDialect.ORACLE);
+		assertEquals(CachedConnection.ConnectDialect.of("jdbc:sqlserver://h:1433;databaseName=db"), CachedConnection.ConnectDialect.MICROSOFT);
+		assertNull(CachedConnection.ConnectDialect.of("jdbc:h2:mem:db"), "an unknown engine must not be fed the properties of another");
+	}
+
+	/** Both phases are bounded, in the units of the driver: the connect alone leaves the login open. */
+	@Test
+	public void testBothPhasesOfTheLoginAreBounded() throws Exception {
+		// pgjdbc puts an SO_TIMEOUT on the login socket only where socketTimeout is set: without it
+		// loginTimeout bounds the caller alone, and the thread the driver runs the login on stays
+		// parked in the read it abandoned
+		final Properties postgres = new Properties();
+		assertTrue(CachedConnection.ConnectDialect.POSTGRES.bound("jdbc:postgresql://h:5432/db", postgres, 7),
+			"the read bound of postgresql outlives the login and has to be lifted");
+		assertEquals(postgres.getProperty("connectTimeout"), "7");
+		assertEquals(postgres.getProperty("socketTimeout"), "7");
+		assertEquals(postgres.getProperty("loginTimeout"), "7", "the bound of a url naming more than one host");
+
+		final Properties mysql = new Properties();
+		assertTrue(CachedConnection.ConnectDialect.MYSQL.bound("jdbc:mysql://h:3306/db", mysql, 7),
+			"the read bound of mysql outlives the login and has to be lifted");
+		assertEquals(mysql.getProperty("connectTimeout"), "7000");
+		assertEquals(mysql.getProperty("socketTimeout"), "7000");
+
+		final Properties oracle = new Properties();
+		assertTrue(CachedConnection.ConnectDialect.ORACLE.bound("jdbc:oracle:thin:@//h:1521/svc", oracle, 7));
+		assertEquals(oracle.getProperty("oracle.net.CONNECT_TIMEOUT"), "7000");
+		assertEquals(oracle.getProperty("oracle.jdbc.ReadTimeout"), "7000");
+
+		// the loginTimeout of the sql server driver leaves the read of the prelogin answer open
+		final Properties microsoft = new Properties();
+		assertTrue(CachedConnection.ConnectDialect.MICROSOFT.bound("jdbc:sqlserver://h:1433;databaseName=db", microsoft, 7));
+		assertEquals(microsoft.getProperty("loginTimeout"), "7");
+		assertEquals(microsoft.getProperty("socketTimeout"), "7000");
+	}
+
+	/**
+	 * A driver with a range of its own for its connect property is never handed a value beyond it:
+	 * SQLServerDriverIntProperty.LOGIN_TIMEOUT is validated against [0, 65535], so a bound past
+	 * that would not widen the connect, it would fail every one of them.
+	 */
+	@Test
+	public void testConnectBoundStaysInTheRangeTheDriverTakes() throws Exception {
+		final Properties microsoft = new Properties();
+		CachedConnection.ConnectDialect.MICROSOFT.bound("jdbc:sqlserver://h:1433;databaseName=db", microsoft, 100000);
+		assertEquals(microsoft.getProperty("loginTimeout"), "65535");
+		assertEquals(microsoft.getProperty("socketTimeout"), "100000000", "the read bound takes any value");
+	}
+
+	/**
+	 * A bound the administrator put into the connection string by hand - the only workaround this
+	 * backend had - keeps precedence, property by property.
+	 */
+	@Test
+	public void testConnectionStringKeepsPrecedence() throws Exception {
+		final Properties postgres = new Properties();
+		CachedConnection.ConnectDialect.POSTGRES.bound(
+			"jdbc:postgresql://h:5432/db?user=u&password=p&loginTimeout=30&socketTimeout=300", postgres, 7);
+		assertNull(postgres.getProperty("loginTimeout"), "the setting of the connection string was overridden");
+		assertNull(postgres.getProperty("socketTimeout"), "the setting of the connection string was overridden");
+		assertNull(postgres.getProperty("connectTimeout"),
+			"the connect side is one budget: a bound of the administrator under either of its names is theirs");
+
+		// the sql server driver gives a supplied property precedence over the one of the url
+		final Properties microsoft = new Properties();
+		CachedConnection.ConnectDialect.MICROSOFT.bound("jdbc:sqlserver://h:1433;loginTimeout=45;databaseName=db", microsoft, 7);
+		assertNull(microsoft.getProperty("loginTimeout"), "the setting of the connection string was overridden");
+		assertEquals(microsoft.getProperty("socketTimeout"), "7000");
+
+		// inside the descriptor of an oracle tns url the property goes by the last segment of its name
+		final Properties oracle = new Properties();
+		CachedConnection.ConnectDialect.ORACLE.bound(
+			"jdbc:oracle:thin:@(DESCRIPTION=(CONNECT_TIMEOUT=3)(ADDRESS=(HOST=h)(PORT=1521)))", oracle, 7);
+		assertNull(oracle.getProperty("oracle.net.CONNECT_TIMEOUT"));
+		assertEquals(oracle.getProperty("oracle.jdbc.ReadTimeout"), "7000");
+
+		// inside the descriptor the read bound goes by READ_TIMEOUT, and one of the administrator
+		// is never lifted after the login, because ours is not set on top of it
+		final Properties read = new Properties();
+		assertFalse(CachedConnection.ConnectDialect.ORACLE.bound(
+			"jdbc:oracle:thin:@(DESCRIPTION=(READ_TIMEOUT=30)(ADDRESS=(HOST=h)(PORT=1521)))", read, 7),
+			"a read bound of the connection string must not be lifted once the login is through");
+		assertNull(read.getProperty("oracle.jdbc.ReadTimeout"));
+
+		// ... while RECV_TIMEOUT is a parameter of sqlnet.ora and of the listener that ojdbc8 does
+		// not read - the name appears nowhere in the driver - so a descriptor carrying one is not
+		// a read bound of the connection and must not take ours off it
+		final Properties recv = new Properties();
+		assertTrue(CachedConnection.ConnectDialect.ORACLE.bound(
+			"jdbc:oracle:thin:@(DESCRIPTION=(RECV_TIMEOUT=30)(ADDRESS=(HOST=h)(PORT=1521)))", recv, 7),
+			"a parameter no driver reads left the login of this connection unbounded");
+		assertEquals(recv.getProperty("oracle.jdbc.ReadTimeout"), "7000");
+
+		// a name that only appears as the tail of another parameter is not a setting of its own
+		final Properties mysql = new Properties();
+		CachedConnection.ConnectDialect.MYSQL.bound("jdbc:mysql://h:3306/db?xconnectTimeout=1&socketTimeoutX=2", mysql, 7);
+		assertEquals(mysql.getProperty("connectTimeout"), "7000");
+		assertEquals(mysql.getProperty("socketTimeout"), "7000");
+	}
+
+	/**
+	 * A parameter is recognized the way the driver of its dialect recognizes it: pgjdbc and
+	 * Connector/J look their properties up by their exact name, so a name of another case is a
+	 * parameter of nobody - neither side bounds anything by it - and must not pass for a bound the
+	 * administrator set, while the other two match either way.
+	 */
+	@Test
+	public void testTheCaseOfAParameterIsTheOneOfItsDriver() throws Exception {
+		final Properties postgres = new Properties();
+		CachedConnection.ConnectDialect.POSTGRES.bound("jdbc:postgresql://h:5432/db?ConnectTimeout=5", postgres, 7);
+		assertEquals(postgres.getProperty("connectTimeout"), "7", "pgjdbc ignores a parameter of another case");
+
+		// PropertyKey.fromValue("SocketTimeout") answers null, and Connector/J then reads no bound
+		// out of the url either: a mis-cased parameter left the borrower parked on a host that
+		// completes the handshake and says nothing
+		final Properties mysql = new Properties();
+		CachedConnection.ConnectDialect.MYSQL.bound("jdbc:mysql://h:3306/db?SocketTimeout=1", mysql, 7);
+		assertEquals(mysql.getProperty("socketTimeout"), "7000", "Connector/J ignores a parameter of another case");
+
+		final Properties microsoft = new Properties();
+		CachedConnection.ConnectDialect.MICROSOFT.bound("jdbc:sqlserver://h:1433;LoginTimeout=45", microsoft, 7);
+		assertNull(microsoft.getProperty("loginTimeout"), "the sql server driver normalizes the name of a property");
+
+		// the keywords of an oracle descriptor are matched without regard to case as well
+		final Properties oracle = new Properties();
+		CachedConnection.ConnectDialect.ORACLE.bound(
+			"jdbc:oracle:thin:@(description=(connect_timeout=3)(address=(host=h)(port=1521)))", oracle, 7);
+		assertNull(oracle.getProperty("oracle.net.CONNECT_TIMEOUT"), "an oracle descriptor is read without case");
+	}
+
+	/**
+	 * The connection string is not the only channel of the administrator: the oracle driver reads
+	 * some of its properties out of the system properties as well, which is how a whole jvm is
+	 * bounded with -Doracle.jdbc.ReadTimeout. A property supplied to the driver outranks that one
+	 * without a word, and this class would then lift it once the login is through as if it were
+	 * its own - leaving a connection with no read bound at all where the administrator set one.
+	 */
+	@Test
+	public void testASystemPropertyOfTheAdministratorKeepsPrecedence() throws Exception {
+		System.setProperty("oracle.jdbc.ReadTimeout", "30000");
+		try {
+			final Properties oracle = new Properties();
+			assertFalse(CachedConnection.ConnectDialect.ORACLE.bound("jdbc:oracle:thin:@//h:1521/svc", oracle, 7),
+				"a read bound of the administrator must not be lifted once the login is through");
+			assertNull(oracle.getProperty("oracle.jdbc.ReadTimeout"), "the setting of the administrator was overridden");
+			assertEquals(oracle.getProperty("oracle.net.CONNECT_TIMEOUT"), "7000",
+				"the property it leaves open must still be bounded");
+		} finally {
+			System.clearProperty("oracle.jdbc.ReadTimeout");
+		}
+
+		// the connect property of the same driver, over the same channel
+		System.setProperty("oracle.net.CONNECT_TIMEOUT", "30000");
+		try {
+			final Properties oracle = new Properties();
+			CachedConnection.ConnectDialect.ORACLE.bound("jdbc:oracle:thin:@//h:1521/svc", oracle, 7);
+			assertNull(oracle.getProperty("oracle.net.CONNECT_TIMEOUT"), "the setting of the administrator was overridden");
+		} finally {
+			System.clearProperty("oracle.net.CONNECT_TIMEOUT");
+		}
+
+		// a plain name is common enough to be somebody else's system property: only a name a
+		// driver of these actually reads out of them is one of the administrator's
+		System.setProperty("socketTimeout", "30000");
+		try {
+			final Properties mysql = new Properties();
+			assertTrue(CachedConnection.ConnectDialect.MYSQL.bound("jdbc:mysql://h:3306/db", mysql, 7));
+			assertEquals(mysql.getProperty("socketTimeout"), "7000");
+		} finally {
+			System.clearProperty("socketTimeout");
+		}
+	}
+
+	/**
+	 * ... and a dotted name is not a name a driver reads out of the system properties by the shape
+	 * of it. ojdbc8 resolves oracle.jdbc.ReadTimeout and oracle.net.CONNECT_TIMEOUT in three tiers
+	 * (the properties it was supplied, then System.getProperty, then the properties of the data
+	 * source), while oracle.net.READ_TIMEOUT - a dotted name of the same driver, and the name the
+	 * socket option is finally read under - reaches the socket from the connection properties
+	 * alone: the classes carrying the literal hand it to Properties.get, none of them to
+	 * System.getProperty. Taken for a bound of the administrator, a -D of it leaves the login with
+	 * no read bound whatever: theirs is not read and ours is not set.
+	 */
+	@Test
+	public void testASystemPropertyNoDriverReadsIsNoBound() throws Exception {
+		System.setProperty("oracle.net.READ_TIMEOUT", "30000");
+		try {
+			final Properties oracle = new Properties();
+			assertTrue(CachedConnection.ConnectDialect.ORACLE.bound("jdbc:oracle:thin:@//h:1521/svc", oracle, 7),
+				"a -D the driver never reads left this login with no read bound at all");
+			assertEquals(oracle.getProperty("oracle.jdbc.ReadTimeout"), "7000");
+		} finally {
+			System.clearProperty("oracle.net.READ_TIMEOUT");
+		}
+
+		// ... while the same name written into the connection string is one the driver does read
+		final Properties declared = new Properties();
+		assertFalse(CachedConnection.ConnectDialect.ORACLE.bound(
+			"jdbc:oracle:thin:@(DESCRIPTION=(READ_TIMEOUT=30)(ADDRESS=(HOST=h)(PORT=1521)))", declared, 7));
+		assertNull(declared.getProperty("oracle.jdbc.ReadTimeout"));
+	}
+
+	/**
+	 * A property the administrator set to 0 is not a bound of theirs: every one of these drivers
+	 * reads 0 as "wait as long as it takes", which is the default this class exists to replace -
+	 * and on the three whose driver lets a supplied property win, ours is set on top of it.
+	 * Postgresql is the one where it cannot be, and is covered on its own below.
+	 */
+	@Test
+	public void testAZeroIsNotABoundOfTheAdministrator() throws Exception {
+		final Properties mysql = new Properties();
+		CachedConnection.ConnectDialect.MYSQL.bound("jdbc:mysql://h:3306/db?connectTimeout=0&socketTimeout=0", mysql, 7);
+		assertEquals(mysql.getProperty("connectTimeout"), "7000");
+		assertEquals(mysql.getProperty("socketTimeout"), "7000");
+
+		// ... and neither is a property left without a value
+		final Properties microsoft = new Properties();
+		CachedConnection.ConnectDialect.MICROSOFT.bound("jdbc:sqlserver://h:1433;socketTimeout=;databaseName=db", microsoft, 7);
+		assertEquals(microsoft.getProperty("socketTimeout"), "7000");
+
+		// the same of a system property, and of the descriptor of an oracle url
+		System.setProperty("oracle.jdbc.ReadTimeout", "0");
+		try {
+			final Properties oracle = new Properties();
+			assertTrue(CachedConnection.ConnectDialect.ORACLE.bound(
+				"jdbc:oracle:thin:@(DESCRIPTION=(READ_TIMEOUT=0)(ADDRESS=(HOST=h)(PORT=1521)))", oracle, 7));
+			assertEquals(oracle.getProperty("oracle.jdbc.ReadTimeout"), "7000");
+		} finally {
+			System.clearProperty("oracle.jdbc.ReadTimeout");
+		}
+
+		// a value that is no number is left to the driver it belongs to: it is not this class's to read
+		final Properties unreadable = new Properties();
+		assertFalse(CachedConnection.ConnectDialect.MYSQL.bound(
+			"jdbc:mysql://h:3306/db?socketTimeout=PT30S", unreadable, 7));
+		assertNull(unreadable.getProperty("socketTimeout"));
+	}
+
+	/**
+	 * On postgresql a parameter of the url outranks the property this class supplies: Driver
+	 * .connect copies what it was handed into a flat map and parseURL then writes the parameters of
+	 * the url on top of it. So a "socketTimeout=0" there cannot be replaced, and setting ours
+	 * regardless would leave this class believing it bounded a login that carries no bound - and
+	 * lifting a read bound after it that was never in force. The effective values are read back
+	 * through the parser of the driver itself, since asserting on the map handed to it is
+	 * asserting on the half of the story this bug lived in.
+	 */
+	@Test
+	public void testAParameterOfAPostgresUrlOutranksTheBoundOfThisClass() throws Exception {
+		final String url = "jdbc:postgresql://h:5432/db?connectTimeout=0&socketTimeout=0&loginTimeout=0";
+		final Properties supplied = new Properties();
+		assertFalse(CachedConnection.ConnectDialect.POSTGRES.bound(url, supplied, 7),
+			"a read bound that never reaches the driver must not be reported as one to lift");
+		assertNull(supplied.getProperty("socketTimeout"));
+		assertNull(supplied.getProperty("connectTimeout"));
+		assertNull(supplied.getProperty("loginTimeout"));
+
+		final Properties effective = org.postgresql.Driver.parseURL(url, supplied);
+		assertEquals(effective.getProperty("socketTimeout"), "0", "the url is what the driver ends up reading");
+		assertEquals(effective.getProperty("connectTimeout"), "0");
+		assertEquals(effective.getProperty("loginTimeout"), "0");
+	}
+
+	/**
+	 * The connect side of a dialect is one budget rather than a set of independent knobs, so a
+	 * bound of the administrator under any of its names leaves all of them alone. On postgresql
+	 * connectTimeout bounds the socket connect and loginTimeout the login behind it: filling in the
+	 * one they left out caps the one they set, since Driver.connect hands the login to a thread of
+	 * its own as soon as loginTimeout is anything but 0 and gives up on it there.
+	 */
+	@Test
+	public void testAConnectBudgetOfTheAdministratorIsNotCappedByThisClass() throws Exception {
+		final String url = "jdbc:postgresql://h:5432/db?connectTimeout=300";
+		final Properties supplied = new Properties();
+		assertTrue(CachedConnection.ConnectDialect.POSTGRES.bound(url, supplied, 30),
+			"the read bound is a budget of its own and is still set");
+		assertNull(supplied.getProperty("loginTimeout"),
+			"a loginTimeout of ours caps the connectTimeout the administrator set");
+		assertNull(supplied.getProperty("connectTimeout"));
+		assertEquals(supplied.getProperty("socketTimeout"), "30");
+
+		final Properties effective = org.postgresql.Driver.parseURL(url, supplied);
+		assertEquals(effective.getProperty("connectTimeout"), "300", "the budget of the administrator, in full");
+		assertNull(effective.getProperty("loginTimeout"), "nothing of ours hands this login to a thread to abandon");
+	}
+
+	/**
+	 * The bound handed to a driver stays inside the range an int of milliseconds takes. Where the
+	 * per-attempt property is off, the attempt takes what is left of the deadline of the borrow,
+	 * and the pool timeout has no upper bound of its own - while the SQL Server driver rejects a
+	 * socketTimeout past Integer.MAX_VALUE outright, failing every connect of that backend with
+	 * the name of a property nobody typed.
+	 */
+	@Test(timeOut = 120000)
+	public void testTheBoundHandedToADriverStaysInTheRangeAnIntTakes() throws Exception {
+		final long deadline = System.currentTimeMillis() + 3000000L * 1000; // 34 days: past 2^31 ms
+		assertEquals(CachedConnection.attemptSeconds(0, deadline), Integer.MAX_VALUE / 1000);
+
+		System.setProperty(CachedConnection.CONNECT_TIMEOUT_PROPERTY, "0");
+		System.setProperty(CachedConnection.POOL_TIMEOUT_PROPERTY, "3000000");
+		// a socket that answers the connect and closes it, rather than a port bound and released:
+		// with every bound of this borrow turned off, anything taking that port in between would
+		// leave the test hanging on the timeOut instead of failing
+		try (final ServerSocket rejecting = rejectingSocket()) {
+			final String url = "jdbc:sqlserver://127.0.0.1:" + rejecting.getLocalPort()
+				+ ";databaseName=opendj;user=opendj;password=opendj;encrypt=false";
+			final long startedAt = System.currentTimeMillis();
+			try {
+				CachedConnection.getConnection(url);
+				fail("a connect the database closes must be reported");
+			} catch (SQLException expected) {
+				assertFalse(expected.getMessage().contains("socketTimeout"),
+					"the driver was handed a bound it does not take: " + expected.getMessage());
+			}
+			assertElapsedWithinBound(startedAt, 0);
+		}
+	}
+
+	/** The clamp of the range holds where the borrow has no deadline to take it from either. */
+	@Test
+	public void testTheBoundOfAnAttemptStaysInRangeWithoutADeadline() throws Exception {
+		assertEquals(CachedConnection.attemptSeconds(Long.MAX_VALUE, Long.MAX_VALUE), Integer.MAX_VALUE / 1000);
+		assertEquals(CachedConnection.attemptSeconds(0, Long.MAX_VALUE), 0, "0 stands for an attempt with no bound");
+		assertEquals(CachedConnection.attemptSeconds(30, Long.MAX_VALUE), 30);
+	}
+
+	/** The connection string holds the credentials of the backend: a stall report must not carry them. */
+	@Test
+	public void testLoggedConnectionStringCarriesNoCredentials() throws Exception {
+		assertEquals(CachedConnection.safeUrl("jdbc:postgresql://h:5432/db?user=u&password=secret"), "jdbc:postgresql://h:5432/db");
+		// the parameter naming the database stays: two backends of one sql server host answer to
+		// the same url up to it, and a stall report that cannot tell them apart is one of neither
+		assertEquals(CachedConnection.safeUrl("jdbc:sqlserver://h:1433;databaseName=db;password=secret"),
+			"jdbc:sqlserver://h:1433;databaseName=db");
+		// ... and the token naming the kind of oracle driver stays as well: thin against oci is a
+		// first question of an oracle connect, and it stands in front of the credentials
+		assertEquals(CachedConnection.safeUrl("jdbc:oracle:thin:scott/secret@//h:1521/svc"), "jdbc:oracle:thin:@//h:1521/svc");
+		assertEquals(CachedConnection.safeUrl("jdbc:mysql://u:secret@h:3306/db"), "jdbc:mysql://h:3306/db");
+		assertEquals(CachedConnection.safeUrl("jdbc:oracle:thin:@//h:1521/svc"), "jdbc:oracle:thin:@//h:1521/svc");
+		// a password holding the parameter separator of another dialect: ";" separates nothing on
+		// an oracle url, so the credentials are cut in front of the "@" rather than inside them
+		assertEquals(CachedConnection.safeUrl("jdbc:oracle:thin:scott/pa;ss@//h:1521/svc"), "jdbc:oracle:thin:@//h:1521/svc");
+		// ... and one holding a ":" is cut in front of it too: the token of the driver is the one
+		// behind the subprotocol, not the last one standing in front of the "@"
+		assertEquals(CachedConnection.safeUrl("jdbc:oracle:thin:scott/pa:ss@//h:1521/svc"), "jdbc:oracle:thin:@//h:1521/svc");
+		// ... and an "@" that stands inside a parameter is not the end of credentials: the host survives
+		assertEquals(CachedConnection.safeUrl("jdbc:postgresql://h:5432/db?user=u@example.com&password=secret"),
+			"jdbc:postgresql://h:5432/db");
+		// a password holding the parameter separator of its own dialect: on an oracle url the
+		// parameters stand behind the descriptor, so a "?" in front of the "@" is part of the
+		// password and cutting there would leave the start of it in the log
+		assertEquals(CachedConnection.safeUrl("jdbc:oracle:thin:scott/pa?ss@//h:1521/svc"), "jdbc:oracle:thin:@//h:1521/svc");
+		// the same inside an authority, where the credentials end at the path rather than at a "?"
+		assertEquals(CachedConnection.safeUrl("jdbc:mysql://u:sec?ret@h:3306/db"), "jdbc:mysql://h:3306/db");
+		// a descriptor of an oracle url carries no credentials and survives whole
+		assertEquals(CachedConnection.safeUrl("jdbc:oracle:thin:@(DESCRIPTION=(ADDRESS=(HOST=h)(PORT=1521)))"),
+			"jdbc:oracle:thin:@(DESCRIPTION=(ADDRESS=(HOST=h)(PORT=1521)))");
+		// a first host with nothing in front of the comma keeps the comma: what is left is the
+		// hosts of a url, not one host of it
+		assertEquals(CachedConnection.safeUrl("jdbc:mysql://,h2:3306/db"), "jdbc:mysql://,h2:3306/db");
+		// a password under a name of its own, and one numbered by the factor it belongs to
+		assertEquals(CachedConnection.safeUrl("jdbc:mysql://(host=h,user=u,password2=secret)/db"),
+			"jdbc:mysql://(host=h,user=u,password2=***)/db");
+
+		// a url of Connector/J gives every host of it credentials of its own, and every one of
+		// them goes: the second used to stay in the message with the password of the failover host
+		assertEquals(CachedConnection.safeUrl("jdbc:mysql://u:p@h1:3306,u2:p2@h2:3306/db"),
+			"jdbc:mysql://h1:3306,h2:3306/db");
+		// ... including a url whose subprotocol names the kind of connection in front of the hosts
+		assertEquals(CachedConnection.safeUrl("jdbc:mysql:replication://master:p1@h1:3306,slave:p2@h2:3306/db"),
+			"jdbc:mysql:replication://h1:3306,h2:3306/db");
+		// the key-value host syntax of Connector/J puts the credentials inside the authority, where
+		// neither the userinfo nor the parameters of a url stand
+		assertEquals(CachedConnection.safeUrl("jdbc:mysql://address=(host=h)(port=3306)(user=u)(password=secret)/db"),
+			"jdbc:mysql://address=(host=h)(port=3306)(user=u)(password=***)/db");
+		assertEquals(CachedConnection.safeUrl("jdbc:mysql://(host=h,port=3306,user=u,password=secret)/db"),
+			"jdbc:mysql://(host=h,port=3306,user=u,password=***)/db");
+		assertEquals(CachedConnection.safeUrl("jdbc:sqlserver://h:1433;databaseName=db;PWD=secret"),
+			"jdbc:sqlserver://h:1433;databaseName=db");
+
+		// a shape none of this took apart is not logged past its subprotocol: a password holding a
+		// "/" ends the authority in front of the "@" that would have given the credentials away
+		assertEquals(CachedConnection.safeUrl("jdbc:mysql://u:pa/ss@h:3306/db"),
+			"jdbc:mysql:" + CachedConnection.CREDENTIALS_HIDDEN);
+		// ... and so does a password that holds an "@" and was quoted for the driver
+		assertEquals(CachedConnection.safeUrl("jdbc:oracle:thin:scott/\"pa@ss\"@//h:1521/svc"),
+			"jdbc:oracle:" + CachedConnection.CREDENTIALS_HIDDEN);
+		// a string that is no connection string of any driver carries nothing to the log either
+		assertEquals(CachedConnection.safeUrl("h:5432/db?password=secret"), CachedConnection.CREDENTIALS_HIDDEN);
+	}
+
+	/**
+	 * A driver is free to quote the connection string it was handed back into the message of its
+	 * failure, and that message travels: RootContainer makes it the message of what it throws,
+	 * BackendConfigManager logs it at ERROR and answers a config change with it. So the message is
+	 * redacted rather than the two call sites that happen to log a url.
+	 */
+	@Test
+	public void testAMessageOfADriverCarriesNoCredentials() throws Exception {
+		final String url = "jdbc:postgresql://opendj:S3cret@h:5432/db";
+		assertEquals(CachedConnection.redact("No suitable driver found for " + url, url),
+			"No suitable driver found for jdbc:postgresql://h:5432/db");
+		// a driver naming the credentials alone, without the url around them
+		assertEquals(CachedConnection.redact("authentication of opendj:S3cret failed", url),
+			"authentication of " + CachedConnection.CREDENTIALS_HIDDEN + " failed");
+		// ... and naming the password alone
+		assertEquals(CachedConnection.redact("the password S3cret was not accepted", url),
+			"the password " + CachedConnection.CREDENTIALS_HIDDEN + " was not accepted");
+		// the credentials of an oracle url stand in front of its descriptor
+		final String oracle = "jdbc:oracle:thin:scott/S3cret@//h:1521/svc";
+		assertEquals(CachedConnection.redact("IO Error connecting to " + oracle, oracle),
+			"IO Error connecting to jdbc:oracle:thin:@//h:1521/svc");
+		// a password of a parameter is blanked wherever the message carries it
+		assertEquals(CachedConnection.redact("bad url jdbc:sqlserver://h:1433;password=S3cret",
+			"jdbc:sqlserver://h:1433;password=S3cret"), "bad url jdbc:sqlserver://h:1433");
+		// a message naming nothing of the connection string is left as it stands
+		assertEquals(CachedConnection.redact("Connection to h:5432 refused", url), "Connection to h:5432 refused");
+		assertNull(CachedConnection.redact(null, url));
+
+		// the stall report is the other way a driver's message reaches the log, and it carries the
+		// url of the backend alongside it
+		final String stall = CachedConnection.stallMessage(url, 3, 4000,
+			new SQLException("FATAL: too many connections for " + url));
+		assertFalse(stall.contains("S3cret"), stall);
+		assertTrue(stall.contains("jdbc:postgresql://h:5432/db"), stall);
+		assertTrue(stall.contains("4000 ms") && stall.contains("(3 attempts)"), stall);
+	}
+
+	/**
+	 * A password is free to be one character long, and a bare one of those stands inside half the
+	 * lines a driver writes. Replaced wherever it is found, it takes the diagnostic apart along
+	 * with the credential - and, since the walk looking for credentials asks the redaction whether
+	 * it changed anything, it makes every failure of that backend one whose chain is rebuilt.
+	 */
+	@Test
+	public void testAShortPasswordDoesNotRewriteTheMessageOfADriver() throws Exception {
+		final String url = "jdbc:oracle:thin:opendj/1@//h:1521/svc";
+		// the "1" of an ORA number is part of a number, not a credential of anybody
+		assertEquals(CachedConnection.redact("ORA-12541: TNS:no listener", url), "ORA-12541: TNS:no listener");
+		// ... while the same password quoted back on its own is still taken out
+		assertEquals(CachedConnection.redact("the password 1 was not accepted", url),
+			"the password " + CachedConnection.CREDENTIALS_HIDDEN + " was not accepted");
+		assertEquals(CachedConnection.redact("IO Error connecting to " + url, url),
+			"IO Error connecting to jdbc:oracle:thin:@//h:1521/svc");
+	}
+
+	/**
+	 * A driver is free to name a parameter in the middle of a sentence. The value of one ends at
+	 * the first space: reaching to the end of the string, it would take the host, the port and the
+	 * cause of the failure into the blank along with the password - the very information the
+	 * redaction of a connection string goes out of its way to keep.
+	 */
+	@Test
+	public void testAPasswordParameterDoesNotSwallowTheRestOfTheMessage() throws Exception {
+		final String url = "jdbc:postgresql://h:5432/db?user=u&password=hunter2";
+		assertEquals(CachedConnection.redact("Connection refused: password=hunter2 for user u at h:5432", url),
+			"Connection refused: password=*** for user u at h:5432");
+	}
+
+	/**
+	 * The credentials of an oracle url are separated by a "/", so a password holding a "//" of
+	 * its own used to start an authority inside itself: what was taken off as a userinfo was the
+	 * tail of the password, the "@" the last guard of safeUrl() looks for went with it, and the
+	 * user name and the head of the password stayed in the message of a stall.
+	 */
+	@Test
+	public void testAPasswordHoldingASlashPairIsNotLeftInTheLog() throws Exception {
+		final String easyConnect = "jdbc:oracle:thin:opendj/pa//ss@//h:1521/svc";
+		assertEquals(CachedConnection.safeUrl(easyConnect), "jdbc:oracle:thin:@//h:1521/svc");
+		// ... and the same password in front of a host that names no "//" of its own
+		final String sid = "jdbc:oracle:thin:opendj/pa//ss@h:1521:svc";
+		assertEquals(CachedConnection.safeUrl(sid), "jdbc:oracle:thin:@h:1521:svc");
+		// the message of a driver quoting the url back carries no more of it than the log does
+		assertEquals(CachedConnection.redact("IO Error connecting to " + easyConnect, easyConnect),
+			"IO Error connecting to jdbc:oracle:thin:@//h:1521/svc");
+	}
+
+	/**
+	 * pgjdbc enforces loginTimeout out of process: Driver.connect hands the login to a daemon
+	 * thread of its own and gives up on the thread rather than on the login. Against the database
+	 * this bound exists for - one that completes the handshake and then says nothing - an
+	 * unbounded read there leaves that thread, and the socket it holds, behind on every borrow;
+	 * a few operations a second are enough to run the server out of threads and file descriptors.
+	 */
+	@Test(timeOut = 300000)
+	public void testTheLoginThreadOfPostgresDoesNotOutliveTheBorrow() throws Exception {
+		System.setProperty(CachedConnection.CONNECT_TIMEOUT_PROPERTY, Long.toString(BOUND_SECONDS));
+		// counted as a delta of this borrow rather than as a count of the jvm: three tests of this
+		// file open a pgjdbc login against a socket that never answers, and the order they run in
+		// is not contractual - a thread left by any of them would be reported here
+		final int before = loginThreadsOfPostgres();
+		try (final ServerSocket blackhole = new ServerSocket(0, 50, InetAddress.getLoopbackAddress())) {
+			final String url = "jdbc:postgresql://127.0.0.1:" + blackhole.getLocalPort() + "/opendj?user=opendj&password=opendj";
+			try {
+				CachedConnection.getConnection(url);
+				fail("a database that never answers must not hand out a connection");
+			} catch (SQLException expected) {
+				// reported to the caller, as the bound of the attempt promises
+			}
+			final long giveUpAt = System.currentTimeMillis() + BOUND_SECONDS * 1000 + BOUND_MARGIN_MS;
+			while (loginThreadsOfPostgres() > before && System.currentTimeMillis() < giveUpAt) {
+				Thread.sleep(100);
+			}
+			assertTrue(loginThreadsOfPostgres() <= before,
+				"the login thread pgjdbc abandoned outlived the borrow: the read of the login is not bounded");
+		}
+	}
+
+	private static int loginThreadsOfPostgres() {
+		int alive = 0;
+		for (final Thread thread : Thread.getAllStackTraces().keySet()) {
+			if (thread.isAlive() && thread.getName().startsWith("PostgreSQL JDBC driver connection thread")) {
+				alive++;
+			}
+		}
+		return alive;
+	}
+
+	/**
+	 * The deadline of the borrow stands for the whole borrow, so it bounds the attempt inside it
+	 * even where the per-attempt property gives it no bound of its own: turning that property off
+	 * must not turn the bound of the borrow off with it.
+	 */
+	@Test(timeOut = 300000)
+	public void testTheDeadlineBoundsAnAttemptTheConnectPropertyDoesNot() throws Exception {
+		System.setProperty(CachedConnection.CONNECT_TIMEOUT_PROPERTY, "0");
+		System.setProperty(CachedConnection.POOL_TIMEOUT_PROPERTY, "2");
+		try (final ServerSocket blackhole = new ServerSocket(0, 50, InetAddress.getLoopbackAddress())) {
+			final String url = "jdbc:postgresql://127.0.0.1:" + blackhole.getLocalPort() + "/opendj?user=opendj&password=opendj";
+			final long startedAt = System.currentTimeMillis();
+			try {
+				CachedConnection.getConnection(url);
+				fail("a database that never answers must not hand out a connection");
+			} catch (SQLException expected) {
+				// bounded by what is left of the deadline of the borrow
+			}
+			// the wait is the point of this one as much as its end is: a borrow against a socket that
+			// never answers cannot be over before the deadline unless something else ended it
+			final long elapsed = System.currentTimeMillis() - startedAt;
+			assertTrue(elapsed >= 1000, "the borrow was over after " + elapsed + " ms, before its deadline");
+			assertElapsedWithinBound(startedAt, 2000);
+		}
+	}
+
+	/**
+	 * The deadline stops the drain of the pool; it does not throw away the connection in hand. A
+	 * database at its connection limit has no other source of connections than the ones coming
+	 * back to the pool, and closing one unvalidated takes it out of that source for good - while
+	 * the borrow that closed it fails with a timeout anyway.
+	 */
+	@Test(timeOut = 120000)
+	public void testAPooledConnectionIsNotDiscardedUnvalidatedAtTheDeadline() throws Exception {
+		final String url = StubDriver.PREFIX + "unvalidated-at-deadline";
+		final Connection stale = mock(Connection.class);
+		when(stale.isValid(anyInt())).thenAnswer(invocation -> {
+			Thread.sleep(1500); // a database that no longer answers: the validation waits out its bound
+			return false;
+		});
+		final Connection good = mock(Connection.class);
+		when(good.isValid(anyInt())).thenReturn(true);
+		seedPool(url, stale, good);
+		final Connection fresh = mock(Connection.class);
+		stub.answerWith(fresh);
+		System.setProperty(CachedConnection.POOL_TIMEOUT_PROPERTY, "1");
+
+		final Connection borrowed = CachedConnection.getConnection(url);
+
+		assertSame(((CachedConnection) borrowed).parent, fresh, "the drain must stop at the deadline");
+		verify(stale).close();
+		verify(good, never()).close();
+		assertFalse(CachedConnection.cached.get(url).isEmpty(), "a connection the deadline was reached in front of was lost");
+	}
+
+	/**
+	 * A connection the validation of which failed is on its way out, and its driver knows it:
+	 * Connector/J answers a failed validation by aborting the connection and the SQL Server driver
+	 * by terminating it. Putting the previous bound back on it fails, and warns about statements
+	 * of a connection that is being closed - over an idle connection the server reaped, which is
+	 * nobody's problem.
+	 */
+	@Test(timeOut = 120000)
+	public void testAConnectionOnItsWayOutIsNotGivenItsBoundBack() throws Exception {
+		final String url = StubDriver.PREFIX + "reaped-idle";
+		final Connection reaped = mock(Connection.class);
+		when(reaped.getNetworkTimeout()).thenReturn(0);
+		when(reaped.isValid(anyInt())).thenReturn(false);
+		seedPool(url, reaped);
+		final Connection fresh = mock(Connection.class);
+		stub.answerWith(fresh);
+
+		assertSame(((CachedConnection) CachedConnection.getConnection(url)).parent, fresh);
+
+		verify(reaped).setNetworkTimeout(any(Executor.class), eq(CachedConnection.VALIDATION_TIMEOUT_SECONDS * 1000));
+		verify(reaped, never()).setNetworkTimeout(any(Executor.class), eq(0));
+		verify(reaped).close();
+	}
+
+	/**
+	 * The read bound of the login is lifted once the login is through, because left in place it
+	 * fails every statement slower than it. A driver that will not take it back leaves a
+	 * connection that must not be pooled: it would carry that bound into every borrow the pool
+	 * hands it to, an import batch among them.
+	 */
+	@Test(timeOut = 120000)
+	public void testAConnectionStillCarryingTheBoundOfItsLoginIsNotPooled() throws Exception {
+		final String url = StubDriver.PREFIX + "unliftable-bound";
+		final Connection parent = mock(Connection.class);
+		doThrow(new SQLException("setNetworkTimeout is not supported"))
+			.when(parent).setNetworkTimeout(any(Executor.class), eq(0));
+		stub.answerWith(parent);
+
+		final CachedConnection borrowed = CachedConnection.connect(url, CachedConnection.ConnectDialect.MYSQL, 30);
+		borrowed.close();
+
+		verify(parent).close();
+		assertTrue(CachedConnection.cached.get(url).isEmpty(),
+			"a connection still carrying the read bound of its login went back into the pool");
+	}
+
+	/**
+	 * The case the window exists for: the connection this borrow takes out answered the database a
+	 * moment ago, and asking it again costs the round trip the operation came to make.
+	 */
+	@Test(timeOut = 120000)
+	public void testAConnectionProvenAliveIsNotValidatedAgainWithinTheWindow() throws Exception {
+		final String url = StubDriver.PREFIX + "within-the-window";
+		CachedConnection.aliveBypassNanos = TimeUnit.HOURS.toNanos(1);
+		final Connection parent = mock(Connection.class);
+		when(parent.isValid(anyInt())).thenReturn(true);
+		stub.answerWith(parent);
+
+		final Connection first = CachedConnection.getConnection(url); // established: it has just answered
+		first.close();
+		final Connection second = CachedConnection.getConnection(url);
+
+		assertSame(second, first, "the pooled connection was not the one handed back");
+		assertEquals(stub.attempts.get(), 1, "the pool established a second connection");
+		verify(parent, never()).isValid(anyInt());
+	}
+
+	/** Past the window it is the connection the database or a firewall may have dropped meanwhile. */
+	@Test(timeOut = 120000)
+	public void testAConnectionIsValidatedAgainOnceTheWindowHasPassed() throws Exception {
+		final String url = StubDriver.PREFIX + "past-the-window";
+		CachedConnection.aliveBypassNanos = TimeUnit.MILLISECONDS.toNanos(1);
+		final Connection parent = mock(Connection.class);
+		when(parent.isValid(anyInt())).thenReturn(true);
+		stub.answerWith(parent);
+
+		final Connection first = CachedConnection.getConnection(url);
+		first.close();
+		Thread.sleep(20);
+		final Connection second = CachedConnection.getConnection(url);
+
+		assertSame(second, first);
+		verify(parent).isValid(CachedConnection.VALIDATION_TIMEOUT_SECONDS);
+	}
+
+	/** The window switched off validates every borrow, the way this pool did before it existed. */
+	@Test(timeOut = 120000)
+	public void testAWindowOfZeroValidatesEveryBorrow() throws Exception {
+		final String url = StubDriver.PREFIX + "window-of-zero";
+		CachedConnection.aliveBypassNanos = 0;
+		final Connection parent = mock(Connection.class);
+		when(parent.isValid(anyInt())).thenReturn(true);
+		stub.answerWith(parent);
+
+		final Connection first = CachedConnection.getConnection(url);
+		first.close();
+		final Connection second = CachedConnection.getConnection(url);
+
+		assertSame(second, first);
+		verify(parent).isValid(CachedConnection.VALIDATION_TIMEOUT_SECONDS);
+	}
+
+	/**
+	 * A connection is trusted for the window that follows the last answer it gave, never for the
+	 * window that follows its return to the pool. pgjdbc short-circuits both rollback() and
+	 * commit() when the transaction state is IDLE, so a borrow that issued no statement - the open
+	 * of a backend, a configuration change that leaves the base DNs alone, an import of nothing -
+	 * puts a connection back without a byte reaching the server: stamping the return would mark a
+	 * connection the database dropped meanwhile as the freshest one in the pool.
+	 */
+	@Test(timeOut = 120000)
+	public void testTheReturnToThePoolIsNotTakenForProofOfLife() throws Exception {
+		final String url = StubDriver.PREFIX + "silent-return";
+		CachedConnection.aliveBypassNanos = TimeUnit.MILLISECONDS.toNanos(50);
+		final Connection dropped = mock(Connection.class);
+		when(dropped.isValid(anyInt())).thenReturn(false); // dropped while it was out of the pool
+		stub.answerWith(dropped);
+
+		final Connection borrowed = CachedConnection.getConnection(url);
+		Thread.sleep(80); // the answer of the login ages out of the window
+		borrowed.close(); // and the rollback of this return never leaves the driver
+		final Connection fresh = mock(Connection.class);
+		when(fresh.isValid(anyInt())).thenReturn(true);
+		stub.answerWith(fresh);
+
+		final Connection next = CachedConnection.getConnection(url);
+
+		verify(dropped).isValid(CachedConnection.VALIDATION_TIMEOUT_SECONDS);
+		verify(dropped).close();
+		assertSame(((CachedConnection) next).parent, fresh,
+			"a connection the database dropped was handed out on the strength of its return to the pool");
+	}
+
+	/**
+	 * A proof taken while the database was going away does not outlive the distrust that reported it.
+	 * <p>
+	 * The stamp stands for the moment the connection was asked, not the moment its answer was filed:
+	 * a validation is given {@link CachedConnection#VALIDATION_TIMEOUT_SECONDS}, and one that started
+	 * before another operation reported a drop and returned after it would otherwise be the younger of
+	 * the two. The connection would then be handed out unvalidated for the rest of the window - and
+	 * LIFO puts it at the head of the deque, so it is the very one the next borrow takes - by the
+	 * check that exists to stop exactly that.
+	 */
+	@Test(timeOut = 120000)
+	public void testAProofTakenWhileTheDatabaseWentAwayIsNotTrusted() throws Exception {
+		final String url = StubDriver.PREFIX + "proof-across-a-drop";
+		CachedConnection.aliveBypassNanos = TimeUnit.HOURS.toNanos(1); // nothing here ages out of the window
+		final AtomicInteger validations = new AtomicInteger();
+		final Connection parent = mock(Connection.class);
+		// the database goes away while this validation is in flight: another operation of the backend
+		// reports the drop of its own connection before this one has answered
+		when(parent.isValid(anyInt())).thenAnswer(invocation -> {
+			CachedConnection.distrustPool(url);
+			validations.incrementAndGet();
+			return true;
+		});
+		stub.answerWith(parent);
+
+		CachedConnection.getConnection(url).close(); // established and returned, proven by its login
+		CachedConnection.distrustPool(url);          // an operation reports a drop: what the pool holds predates it
+		CachedConnection.getConnection(url).close(); // validated, and a second drop is reported while it is
+
+		final Connection borrowed = CachedConnection.getConnection(url);
+
+		assertEquals(validations.get(), 2,
+			"a connection was trusted on a proof that started before the drop it is compared against");
+		assertSame(((CachedConnection) borrowed).parent, parent, "the connection answered and was still discarded");
+	}
+
+	/**
+	 * The pool hands out the connection returned last. Without it the window would rarely apply: a
+	 * connection reached only after a whole cycle of the pool has been idle far longer than it.
+	 */
+	@Test(timeOut = 120000)
+	public void testTheConnectionReturnedLastIsBorrowedFirst() throws Exception {
+		final String url = StubDriver.PREFIX + "returned-last";
+		CachedConnection.aliveBypassNanos = TimeUnit.HOURS.toNanos(1);
+		final Connection older = mock(Connection.class);
+		when(older.isValid(anyInt())).thenReturn(true);
+		stub.answerWith(older);
+		final Connection first = CachedConnection.getConnection(url);
+		final Connection newer = mock(Connection.class);
+		when(newer.isValid(anyInt())).thenReturn(true);
+		stub.answerWith(newer);
+		final Connection second = CachedConnection.getConnection(url);
+		assertNotSame(second, first);
+		first.close();
+		second.close();
+
+		final Connection borrowed = CachedConnection.getConnection(url);
+
+		assertSame(((CachedConnection) borrowed).parent, newer, "the pool cycled round to its coldest connection");
+	}
+
+	/**
+	 * Whatever dropped one connection - a restart, a failover, a network that went away - dropped
+	 * every connection established before it, and a borrow inside the window asks the database
+	 * nothing: so the operation that saw the failure tells the pool, and the rest of that
+	 * generation is validated once before it is trusted again.
+	 */
+	@Test(timeOut = 120000)
+	public void testThePoolIsValidatedAgainAfterTheDatabaseDroppedAConnection() throws Exception {
+		final String url = StubDriver.PREFIX + "distrusted-generation";
+		CachedConnection.aliveBypassNanos = TimeUnit.HOURS.toNanos(1);
+		final Connection parent = mock(Connection.class);
+		when(parent.isValid(anyInt())).thenReturn(true);
+		stub.answerWith(parent);
+		CachedConnection.getConnection(url).close();
+
+		CachedConnection.distrustPool(url);
+		final Connection next = CachedConnection.getConnection(url);
+		next.close();
+		CachedConnection.getConnection(url).close();
+
+		// once for the generation the drop condemned, and not again for the borrow behind it
+		verify(parent, times(1)).isValid(CachedConnection.VALIDATION_TIMEOUT_SECONDS);
+	}
+
+	/**
+	 * The whole of the trade the window makes, end to end: a connection the database dropped
+	 * inside the window is handed out unvalidated - that is the cost - the operation it broke
+	 * reports the drop, and from there the pool validates the generation the drop condemned
+	 * instead of handing out the rest of it the same way.
+	 */
+	@Test(timeOut = 120000)
+	public void testAConnectionDroppedInsideTheWindowIsHandedOutOnceAndThenValidated() throws Exception {
+		final String url = StubDriver.PREFIX + "dropped-inside-the-window";
+		CachedConnection.aliveBypassNanos = TimeUnit.HOURS.toNanos(1);
+		final Connection parent = mock(Connection.class);
+		when(parent.isValid(anyInt())).thenReturn(true);
+		stub.answerWith(parent);
+		CachedConnection.getConnection(url).close();
+
+		when(parent.isValid(anyInt())).thenReturn(false); // the database dropped it where it lay
+		final Connection dropped = CachedConnection.getConnection(url);
+		assertSame(((CachedConnection) dropped).parent, parent, "the pooled connection was not the one handed back");
+		verify(parent, never()).isValid(anyInt()); // handed out on the strength of its last answer
+
+		// the statement of the caller is where the drop surfaces, and the caller reports it
+		CachedConnection.distrustPool(url);
+		dropped.close();
+		final Connection fresh = mock(Connection.class);
+		when(fresh.isValid(anyInt())).thenReturn(true);
+		stub.answerWith(fresh);
+
+		final Connection next = CachedConnection.getConnection(url);
+
+		verify(parent).isValid(CachedConnection.VALIDATION_TIMEOUT_SECONDS);
+		verify(parent).close();
+		assertSame(((CachedConnection) next).parent, fresh, "the rest of the generation was handed out unvalidated");
+	}
+
+	/**
+	 * Seeds the pool the way {@link CachedConnection#close()} fills it - at the end a borrow takes
+	 * from - so that the connection named first here is the one the next borrow gets.
+	 */
+	private static void seedPool(String url, Connection... parents) {
+		for (int i = parents.length - 1; i >= 0; i--) {
+			CachedConnection.cached.get(url).addFirst(new CachedConnection(url, parents[i]));
+		}
+	}
+
+	/**
+	 * The borrows nothing compensates a dropped connection on - the open of a backend, the removal
+	 * of its files, the start of an import - ask for a connection the pool validates whatever the
+	 * window says. Each of them is one borrow of a cold path, and the one that opens a backend
+	 * issues no statement at all: a connection dropped inside the window would surface there out of
+	 * the rollback that releases it, with no statement to replay and nothing to tell the pool.
+	 */
+	@Test(timeOut = 120000)
+	public void testTheBorrowsNothingCompensatesAreValidated() throws Exception {
+		final String url = StubDriver.PREFIX + "validated-borrow";
+		CachedConnection.aliveBypassNanos = TimeUnit.HOURS.toNanos(1);
+		final Connection parent = mock(Connection.class);
+		when(parent.isValid(anyInt())).thenReturn(true);
+		stub.answerWith(parent);
+		CachedConnection.getConnection(url).close();
+
+		final Connection borrowed = CachedConnection.getConnection(url, false);
+
+		assertSame(((CachedConnection) borrowed).parent, parent, "the pooled connection was not the one handed back");
+		verify(parent).isValid(CachedConnection.VALIDATION_TIMEOUT_SECONDS);
+	}
+
+	/**
+	 * A connection closed under the borrow is not handed out on the strength of its last answer:
+	 * the removal listener of the pool closes every connection it finds in the deque when the pool
+	 * expires, and it iterates a weakly consistent view. The validation the window replaces
+	 * answered that as well, out of a flag of the driver rather than out of a round trip.
+	 */
+	@Test(timeOut = 120000)
+	public void testAConnectionThePoolClosedIsNotHandedOut() throws Exception {
+		final String url = StubDriver.PREFIX + "closed-inside-the-window";
+		CachedConnection.aliveBypassNanos = TimeUnit.HOURS.toNanos(1);
+		final Connection parent = mock(Connection.class);
+		when(parent.isValid(anyInt())).thenReturn(true);
+		stub.answerWith(parent);
+		CachedConnection.getConnection(url).close();
+		// closed where it lay, by the expiry of the pool: a closed connection answers isValid() with
+		// false as well, which is what discards it once the window stops trusting it
+		when(parent.isClosed()).thenReturn(true);
+		when(parent.isValid(anyInt())).thenReturn(false);
+		final Connection fresh = mock(Connection.class);
+		when(fresh.isValid(anyInt())).thenReturn(true);
+		stub.answerWith(fresh);
+
+		final Connection borrowed = CachedConnection.getConnection(url);
+
+		assertSame(((CachedConnection) borrowed).parent, fresh, "a closed connection was handed out on its last answer");
+	}
+
+	/**
+	 * The window is clamped twice: to the idle time the pool keeps a connection for, since a window
+	 * longer than that is one the pool can never back - the connection it was meant for is gone
+	 * before it closes - and to {@link CachedConnection#MAX_ALIVE_BYPASS_MS} behind it, since the
+	 * ttl has no upper bound of its own and a value the unit conversion saturates on would leave
+	 * every connection of the pool trusted for the life of the server.
+	 * <p>
+	 * About the value the class settles on at initialization: the field the pool reads is assigned
+	 * once, so a ttl set after that changes neither it nor the idle time it was clamped to.
+	 */
+	@Test(timeOut = 120000)
+	public void testTheWindowIsClampedToTheIdleTimeOfThePool() {
+		System.setProperty(CachedConnection.TTL_PROPERTY, "15000");
+		System.setProperty(CachedConnection.ALIVE_BYPASS_PROPERTY, "500");
+		assertEquals(CachedConnection.getAliveBypassMillis(), 500L, "a window inside the ttl was not left alone");
+
+		System.setProperty(CachedConnection.ALIVE_BYPASS_PROPERTY, Long.toString(Long.MAX_VALUE));
+		assertEquals(CachedConnection.getAliveBypassMillis(), 15000L, "a window of Long.MAX_VALUE was not clamped");
+
+		System.setProperty(CachedConnection.TTL_PROPERTY, "100");
+		assertEquals(CachedConnection.getAliveBypassMillis(), 100L, "the clamp is the configured ttl, not the default");
+
+		// the ttl has no upper bound of its own, so the clamp to it does not bound the window either: both set
+		// to a value the conversion to nanoseconds saturates on would leave every connection of the pool
+		// trusted for the life of the server, which is the outcome this javadoc says the clamp rules out
+		System.setProperty(CachedConnection.TTL_PROPERTY, Long.toString(Long.MAX_VALUE));
+		System.setProperty(CachedConnection.ALIVE_BYPASS_PROPERTY, Long.toString(Long.MAX_VALUE));
+		assertEquals(CachedConnection.getAliveBypassMillis(), CachedConnection.MAX_ALIVE_BYPASS_MS,
+			"a window the ttl did not bound was left to saturate");
+	}
+
+	/**
+	 * A setting worth warning about must leave the class usable. Both properties are read by the
+	 * initializer of {@code aliveBypassNanos}, and both report an unusable value through the set of
+	 * what has been said once already - which, declared below that initializer, would still be null
+	 * when the initializer reaches it (JLS 12.4.2). A window longer than the ttl is exactly the
+	 * tuning the javadoc of the property invites, and it would turn a log line into an
+	 * ExceptionInInitializerError on the first borrow and a causeless NoClassDefFoundError on every
+	 * one after it: no connection can be borrowed, so the backend cannot open at all.
+	 * <p>
+	 * Asserted on the class loaded afresh rather than on this one, which was initialized long
+	 * before the property was set.
+	 */
+	@Test(timeOut = 120000, dataProvider = "settingsWorthWarningAbout")
+	public void testASettingWorthWarningAboutStillInitializesTheClass(String ttl, String window, long expectedMillis)
+			throws Exception {
+		System.setProperty(CachedConnection.TTL_PROPERTY, ttl);
+		System.setProperty(CachedConnection.ALIVE_BYPASS_PROPERTY, window);
+
+		final Class<?> reloaded = loadedAfresh(CachedConnection.class);
+
+		assertNotSame(reloaded, CachedConnection.class, "the class under test was not loaded afresh");
+		final Field field = reloaded.getDeclaredField("aliveBypassNanos");
+		field.setAccessible(true);
+		assertEquals(field.getLong(null), TimeUnit.MILLISECONDS.toNanos(expectedMillis),
+			"the window the reloaded class settled on");
+	}
+
+	@DataProvider
+	public Object[][] settingsWorthWarningAbout() {
+		return new Object[][]{
+			// a window longer than the ttl: reported once and used as the ttl
+			{"15000", "60000", 15000L},
+			// not a number, and negative: reported once and ignored in favour of the default
+			{"15000", "half a second", CachedConnection.DEFAULT_ALIVE_BYPASS_MS},
+			{"15000", "-1", CachedConnection.DEFAULT_ALIVE_BYPASS_MS},
+			// the ttl is read by the same initializer, and reports its own value the same way
+			{"30s", "500", 500L}
+		};
+	}
+
+	/**
+	 * The class again, defined by a loader of this test rather than taken from the one that has
+	 * already initialized it: a static initializer runs once per loader, and this is about what it
+	 * does. Every other class is delegated to the parent, so the reloaded one shares the types it
+	 * is written against.
+	 */
+	private static Class<?> loadedAfresh(Class<?> type) throws Exception {
+		final String name = type.getName();
+		final ClassLoader parent = type.getClassLoader();
+		final ClassLoader loader = new ClassLoader(parent) {
+			@Override
+			protected Class<?> loadClass(String candidate, boolean resolve) throws ClassNotFoundException {
+				if (!name.equals(candidate)) {
+					return super.loadClass(candidate, resolve);
+				}
+				Class<?> defined = findLoadedClass(candidate);
+				if (defined == null) {
+					final byte[] bytecode = bytecodeOf(candidate, parent);
+					defined = defineClass(candidate, bytecode, 0, bytecode.length);
+				}
+				if (resolve) {
+					resolveClass(defined);
+				}
+				return defined;
+			}
+		};
+		return Class.forName(name, true, loader);
+	}
+
+	private static byte[] bytecodeOf(String name, ClassLoader from) throws ClassNotFoundException {
+		try (final InputStream in = from.getResourceAsStream(name.replace('.', '/') + ".class")) {
+			if (in == null) {
+				throw new ClassNotFoundException(name);
+			}
+			final ByteArrayOutputStream bytecode = new ByteArrayOutputStream();
+			final byte[] chunk = new byte[8192];
+			for (int read; (read = in.read(chunk)) >= 0; ) {
+				bytecode.write(chunk, 0, read);
+			}
+			return bytecode.toByteArray();
+		} catch (IOException e) {
+			throw new ClassNotFoundException(name, e);
+		}
+	}
+
+	private static SQLException tooManyConnections() {
+		// 53300, too_many_connections, of the insufficient_resources class
+		return new SQLException("sorry, too many clients already", "53300");
+	}
+
+	/** A connection string of every dialect pointing at one host and port. */
+	private static String[] urlsOf(int port) {
+		return new String[]{
+			"jdbc:postgresql://127.0.0.1:" + port + "/opendj?user=opendj&password=opendj",
+			"jdbc:mysql://127.0.0.1:" + port + "/opendj?user=opendj&password=opendj",
+			"jdbc:oracle:thin:opendj/opendj@//127.0.0.1:" + port + "/free",
+			"jdbc:sqlserver://127.0.0.1:" + port + ";databaseName=opendj;user=opendj;password=opendj;encrypt=false"
+		};
+	}
+
+	private static int closedPort() throws Exception {
+		try (final ServerSocket socket = new ServerSocket(0, 1, InetAddress.getLoopbackAddress())) {
+			return socket.getLocalPort();
+		} // closed again: nothing listens there any more
+	}
+
+	/**
+	 * A socket that answers a connect and closes it at once. A port bound and released is the
+	 * shape of a refused connect a test would reach for, but it races whatever else on the host
+	 * may take that port; this one is the failure it stands for and belongs to nobody else.
+	 */
+	private static ServerSocket rejectingSocket() throws Exception {
+		final ServerSocket socket = new ServerSocket(0, 50, InetAddress.getLoopbackAddress());
+		final Thread accepting = new Thread(() -> {
+			while (!socket.isClosed()) {
+				try {
+					socket.accept().close();
+				} catch (Exception closed) {
+					return;
+				}
+			}
+		}, "opendj-test-rejecting-socket");
+		accepting.setDaemon(true);
+		accepting.start();
+		return socket;
+	}
+
+	// The margin grows with the bound instead of dwarfing it: what this has to catch is a bound
+	// that is not in force, and a bound of 2 s that is not in force is not a wait of 12 s - it is
+	// the 30 s of the connect property, the 600 s of a driver, or no end at all.
+	private static void assertElapsedWithinBound(long startedAt, long boundMs) {
+		final long elapsed = System.currentTimeMillis() - startedAt;
+		final long margin = Math.max(BOUND_MARGIN_MS, boundMs);
+		assertTrue(elapsed < boundMs + margin,
+			"gave up only after " + elapsed + " ms, past the " + boundMs + " ms it was bounded by");
+	}
+
+	/**
+	 * Stands in for a database whose answer to a connect is the point of the test: the vendor
+	 * codes and SQL states below are what the retry has to tell apart, and no engine is needed to
+	 * produce them.
+	 */
+	private static final class StubDriver implements Driver {
+		static final String PREFIX = "jdbc:opendj-stub:";
+		static final int ALWAYS = -1;
+
+		final AtomicInteger attempts = new AtomicInteger();
+		private volatile SQLException failure;
+		private volatile int failuresLeft;
+		private volatile Connection answer;
+
+		void failWith(SQLException failure, int times) {
+			this.failure = failure;
+			this.failuresLeft = times;
+			this.answer = null;
+			this.attempts.set(0);
+		}
+
+		void answerWith(Connection answer) {
+			this.failure = null;
+			this.failuresLeft = 0;
+			this.answer = answer;
+			this.attempts.set(0);
+		}
+
+		@Override
+		public Connection connect(String url, Properties info) throws SQLException {
+			if (!acceptsURL(url)) {
+				return null;
+			}
+			attempts.incrementAndGet();
+			if (failuresLeft != 0) {
+				if (failuresLeft > 0) {
+					failuresLeft--;
+				}
+				throw failure;
+			}
+			if (answer != null) {
+				return answer;
+			}
+			final Connection con = mock(Connection.class);
+			when(con.isValid(anyInt())).thenReturn(true);
+			return con;
+		}
+
+		@Override
+		public boolean acceptsURL(String url) {
+			return url != null && url.startsWith(PREFIX);
+		}
+
+		@Override
+		public DriverPropertyInfo[] getPropertyInfo(String url, Properties info) {
+			return new DriverPropertyInfo[0];
+		}
+
+		@Override
+		public int getMajorVersion() {
+			return 1;
+		}
+
+		@Override
+		public int getMinorVersion() {
+			return 0;
+		}
+
+		@Override
+		public boolean jdbcCompliant() {
+			return false;
+		}
+
+		@Override
+		public Logger getParentLogger() {
+			return Logger.getLogger(StubDriver.class.getName());
+		}
+	}
+}
diff --git a/opendj-server-legacy/src/test/java/org/opends/server/backends/jdbc/JDBCStorageRetryTest.java b/opendj-server-legacy/src/test/java/org/opends/server/backends/jdbc/JDBCStorageRetryTest.java
index 93d33f2..487f36d 100644
--- a/opendj-server-legacy/src/test/java/org/opends/server/backends/jdbc/JDBCStorageRetryTest.java
+++ b/opendj-server-legacy/src/test/java/org/opends/server/backends/jdbc/JDBCStorageRetryTest.java
@@ -20,34 +20,64 @@
 import org.opends.server.backends.jdbc.JDBCStorage.Conflict;
 import org.opends.server.backends.pluggable.spi.AccessMode;
 import org.opends.server.backends.pluggable.spi.StorageRuntimeException;
+import org.opends.server.backends.pluggable.spi.TreeName;
 import org.opends.server.backends.pluggable.spi.WriteOperation;
 import org.opends.server.backends.pluggable.spi.WriteableTransaction;
 import org.opends.server.types.DirectoryException;
+import org.testng.annotations.AfterClass;
+import org.testng.annotations.BeforeClass;
 import org.testng.annotations.DataProvider;
 import org.testng.annotations.Test;
 
 import java.sql.Connection;
+import java.sql.DatabaseMetaData;
+import java.sql.Driver;
+import java.sql.DriverManager;
+import java.sql.DriverPropertyInfo;
+import java.sql.PreparedStatement;
+import java.sql.ResultSet;
 import java.sql.SQLException;
+import java.sql.SQLNonTransientConnectionException;
+import java.sql.SQLRecoverableException;
+import java.sql.Statement;
+import java.util.Properties;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.logging.Logger;
 
 import static org.forgerock.i18n.LocalizableMessage.raw;
 import static org.forgerock.opendj.ldap.ResultCode.OTHER;
+import static org.mockito.Mockito.any;
+import static org.mockito.Mockito.anyBoolean;
+import static org.mockito.Mockito.anyInt;
+import static org.mockito.Mockito.anyString;
+import static org.mockito.Mockito.doNothing;
+import static org.mockito.Mockito.doThrow;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.startsWith;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
 import static org.opends.server.backends.jdbc.JDBCStorage.Conflict.AFTER_LOCK_WAIT;
 import static org.opends.server.backends.jdbc.JDBCStorage.Conflict.NONE;
 import static org.opends.server.backends.jdbc.JDBCStorage.Conflict.PROMPT;
 import static org.testng.Assert.assertEquals;
+import static org.testng.Assert.assertFalse;
+import static org.testng.Assert.assertNull;
 import static org.testng.Assert.assertSame;
 import static org.testng.Assert.assertTrue;
+import static org.testng.Assert.fail;
 
 /**
- * Tests how a failure is classified as a transaction conflict, which is what decides whether
- * {@link JDBCStorage#write} replays the operation and whether its first replay is granted regardless of the
- * clock, how long the replays may go on for, and how long it waits before each of them.
+ * Tests how a failure is classified - as a transaction conflict of one class or another, or as a connection the
+ * database dropped - which is what decides whether {@link JDBCStorage#write} replays the operation, whether its
+ * first replay is granted regardless of the clock, how long the replays may go on for and how long it waits
+ * before each of them; and what {@code write()} itself does with that verdict, replay and pool alike.
  * <p>
  * Runs without a database: the failures the drivers report are reproduced as synthetic
- * {@link SQLException}s carrying the same vendor error number and SQLState.
+ * {@link SQLException}s carrying the same vendor error number and SQLState, and the writes that carry them run
+ * against mocked connections handed out by a driver of this test.
  */
 @Test(sequential = true)
 @SuppressWarnings("javadoc")
@@ -59,6 +89,35 @@
   private static final String ORACLE = "oracle.jdbc.driver.T4CConnection";
   private static final String POSTGRES = "org.postgresql.jdbc.PgConnection";
 
+  /** The tree every write of this test opens; the table name behind it is a hash of this name. */
+  private static final TreeName TREE = new TreeName("dc=example,dc=com", "id2entry");
+
+  private final StubDriver stub = new StubDriver();
+
+  /** Every test gets a pool of its own: the pools and the distrust of a pool are keyed by the url. */
+  private final AtomicInteger pools = new AtomicInteger();
+
+  /** The statement a create of a test runs, so that a test can assert that it ran - or that it did not. */
+  private PreparedStatement statements;
+
+  /** The connection behind the pool of a test, so that a test can assert the statement it was asked to prepare. */
+  private Connection engineConnection;
+
+  /**
+   * Connections whose class names carry the engine the way the drivers' own do - pgjdbc's
+   * {@code org.postgresql.jdbc.PgConnection}, Connector/J's {@code com.mysql.cj.jdbc.ConnectionImpl}. That name
+   * is what {@code driverNameOf()} matches an engine on, and the name of a mock is derived from the type it
+   * mocks, so a mock of plain {@link Connection} reaches no engine branch of {@code openTree()} at all. Lowercase
+   * because the match is case sensitive.
+   */
+  interface postgresConnection extends Connection
+  {
+  }
+
+  interface mysqlConnection extends Connection
+  {
+  }
+
   /** A failure whose cause chain is a cycle, to check that walking it terminates. */
   private static final class SelfCausedException extends RuntimeException
   {
@@ -205,6 +264,155 @@
     assertEquals(JDBCStorage.replayable(attempt, elapsedNanos, failure, driver), expected, name);
   }
 
+  @DataProvider
+  public Object[][] connectionFailures()
+  {
+    return new Object[][] {
+      // class 08, connection exception: pgjdbc reports the next use of a connection the server dropped as 08003,
+      // and a socket that failed under it as 08006, while a connect that never came up is 08001
+      { "connection does not exist", sql(0, "08003"), true },
+      { "connection failure", sql(0, "08006"), true },
+      { "unable to establish connection", sql(0, "08001"), true },
+      // the FATAL message a pg_terminate_backend or a shutdown sends before the socket closes: the connection is
+      // gone, and only its next use would be reported as class 08
+      { "admin shutdown", sql(0, "57P01"), true },
+      { "crash shutdown", sql(0, "57P02"), true },
+      { "cannot connect now", sql(0, "57P03"), true },
+      // it reaches write() wrapped, exactly as a conflict does
+      { "wrapped once", new StorageRuntimeException(sql(0, "08006")), true },
+      { "wrapped twice",
+        new DirectoryException(OTHER, raw("unchecked"), new StorageRuntimeException(sql(0, "08003"))), true },
+      { "wrapped 57P0x", new StorageRuntimeException(sql(0, "57P01")), true },
+      // the types the JDBC contract gives a driver to say the connection is gone, whatever state it fills in:
+      // oracle reports ORA-03113 and ORA-01089 as SQLRecoverableException, and only happens to map them to 08006
+      { "recoverable", new SQLRecoverableException("closed connection", "72000", 3113), true },
+      { "non transient connection", new SQLNonTransientConnectionException("socket closed", "S1000", 0), true },
+      // a driver reports what happened as the next exception of a generic failure as readily as it reports it
+      // as the cause, and mssql-jdbc chains every error of a message it received that way
+      { "next exception", chained(sql(0, "HY000"), sql(0, "08006")), true },
+      // the drop of the rollback that releases a connection arrives suppressed into the failure of the operation
+      { "suppressed", suppressing(sql(2627, "23000"), sql(0, "08006")), true },
+
+      // a statement the database answered, however badly, leaves the connection usable
+      { "deadlock victim", sql(1205, "40001"), false },
+      { "primary key violation", sql(2627, "23000"), false },
+      // 53300 is the server refusing a further connection, not the loss of one already established
+      { "too many connections", sql(0, "53300"), false },
+      // a killed session on SQL Server: generateStateCode maps neither 596 nor its siblings, so with xopenStates
+      // off - the default - it arrives as "S"+errorState and no state tells it from a rejected statement. What
+      // does tell it apart is the connection the driver closed behind it, see the test below
+      { "mssql killed session", sql(596, "S0001"), false },
+      { "no SQLState", sql(0, null), false },
+      { "not a SQLException", new IllegalStateException("connection closed"), false },
+      { "no failure at all", null, false },
+      { "cyclic cause chain", new SelfCausedException(), false },
+    };
+  }
+
+  @Test(dataProvider = "connectionFailures")
+  public void testIsConnectionFailure(String name, Throwable failure, boolean expected)
+  {
+    assertEquals(JDBCStorage.isConnectionFailure(failure), expected, name);
+  }
+
+  /**
+   * A connection the database dropped is replayed on a connection the next attempt borrows of its own - but only
+   * while the transaction has not been committed yet. A drop reported by {@code commit()} leaves the outcome of
+   * the transaction unknown, and replaying a write that in fact committed applies it twice.
+   */
+  @Test
+  public void testADroppedConnectionIsReplayedOnlyBeforeTheCommit()
+  {
+    final SQLException dropped = sql(0, "08006");
+    assertEquals(JDBCStorage.replayReason(dropped, POSTGRES, false, false, false),
+        "a connection the database dropped");
+    assertNull(JDBCStorage.replayReason(dropped, POSTGRES, true, false, false),
+        "an in doubt transaction was replayed");
+  }
+
+  /**
+   * A driver that closed the connection has said the connection is gone whatever SQLState it filled in - which is
+   * the only way a killed SQL Server session is ever recognized, since it arrives as S0001.
+   */
+  @Test
+  public void testAConnectionTheDriverClosedIsADroppedOne()
+  {
+    final SQLException killed = sql(596, "S0001");
+    assertNull(JDBCStorage.replayReason(killed, MSSQL, false, false, false), "S0001 was replayed on its own");
+    assertEquals(JDBCStorage.replayReason(killed, MSSQL, false, false, true),
+        "a connection the database dropped");
+    assertNull(JDBCStorage.replayReason(killed, MSSQL, true, false, true),
+        "an in doubt transaction was replayed");
+  }
+
+  /**
+   * An attempt that committed part of its own work is not replayed, whatever the failure says: what it did no
+   * longer rolls back as a whole, and a WriteOperation is only idempotent in the database. RootContainer.open
+   * opens and registers the entry containers of every base DN in one write, and a replay of it fails with
+   * ERR_ENTRY_CONTAINER_ALREADY_REGISTERED, masking the failure that caused the replay.
+   */
+  @Test
+  public void testAnAttemptThatCommittedPartOfItsWorkIsNotReplayed()
+  {
+    assertNull(JDBCStorage.replayReason(sql(0, "40001"), POSTGRES, false, true, false), "a conflict was replayed");
+    assertNull(JDBCStorage.replayReason(sql(0, "08006"), POSTGRES, false, true, false), "a drop was replayed");
+    assertNull(JDBCStorage.replayReason(sql(596, "S0001"), MSSQL, false, true, true), "a drop was replayed");
+  }
+
+  /**
+   * A conflict is replayed on the strength of the engine having rolled the transaction back before it answered,
+   * so it is read from the failure of the operation and not from the release of the connection: a class 40 the
+   * release contributed - Oracle reports a transaction rolled back under it as ORA-02091, SQLState 40000 - would
+   * otherwise re-authorise the replay of a commit whose outcome is unknown, past the guard that exists for it.
+   * A drop is read from the release as well, which is the one place it is often stated at all.
+   */
+  @Test
+  public void testAConflictIsNotReadFromTheReleaseOfTheConnection()
+  {
+    final SQLException onRelease = suppressing(sql(2627, "23000"), sql(0, "40000"));
+    assertFalse(JDBCStorage.isRetryableConflict(onRelease, POSTGRES), "a conflict was read from the release");
+    assertNull(JDBCStorage.replayReason(onRelease, POSTGRES, true, false, false),
+        "a transaction the commit left in doubt was replayed");
+
+    // the same shape carrying a drop instead: read, since the release is where a drop is stated at all
+    assertTrue(JDBCStorage.isConnectionFailure(suppressing(sql(2627, "23000"), sql(0, "08006"))),
+        "a drop was not read from the release");
+  }
+
+  /** The connection is asked only where a state does not already say the connection is gone. */
+  @Test
+  public void testTheConnectionIsAskedWhetherTheDriverClosedIt() throws Exception
+  {
+    final Connection closed = mock(Connection.class);
+    when(closed.isClosed()).thenReturn(true);
+    final Connection alive = mock(Connection.class);
+    when(alive.isClosed()).thenReturn(false);
+    final Connection mute = mock(Connection.class);
+    when(mute.isClosed()).thenThrow(new SQLException("the connection cannot say"));
+
+    assertTrue(JDBCStorage.isConnectionFailure(sql(596, "S0001"), closed), "a killed session was not recognized");
+    assertFalse(JDBCStorage.isConnectionFailure(sql(2627, "23000"), alive), "a rejected statement was a drop");
+    assertTrue(JDBCStorage.isConnectionFailure(sql(0, "08006"), alive), "class 08 needs no connection to say so");
+    assertTrue(JDBCStorage.isConnectionFailure(sql(2627, "23000"), mute), "a connection that cannot answer");
+  }
+
+  /** A conflict is a rollback the engine completed before it answered, whichever phase reported it. */
+  @Test
+  public void testAConflictIsReplayedFromEitherPhase()
+  {
+    final SQLException conflict = sql(0, "40001");
+    assertEquals(JDBCStorage.replayReason(conflict, POSTGRES, false, false, false), "a conflict");
+    assertEquals(JDBCStorage.replayReason(conflict, POSTGRES, true, false, false), "a conflict");
+  }
+
+  /** Everything else fails the operation, as it did before either replay existed. */
+  @Test
+  public void testAFailureOfTheStatementIsNotReplayed()
+  {
+    assertNull(JDBCStorage.replayReason(sql(2627, "23000"), MSSQL, false, false, false));
+    assertNull(JDBCStorage.replayReason(sql(2627, "23000"), MSSQL, true, false, false));
+  }
+
   /** The delay grows with the attempt, so that the replays outlast a contention lasting more than a few ms. */
   @Test
   public void testRetryDelayGrowsAndStaysBounded()
@@ -233,19 +441,545 @@
   public void testConflictSummaryNamesTheStateAndTheNumber()
   {
     final String summary = JDBCStorage.conflictSummary(
-        new DirectoryException(OTHER, raw("unchecked"), new StorageRuntimeException(sql(1205, "40001"))));
+        new DirectoryException(OTHER, raw("unchecked"), new StorageRuntimeException(sql(1205, "40001"))), POSTGRES);
     assertTrue(summary.contains("40001"), summary);
     assertTrue(summary.contains("1205"), summary);
     assertTrue(summary.contains("synthetic failure"), summary);
   }
 
+  /**
+   * That line is the only record a replay leaves, so it names the failure the replay was decided on. A write whose
+   * operation was rejected and whose release then reported a drop is replayed on the class 08 suppressed into the
+   * rejection, and naming the state of the rejected statement would describe a replay that did not happen.
+   */
+  @Test
+  public void testConflictSummaryNamesTheFailureTheReplayWasDecidedOn()
+  {
+    final String summary = JDBCStorage.conflictSummary(
+        new StorageRuntimeException(suppressing(sql(2627, "23000"), sql(0, "08006"))), POSTGRES);
+    assertTrue(summary.contains("08006"), summary);
+    assertFalse(summary.contains("23000"), summary);
+  }
+
   /** A failure carrying no SQLException at all, and a cyclic cause chain, still have to yield something loggable. */
   @Test
   public void testConflictSummaryTerminatesWithoutASQLException()
   {
-    assertTrue(JDBCStorage.conflictSummary(new IllegalStateException("connection closed")).contains("closed"));
-    assertTrue(JDBCStorage.conflictSummary(new SelfCausedException()).contains("SelfCausedException"));
-    assertEquals(JDBCStorage.conflictSummary(null), "null");
+    assertTrue(JDBCStorage.conflictSummary(new IllegalStateException("connection closed"), POSTGRES).contains("closed"));
+    assertTrue(JDBCStorage.conflictSummary(new SelfCausedException(), POSTGRES).contains("SelfCausedException"));
+    assertEquals(JDBCStorage.conflictSummary(null, POSTGRES), "null");
+  }
+
+  /** A statement that carries neither a conflict nor a drop is still the one the summary names. */
+  @Test
+  public void testConflictSummaryFallsBackToTheFirstFailureOfTheChain()
+  {
+    final String summary = JDBCStorage.conflictSummary(new StorageRuntimeException(sql(2627, "23000")), POSTGRES);
+    assertTrue(summary.contains("23000"), summary);
+
+    // the fallback names the statement, not the rollback of the release behind it: this is where a replay
+    // decided on the closed flag of the connection alone lands - neither chain carries a verdict of its own -
+    // and the walk reaches the suppressed exceptions of a failure before its cause
+    final StorageRuntimeException killedSession = new StorageRuntimeException(sql(596, "S0001"));
+    killedSession.addSuppressed(sql(0, "25P02"));
+    final String decidedOnTheConnection = JDBCStorage.conflictSummary(killedSession, MSSQL);
+    assertTrue(decidedOnTheConnection.contains("S0001"), decidedOnTheConnection);
+    assertFalse(decidedOnTheConnection.contains("25P02"), decidedOnTheConnection);
+  }
+
+  /**
+   * The walk of a failure looks at a bounded number of links: mssql-jdbc chains every error of one message it
+   * received through {@code setNextException}, and a budget spent on those would never reach the cause a wrapper
+   * carries. Pinned from both sides - a drop on the last link of the budget is found and one link further is not
+   * - since a number nothing pins drifts unnoticed in either direction.
+   */
+  @Test
+  public void testTheWalkOfAFailureStopsAtItsBudget()
+  {
+    assertTrue(JDBCStorage.isConnectionFailure(chainEndingInADrop(64)), "a drop on the last link of the budget");
+    assertFalse(JDBCStorage.isConnectionFailure(chainEndingInADrop(65)), "a drop past the budget was walked to");
+  }
+
+  /**
+   * Opening a tree that is already there commits nothing, so the attempt stays replayable. The create table is
+   * guarded by a catalog read, and so is the create index on every engine but postgresql, so on an existing
+   * backend {@code openTree(name, true)} issues no statement at all - while
+   * {@code RootContainer.open()} opens every tree of every base DN in a single write whose first act is one of
+   * these. A flag raised on the catalog read alone would leave that write unreplayable for the life of the
+   * backend, the conflict replay of #867 included: {@code replayReason()} reads the flag before anything else.
+   */
+  @Test
+  public void testOpeningAnExistingTreeLeavesTheAttemptReplayable() throws Exception
+  {
+    final JDBCStorage storage = storageOverACatalogHolding(true);
+    final AtomicInteger attempts = new AtomicInteger();
+
+    storage.write(txn -> {
+      txn.openTree(TREE, true);
+      if (attempts.incrementAndGet() == 1)
+      {
+        throw new StorageRuntimeException(sql(0, "40001"));
+      }
+    });
+
+    assertEquals(attempts.get(), 2, "a transaction that committed nothing was not replayed");
+    verify(statements, never()).executeUpdate();
+  }
+
+  /**
+   * A tree that had to be created did commit - the create table commits, and mysql and oracle commit before a DDL
+   * statement of their own accord - so the attempt is out of the replay whatever the failure says: a
+   * {@link WriteOperation} is only idempotent in the database, and {@code RootContainer.open()} replayed after the
+   * trees of the first base DN were created registers that base DN a second time.
+   */
+  @Test
+  public void testCreatingATreeTakesTheAttemptOutOfTheReplay() throws Exception
+  {
+    final JDBCStorage storage = storageOverACatalogHolding(false);
+    final AtomicInteger attempts = new AtomicInteger();
+
+    try
+    {
+      storage.write(txn -> {
+        txn.openTree(TREE, true);
+        attempts.incrementAndGet();
+        throw new StorageRuntimeException(sql(0, "40001"));
+      });
+      fail("a transaction that had committed a create table was replayed");
+    }
+    catch (StorageRuntimeException expected)
+    {
+      assertTrue(JDBCStorage.isRetryableConflict(expected, POSTGRES), "the conflict was not the failure raised");
+    }
+    assertEquals(attempts.get(), 1, "a transaction that committed part of its work was replayed");
+    verify(statements).executeUpdate();
+  }
+
+  /**
+   * The rollback that unwinds a failed attempt is often the first place a drop is stated outright, and on a
+   * driver that reports a killed session as a plain vendor error it is the only one. It is joined to the failure
+   * being unwound rather than dropped on the floor, so that the classifiers below read it: without it the attempt
+   * would lean on the driver having flipped its closed flag already, and a driver that has not gives neither the
+   * replay nor the distrust.
+   */
+  @Test
+  public void testTheRollbackOfAFailedAttemptIsNotSwallowed() throws Exception
+  {
+    final long window = CachedConnection.aliveBypassNanos;
+    CachedConnection.aliveBypassNanos = TimeUnit.HOURS.toNanos(1);
+    try
+    {
+      final Connection pooled = mock(Connection.class);
+      when(pooled.isValid(anyInt())).thenReturn(true);
+      final Connection dropped = mock(Connection.class);
+      when(dropped.isValid(anyInt())).thenReturn(true);
+      when(dropped.isClosed()).thenReturn(false); // the driver has not flipped its flag yet
+
+      final JDBCStorage storage = storageOver(pooled, dropped);
+      final Connection first = storage.getConnection();
+      final Connection second = storage.getConnection();
+      first.close();
+      second.close();
+      // proven alive by the connect itself, and inside the window ever since: nothing has validated
+      verify(dropped, never()).isValid(anyInt());
+
+      // only the rollback that unwinds the attempt says the connection is gone: the release behind it
+      // goes through, so the dropped connection is back at the head of the pool - where the replay
+      // borrows it again - with nothing else to report what it saw
+      doThrow(new SQLException("connection reset", "08006")).doNothing().when(dropped).rollback();
+
+      final AtomicInteger attempts = new AtomicInteger();
+      storage.write(txn -> {
+        if (attempts.incrementAndGet() == 1)
+        {
+          throw new StorageRuntimeException(sql(596, "S0001")); // a killed session, as mssql-jdbc reports it
+        }
+      });
+
+      assertEquals(attempts.get(), 2, "the drop the rollback reported was not replayed");
+      // the distrust reached the pool: the borrow of the replay validated instead of trusting the
+      // last answer of a connection that predates the drop
+      verify(dropped, times(1)).isValid(CachedConnection.VALIDATION_TIMEOUT_SECONDS);
+    }
+    finally
+    {
+      CachedConnection.aliveBypassNanos = window;
+    }
+  }
+
+  /**
+   * A drop the release of the connection reported reaches the pool as well as the replay. It is suppressed into
+   * the failure of the operation (JLS 14.20.3.1) rather than replacing it, so the attempt sees it only on the
+   * chains of that failure - and the pool has no other way of hearing of it: the rest of that generation would
+   * otherwise be handed out unvalidated one by one until the pool runs out of it.
+   */
+  @Test
+  public void testADropReportedByTheReleaseReachesThePool() throws Exception
+  {
+    final long window = CachedConnection.aliveBypassNanos;
+    CachedConnection.aliveBypassNanos = TimeUnit.HOURS.toNanos(1);
+    try
+    {
+      final Connection pooled = mock(Connection.class);
+      when(pooled.isValid(anyInt())).thenReturn(true);
+      final Connection released = mock(Connection.class);
+      when(released.isValid(anyInt())).thenReturn(true);
+
+      final JDBCStorage storage = storageOver(pooled, released);
+      // both are proven alive and back in the pool; the one released last is the one the write borrows
+      final Connection first = storage.getConnection();
+      final Connection second = storage.getConnection();
+      first.close();
+      second.close();
+
+      // from here the database has dropped the connection at the head of the pool: the operation is
+      // rejected for its own reasons, the rollback that unwinds the attempt goes through, and the release
+      // behind it is where the drop surfaces. Chained, so that the drop lands on the second rollback: an
+      // unchained stub fails the first one - the rollback of the attempt - and pins the sibling test above
+      doNothing().doThrow(new SQLException("connection reset", "08006")).when(released).rollback();
+
+      final AtomicInteger attempts = new AtomicInteger();
+      storage.write(txn -> {
+        if (attempts.incrementAndGet() == 1)
+        {
+          throw new StorageRuntimeException(sql(2627, "23000"));
+        }
+      });
+
+      assertEquals(attempts.get(), 2, "the drop suppressed into the failure was not replayed");
+      // the return to the pool that seeded it, the rollback of the attempt, and the release behind it - which
+      // is the one that reported, since the stub above lets the rollback of the attempt through
+      verify(released, times(3)).rollback();
+      // the distrust reached the pool from the release: the borrow of the replay validated instead of
+      // trusting the last answer of a connection established before the drop
+      verify(pooled).isValid(CachedConnection.VALIDATION_TIMEOUT_SECONDS);
+    }
+    finally
+    {
+      CachedConnection.aliveBypassNanos = window;
+    }
+  }
+
+  /**
+   * A read is never replayed - two of the read operations of this server are not idempotent - but a drop it ran
+   * into still has to reach the pool, which has no other way of hearing of one: a borrow inside the window asks
+   * the database nothing, so the statement that broke is the only place the drop is ever seen. The release of
+   * the connection counts as such a statement: its rollback is the one round trip a read that found nothing
+   * makes.
+   */
+  @Test
+  public void testADropAReadRanIntoReachesThePool() throws Exception
+  {
+    final long window = CachedConnection.aliveBypassNanos;
+    CachedConnection.aliveBypassNanos = TimeUnit.HOURS.toNanos(1);
+    try
+    {
+      final Connection pooled = mock(Connection.class);
+      when(pooled.isValid(anyInt())).thenReturn(true);
+      final Connection released = mock(Connection.class);
+      when(released.isValid(anyInt())).thenReturn(true);
+
+      final JDBCStorage storage = storageOver(pooled, released);
+      final Connection first = storage.getConnection();
+      final Connection second = storage.getConnection();
+      first.close();
+      second.close();
+      // both are proven alive and inside the window: nothing has validated
+      verify(released, never()).isValid(anyInt());
+
+      // the read is rejected for its own reasons, and the release behind it - a read issues no rollback of its
+      // own - is where the connection the database dropped says so
+      doThrow(new SQLException("connection reset", "08006")).when(released).rollback();
+      try
+      {
+        storage.read(txn -> {
+          throw new StorageRuntimeException(sql(2627, "23000"));
+        });
+        fail("the failure of the read was swallowed");
+      }
+      catch (StorageRuntimeException expected)
+      {
+        assertTrue(JDBCStorage.isConnectionFailure(expected), "the drop of the release did not reach the failure");
+      }
+
+      storage.getConnection().close(); // the borrow that follows it validates instead of trusting
+
+      verify(pooled).isValid(CachedConnection.VALIDATION_TIMEOUT_SECONDS);
+    }
+    finally
+    {
+      CachedConnection.aliveBypassNanos = window;
+    }
+  }
+
+  /**
+   * The create index of the postgres branch is asked of the catalog first, although postgresql has "create index
+   * if not exists": that statement commits whether it creates anything or not, and unguarded it would take every
+   * write that opens a tree out of the replay - {@code RootContainer.open()} and its ~25 trees per suffix
+   * included.
+   */
+  @Test
+  public void testThePostgresIndexIsAskedOfTheCatalogBeforeItIsCreated() throws Exception
+  {
+    final JDBCStorage storage = storageOverAnEngine(postgresConnection.class, true);
+    final AtomicInteger attempts = new AtomicInteger();
+
+    storage.write(txn -> {
+      txn.openTree(TREE, true);
+      if (attempts.incrementAndGet() == 1)
+      {
+        throw new StorageRuntimeException(sql(0, "40001"));
+      }
+    });
+
+    assertEquals(attempts.get(), 2, "a transaction that committed nothing was not replayed");
+    verify(statements, never()).executeUpdate();
+  }
+
+  /**
+   * postgresql runs DDL inside the transaction, so a create index the engine rolled back has committed nothing:
+   * {@code write()} rolls the attempt back whole and replays it. Raising the flag in front of the statement -
+   * which is what mysql and oracle need, since they commit before a DDL of their own accord - would turn a
+   * deadlock the engine itself undid into a hard failure of the open.
+   */
+  @Test
+  public void testACreateIndexPostgresRolledBackLeavesTheAttemptReplayable() throws Exception
+  {
+    final JDBCStorage storage = storageOverAnEngine(postgresConnection.class, false);
+    when(statements.executeUpdate()).thenThrow(sql(0, "40P01")).thenReturn(0);
+    final AtomicInteger attempts = new AtomicInteger();
+
+    storage.write(txn -> {
+      attempts.incrementAndGet();
+      txn.openTree(TREE, true);
+    });
+
+    assertEquals(attempts.get(), 2, "a create index the engine rolled back was not replayed");
+    verify(engineConnection, times(2)).prepareStatement(startsWith("create index if not exists k_"));
+  }
+
+  /**
+   * mysql commits before a DDL statement whether asked to or not, so a create index that failed there has
+   * committed everything the transaction did before it just as surely as one that succeeded: the attempt is out
+   * of the replay whatever the failure says.
+   */
+  @Test
+  public void testACreateIndexMysqlCommittedBeforeTakesTheAttemptOutOfTheReplay() throws Exception
+  {
+    final JDBCStorage storage = storageOverAnEngine(mysqlConnection.class, false);
+    when(statements.executeUpdate()).thenThrow(sql(1213, "40001"));
+    final AtomicInteger attempts = new AtomicInteger();
+
+    try
+    {
+      storage.write(txn -> {
+        attempts.incrementAndGet();
+        txn.openTree(TREE, true);
+      });
+      fail("a transaction whose create index had committed before it was replayed");
+    }
+    catch (StorageRuntimeException expected)
+    {
+      assertTrue(JDBCStorage.isRetryableConflict(expected, MYSQL), "the conflict was not the failure raised");
+    }
+    assertEquals(attempts.get(), 1, "an attempt that committed part of its work was replayed");
+    verify(engineConnection).prepareStatement(startsWith("create index k_"));
+  }
+
+  /**
+   * The connection the tree names are stamped on is closed as the attempt is unwound, and an unchecked throw out
+   * of a driver's {@code close()} there would replace the exception being unwound (JLS 14.20.2) - the very one
+   * the replay is decided on, and the only one that says what went wrong. The stamp is a diagnostic aid: it is
+   * joined to the failure instead, and the replay goes ahead.
+   */
+  @Test
+  public void testAFailingCommentConnectionDoesNotReplaceTheFailureOfTheWrite() throws Exception
+  {
+    final Connection stamp = mock(Connection.class);
+    when(stamp.createStatement()).thenReturn(mock(Statement.class)); // the lock bound of the stamp session
+    // the readback of the stored comment fails, so the stamp is given up on - with its connection open
+    when(stamp.prepareStatement(anyString())).thenThrow(new SQLException("no readback in this test", "42000"));
+    doThrow(new IllegalStateException("the driver threw out of close()")).when(stamp).close();
+    final JDBCStorage storage = storageOverAnEngine(postgresConnection.class, true, stamp);
+    final AtomicInteger attempts = new AtomicInteger();
+
+    storage.write(txn -> {
+      txn.openTree(TREE, true); // opens the stamp session, which is closed as this attempt is unwound
+      if (attempts.incrementAndGet() == 1)
+      {
+        throw new StorageRuntimeException(sql(0, "40001"));
+      }
+    });
+
+    assertEquals(attempts.get(), 2, "the failure of the comment connection replaced the conflict being unwound");
+    verify(stamp).close();
+  }
+
+  @BeforeClass
+  public void registerStubDriver() throws Exception
+  {
+    DriverManager.registerDriver(stub);
+  }
+
+  @AfterClass
+  public void deregisterStubDriver() throws Exception
+  {
+    DriverManager.deregisterDriver(stub);
+  }
+
+  /**
+   * A storage whose pool hands out one connection of this test, over a catalog that either holds the table of
+   * {@link #TREE} or does not. The connection is a mock of no recognized driver, which is how the engines that
+   * guard their create index - and mssql, which has none - reach {@code openTree}.
+   */
+  private JDBCStorage storageOverACatalogHolding(boolean theTable) throws Exception
+  {
+    final Connection con = mock(Connection.class);
+    final JDBCStorage storage = storageOver(con);
+
+    statements = mock(PreparedStatement.class);
+    final String tableName = storage.getTableName(TREE);
+    final DatabaseMetaData metaData = mock(DatabaseMetaData.class);
+    // a result set of its own per call: the catalog is asked once per attempt, and a replayed attempt
+    // reading a result set the previous one had already walked to its end would find no table there
+    when(metaData.getTables(any(), any(), any(), any())).thenAnswer(invocation -> {
+      final ResultSet tables = mock(ResultSet.class);
+      when(tables.next()).thenReturn(theTable, false);
+      when(tables.getString("TABLE_NAME")).thenReturn(tableName);
+      return tables;
+    });
+
+    when(con.isValid(anyInt())).thenReturn(true);
+    when(con.getMetaData()).thenReturn(metaData);
+    when(con.prepareStatement(anyString())).thenReturn(statements);
+    return storage;
+  }
+
+  /**
+   * A storage whose pool hands out one connection of the given engine, over a catalog holding the table of
+   * {@link #TREE} and either holding its {@code k_} index or not. The index guard and the statement behind it
+   * are the branches {@code openTree()} takes per engine, and a mock of plain {@link Connection} reaches none
+   * of them - so the name the mock ends up with is asserted here rather than assumed.
+   */
+  private JDBCStorage storageOverAnEngine(Class<? extends Connection> engine, boolean theIndex,
+      Connection... behind) throws Exception
+  {
+    final Connection con = mock(engine);
+    final String engineName = engine.getSimpleName().replace("Connection", "");
+    assertTrue(JDBCStorage.driverNameOf(con).contains(engineName),
+        "a mock of " + engine.getSimpleName() + " reaches no " + engineName + " branch: "
+            + JDBCStorage.driverNameOf(con));
+    engineConnection = con;
+    // the connections behind it answer the connects the pool does not make: the stamp of a tree name opens one
+    // of its own, straight through the driver, since the caller of openTree() is holding a pooled connection
+    final Connection[] answers = new Connection[behind.length + 1];
+    answers[0] = con;
+    System.arraycopy(behind, 0, answers, 1, behind.length);
+    final JDBCStorage storage = storageOver(answers);
+
+    statements = mock(PreparedStatement.class);
+    final String tableName = storage.getTableName(TREE);
+    final DatabaseMetaData metaData = mock(DatabaseMetaData.class);
+    // a result set of its own per call, for the reason the catalog of the test above hands out one: a replayed
+    // attempt reading a result set the previous one had already walked to its end would find nothing there
+    when(metaData.getTables(any(), any(), any(), any())).thenAnswer(invocation -> {
+      final ResultSet tables = mock(ResultSet.class);
+      when(tables.next()).thenReturn(true, false);
+      when(tables.getString("TABLE_NAME")).thenReturn(tableName);
+      return tables;
+    });
+    when(metaData.getIndexInfo(any(), any(), any(), anyBoolean(), anyBoolean())).thenAnswer(invocation -> {
+      final ResultSet indexes = mock(ResultSet.class);
+      when(indexes.next()).thenReturn(theIndex, false);
+      when(indexes.getString("INDEX_NAME")).thenReturn("k_" + tableName.substring("opendj_".length()));
+      return indexes;
+    });
+
+    when(con.isValid(anyInt())).thenReturn(true);
+    when(con.getMetaData()).thenReturn(metaData);
+    when(con.prepareStatement(anyString())).thenReturn(statements);
+    // the tree name the sweep stamps the table with runs on a connection of its own and is a diagnostic aid: a
+    // failure of it only logs, and this fixture is about the index statement rather than about the comment
+    when(con.createStatement()).thenThrow(new SQLException("no session statement in this test", "42000"));
+    return storage;
+  }
+
+  /**
+   * A storage of a pool of its own, which connects to the given connections in turn and answers every connect
+   * beyond them with the last. Every test gets a url of its own: both the pools and the distrust of a pool are
+   * keyed by the connection string, so a shared one would carry the state of one test into the next.
+   */
+  private JDBCStorage storageOver(Connection... connections) throws Exception
+  {
+    final JDBCBackendCfg cfg = mock(JDBCBackendCfg.class);
+    when(cfg.getDBDirectory()).thenReturn(StubDriver.PREFIX + pools.incrementAndGet());
+    final JDBCStorage storage = new JDBCStorage(cfg, null);
+    storage.accessMode = AccessMode.READ_WRITE;
+    stub.answerWith(connections);
+    return storage;
+  }
+
+  /** A driver of this test, so that the pool the write borrows from needs no database behind it. */
+  private static final class StubDriver implements Driver
+  {
+    static final String PREFIX = "jdbc:opendj-retry-stub:";
+
+    private volatile Connection[] answers = new Connection[0];
+    private final AtomicInteger connects = new AtomicInteger();
+
+    void answerWith(Connection... answers)
+    {
+      this.answers = answers;
+      this.connects.set(0);
+    }
+
+    @Override
+    public Connection connect(String url, Properties info)
+    {
+      if (!acceptsURL(url) || answers.length == 0)
+      {
+        return null;
+      }
+      // the last one answers every connect beyond the ones named, so a pool that opens more than the
+      // test set up gets a working connection rather than a null the driver contract reads as "not mine"
+      return answers[Math.min(connects.getAndIncrement(), answers.length - 1)];
+    }
+
+    @Override
+    public boolean acceptsURL(String url)
+    {
+      return url != null && url.startsWith(PREFIX);
+    }
+
+    @Override
+    public DriverPropertyInfo[] getPropertyInfo(String url, Properties info)
+    {
+      return new DriverPropertyInfo[0];
+    }
+
+    @Override
+    public int getMajorVersion()
+    {
+      return 1;
+    }
+
+    @Override
+    public int getMinorVersion()
+    {
+      return 0;
+    }
+
+    @Override
+    public boolean jdbcCompliant()
+    {
+      return false;
+    }
+
+    @Override
+    public Logger getParentLogger()
+    {
+      return Logger.getLogger(StubDriver.class.getName());
+    }
   }
 
   private static SQLException sql(int errorCode, String sqlState)
@@ -339,4 +1073,30 @@
     // halve the effective step and change the run without either row saying so
     assertEquals(clockReads.get(), expectedClockReads, name + ": clock reads");
   }
+
+  /** The second failure as the next exception of the first, the way a driver chains the errors of one message. */
+  private static SQLException chained(SQLException first, SQLException next)
+  {
+    first.setNextException(next);
+    return first;
+  }
+
+  /** A chain of the given number of next exceptions whose last link is a connection that broke. */
+  private static SQLException chainEndingInADrop(int links)
+  {
+    final SQLException head = sql(2627, "23000");
+    SQLException tail = head;
+    for (int link = 2; link <= links; link++)
+    {
+      tail = chained(tail, sql(0, link == links ? "08006" : "23000")).getNextException();
+    }
+    return head;
+  }
+
+  /** The second failure suppressed into the first, the way a failing close() joins the failure of an operation. */
+  private static SQLException suppressing(SQLException failure, SQLException onRelease)
+  {
+    failure.addSuppressed(onRelease);
+    return failure;
+  }
 }
diff --git a/opendj-server-legacy/src/test/java/org/opends/server/backends/jdbc/StampConnectionTestCase.java b/opendj-server-legacy/src/test/java/org/opends/server/backends/jdbc/StampConnectionTestCase.java
index 05b055e..25c5c14 100644
--- a/opendj-server-legacy/src/test/java/org/opends/server/backends/jdbc/StampConnectionTestCase.java
+++ b/opendj-server-legacy/src/test/java/org/opends/server/backends/jdbc/StampConnectionTestCase.java
@@ -214,12 +214,13 @@
 
 	/**
 	 * A driver reports the vendor error of a failed statement as the next exception of a generic
-	 * one at least as often as it reports it as the cause. Reading only the cause chain classifies
-	 * a lock timeout as a rejection, which leaves the tree unstamped until the next start over a
-	 * moment of contention.
+	 * one at least as often as it reports it as the cause, and the statement of a try-with-resources
+	 * carries what its {@code close()} saw as a suppressed exception. Reading fewer chains than the
+	 * classifiers of a write read classifies a lock timeout - or a connection that broke - as a
+	 * rejection, which leaves the tree unstamped for the life of the backend.
 	 */
 	@Test
-	public void testFailureScopeWalksBothChains() {
+	public void testFailureScopeWalksEveryChain() {
 		final SQLException reportedAsTheCause = new SQLException("statement failed",
 			new SQLException("lock wait timeout exceeded", "HY000", 1205));
 		assertEquals(JDBCStorage.failureScope(reportedAsTheCause, JDBCStorage.Dialect.MYSQL),
@@ -236,6 +237,13 @@
 		assertEquals(JDBCStorage.failureScope(connectionGone, JDBCStorage.Dialect.MYSQL),
 			JDBCStorage.FailureScope.SESSION, "a connection exception on the next-exception chain was missed");
 
+		// the close() of the statement is where a connection that broke under a stamp is often the
+		// only witness, and it joins the failure being unwound as a suppressed exception (JLS 14.20.3.1)
+		final SQLException reportedByTheClose = new SQLException("statement failed");
+		reportedByTheClose.addSuppressed(new SQLException("connection closed", "08006"));
+		assertEquals(JDBCStorage.failureScope(reportedByTheClose, JDBCStorage.Dialect.MYSQL),
+			JDBCStorage.FailureScope.SESSION, "a connection exception suppressed into the failure was missed");
+
 		// a driver that chains an exception back to itself must not make the walk loop
 		final SQLException selfReferring = new SQLException("statement failed");
 		selfReferring.setNextException(selfReferring);
diff --git a/opendj-server-legacy/src/test/java/org/opends/server/backends/jdbc/TestCase.java b/opendj-server-legacy/src/test/java/org/opends/server/backends/jdbc/TestCase.java
index b650301..22e8ea1 100644
--- a/opendj-server-legacy/src/test/java/org/opends/server/backends/jdbc/TestCase.java
+++ b/opendj-server-legacy/src/test/java/org/opends/server/backends/jdbc/TestCase.java
@@ -22,6 +22,7 @@
 import org.opends.server.backends.pluggable.spi.AccessMode;
 import org.opends.server.backends.pluggable.spi.Cursor;
 import org.opends.server.backends.pluggable.spi.Importer;
+import org.opends.server.backends.pluggable.spi.ReadOnlyStorageException;
 import org.opends.server.backends.pluggable.spi.ReadOperation;
 import org.opends.server.backends.pluggable.spi.ReadableTransaction;
 import org.opends.server.backends.pluggable.spi.TreeName;
@@ -45,6 +46,7 @@
 import java.util.Collections;
 import java.util.List;
 import java.util.NoSuchElementException;
+import java.util.Properties;
 import java.util.concurrent.Callable;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
@@ -56,6 +58,7 @@
 import static org.testng.Assert.assertEquals;
 import static org.testng.Assert.assertFalse;
 import static org.testng.Assert.assertNotEquals;
+import static org.testng.Assert.assertNotNull;
 import static org.testng.Assert.assertNull;
 import static org.testng.Assert.assertTrue;
 import static org.testng.Assert.fail;
@@ -140,6 +143,40 @@
 
 	protected abstract String getJdbcUrl();
 
+	/**
+	 * The second property bounding a login is a socket read timeout on mysql, oracle and sql
+	 * server: in force for the whole life of the connection it would fail every statement slower
+	 * than it - an import batch, the statistics of a freshly loaded table - so it has to be lifted
+	 * as soon as the login is through (#872).
+	 */
+	@Test(timeOut = 120000)
+	public void testLoginBoundDoesNotOutliveTheLogin() throws Exception {
+		final String url = createBackendCfg().getDBDirectory();
+		final CachedConnection.ConnectDialect dialect = CachedConnection.ConnectDialect.of(url);
+		assertNotNull(dialect, "the dialect of the container is one this backend bounds: " + CachedConnection.safeUrl(url));
+		System.setProperty(CachedConnection.CONNECT_TIMEOUT_PROPERTY, "2");
+		try {
+			// the bound this lifts has to be in force first, or the assertion below holds of a
+			// connection that never carried one: established here with the very properties the
+			// borrow uses, and read back off the socket of this driver
+			final Properties bounding = new Properties();
+			assertTrue(dialect.bound(url, bounding, 2),
+				"the read bound of the login is not set for this dialect, so there is nothing to lift");
+			try (final Connection bounded = DriverManager.getConnection(url, bounding)) {
+				assertEquals(bounded.getNetworkTimeout(), 2000,
+					"the property this dialect names does not bound the socket of its login");
+			}
+
+			// a pooled connection would be handed back without being established again
+			CachedConnection.cached.invalidate(url);
+			try (final Connection con = CachedConnection.getConnection(url)) {
+				assertEquals(con.getNetworkTimeout(), 0, "the read bound of the login is still in force");
+			}
+		} finally {
+			System.clearProperty(CachedConnection.CONNECT_TIMEOUT_PROPERTY);
+		}
+	}
+
 	private static ByteString key(int i) {
 		return ByteString.valueOfUtf8(String.format("key%02d", i));
 	}
@@ -284,6 +321,86 @@
 		}
 	}
 
+	/**
+	 * A storage opened READ_ONLY must still hand out the write transaction {@code RootContainer.open()} asks for
+	 * there - otherwise the offline export-ldif, verify-index and backendstat fail before reading anything - and
+	 * that transaction must serve exactly what the open needs and nothing more: opening an existing tree, reads,
+	 * cursors and record counts, while every mutation, including a delete through a cursor it opened, is
+	 * refused (#874).
+	 */
+	@Test
+	public void testReadOnlyTransactionReadsButRefusesWrites() throws Exception {
+		final JDBCStorage storage = new JDBCStorage(createBackendCfg(), null);
+		final TreeName tree = new TreeName("testReadOnlyTransaction", "tree");
+		final TreeName absent = new TreeName("testReadOnlyTransaction", "absent");
+		try {
+			storage.open(AccessMode.READ_WRITE);
+			storage.write(new WriteOperation() {
+				@Override
+				public void run(WriteableTransaction txn) throws Exception {
+					txn.openTree(tree, true);
+					txn.put(tree, key(0), value(0));
+					txn.put(tree, key(1), value(1));
+				}
+			});
+			storage.close();
+
+			storage.open(AccessMode.READ_ONLY);
+			storage.write(new WriteOperation() {
+				@Override
+				public void run(WriteableTransaction txn) throws Exception {
+					// what RootContainer.open() does through this transaction in read-only mode
+					txn.openTree(tree, false);
+					assertEquals(txn.read(tree, key(0)), value(0));
+					assertEquals(txn.getRecordCount(tree), 2);
+					try (final Cursor<ByteString, ByteString> cursor = txn.openCursor(tree)) {
+						assertTrue(cursor.next());
+						assertEquals(cursor.getKey(), key(0));
+						try {
+							cursor.delete();
+							fail("delete() through a cursor of a read-only transaction must fail");
+						} catch (UnsupportedOperationException expected) {}
+					}
+
+					assertReadOnly("openTree(createOnDemand)", () -> txn.openTree(absent, true));
+					assertReadOnly("put", () -> txn.put(tree, key(2), value(2)));
+					assertReadOnly("update", () -> txn.update(tree, key(0), old -> value(3)));
+					assertReadOnly("delete", () -> txn.delete(tree, key(0)));
+					assertReadOnly("deleteTree", () -> txn.deleteTree(tree));
+				}
+			});
+
+			// nothing above reached the database
+			storage.close();
+			storage.open(AccessMode.READ_WRITE);
+			storage.read(new ReadOperation<Void>() {
+				@Override
+				public Void run(ReadableTransaction txn) throws Exception {
+					assertEquals(txn.getRecordCount(tree), 2);
+					assertEquals(txn.read(tree, key(0)), value(0));
+					return null;
+				}
+			});
+		} finally {
+			try {
+				storage.write(new WriteOperation() {
+					@Override
+					public void run(WriteableTransaction txn) throws Exception {
+						txn.deleteTree(tree);
+					}
+				});
+			} catch (Exception ignored) {}
+			storage.close();
+		}
+	}
+
+	private static void assertReadOnly(String operation, Runnable mutation) {
+		try {
+			mutation.run();
+			fail(operation + " must fail on a read-only storage");
+		} catch (ReadOnlyStorageException expected) {}
+	}
+
 	/** Buffer-served repositioning relies on the database collating keys in unsigned byte order. */
 	@Test
 	public void testCursorKeyOrderIsUnsigned() throws Exception {
diff --git a/opendj-server-legacy/src/test/java/org/opends/server/backends/pluggable/PluggableBackendImplTestCase.java b/opendj-server-legacy/src/test/java/org/opends/server/backends/pluggable/PluggableBackendImplTestCase.java
index eef3190..6706f7b 100644
--- a/opendj-server-legacy/src/test/java/org/opends/server/backends/pluggable/PluggableBackendImplTestCase.java
+++ b/opendj-server-legacy/src/test/java/org/opends/server/backends/pluggable/PluggableBackendImplTestCase.java
@@ -1251,6 +1251,40 @@
     }
   }
 
+  /**
+   * export-ldif, verify-index and backendstat open a root container of their own, in READ_ONLY mode, when the
+   * backend is not already open - a stopped server or a disabled backend. RootContainer.open() asks the storage
+   * for a write transaction even in that mode, since that is where it opens the compressed schema and the entry
+   * containers, so a storage refusing to hand one out fails the three tools before they read anything (#874).
+   * <p>
+   * testReadOnly() above does not cover this: it expects a ReadOnlyStorageException and a storage that fails the
+   * open throws one too, from RootContainer.open() rather than from the write it is meant to be checking.
+   */
+  @Test
+  public void testOfflineToolsOpenBackendReadOnly() throws Exception
+  {
+    // Put the backend offline, so that the tools open a read-only root container of their own
+    backend.finalizeBackend();
+    try
+    {
+      final ByteArrayOutputStream exported = new ByteArrayOutputStream();
+      try (final LDIFExportConfig exportConfig = new LDIFExportConfig(exported))
+      {
+        backend.exportLDIF(exportConfig);
+      }
+      assertThat(exported.toString(StandardCharsets.UTF_8.name())).contains(testBaseDN.toString());
+
+      final VerifyConfig verifyConfig = new VerifyConfig();
+      verifyConfig.setBaseDN(testBaseDN);
+      verifyConfig.addCompleteIndex("dn2id");
+      assertThat(backend.verifyBackend(verifyConfig)).isEqualTo(0);
+    }
+    finally
+    {
+      backend.openBackend();
+    }
+  }
+
   @Test
   public void test_issue_496() throws Exception {
     int resultCode = TestCaseUtils.applyModifications(true,

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