external-software/github_OpenIdentityPlatform_OpenDJ.git

			@@ -42,6 +42,7 @@
			import java.util.NoSuchElementException;
			import java.util.Objects;
			import java.util.Set;
			import java.util.concurrent.TimeUnit;

			import org.forgerock.i18n.LocalizableMessage;
			import org.forgerock.i18n.slf4j.LocalizedLogger;
			@@ -101,7 +102,37 @@
			{
			private static final int IMPORT_DB_CACHE_SIZE = 32 * MB;

			private static final double MAX_SLEEP_ON_RETRY_MS = 50.0;
			/**
			* Number of attempts a {@link WriteableStorageImpl#write} makes before it propagates the conflict to the caller.
			* <p>
			* It is a budget of attempts and not of time, so it is only ever reached by the conflicts that report quickly.
			* PersistIt reports a write-write conflict only once it has waited on it, up to
			* {@code SharedResource.DEFAULT_MAX_WAIT_TIME} - a minute, which this backend never lowers - so a conflict slower
			* to report than {@link #MAX_RETRY_WINDOW_NANOS} spends the whole window inside its first attempt, is granted the
			* single replay that window's exemption guarantees, and gives up on the window after two attempts rather than
			* after this many.
			*/
			static final int MAX_RETRIES = 10;

			/**
			* Wall-clock budget the replays of a {@link WriteableStorageImpl#write} may spend, in nanoseconds. It is checked
			* between attempts, so an attempt already running is never interrupted, and never before one replay has been
			* made: the loop returns after at most this window plus two attempts. It bounds the conflicts that are slow to
			* report, which {@link #MAX_RETRIES} alone does not - an operation whose own work takes seconds would otherwise
			* multiply that wait by the attempt count.
			*/
			static final long MAX_RETRY_WINDOW_NANOS = 10L * 1000L * 1000L * 1000L; //10 s

			/**
			* Upper bound of the random delay before the second attempt, in milliseconds; it doubles with every attempt. This
			* is the bound of the flat sleep this loop took before it was bounded, so the first replay is delayed exactly as
			* it was and only the later ones back off.
			*/
			private static final double BASE_SLEEP_ON_RETRY_MS = 50.0;

			/** Upper bound the doubled delay is capped at, in milliseconds. */
			private static final double MAX_SLEEP_ON_RETRY_MS = 1000.0;

			private static final String VOLUME_NAME = "dj";
			private static final String JOURNAL_NAME = VOLUME_NAME + "_journal";
			/** The buffer / page size used by the PersistIt storage. */
			@@ -635,8 +666,11 @@
			public void write(WriteOperation operation) throws Exception
			{
			final Transaction txn = db.getTransaction();
			for (;;)
			final long startedAt = System.nanoTime();
			final long giveUpAt = startedAt + retryWindowNanos;
			for (int attempt = 1;; attempt++)
			{
			final RollbackException conflict;
			txn.begin();
			try
			{
			@@ -653,8 +687,7 @@
			}
			catch (final RollbackException e)
			{
			// retry after random sleep (reduces transactions collision. Drawback: increased latency)
			Thread.sleep((long) (Math.random() * MAX_SLEEP_ON_RETRY_MS));
			conflict = e;
			}
			catch (final Exception e)
			{
			@@ -665,6 +698,68 @@
			{
			txn.end();
			}
			// decided and slept for outside the try statement: the sleep used to run before the finally ended the
			// rolled back transaction, holding it open for the whole backoff and lengthening the window every other
			// writer collides with
			//System.nanoTime() - giveUpAt is the overflow safe form of the comparison, and attempt > 1 keeps the
			//window from ending the loop before a single replay: persistit reports a write-write conflict only once
			//it has waited on it, up to SharedResource.DEFAULT_MAX_WAIT_TIME - a minute, which this backend never
			//lowers - so one attempt can outlast the window on its own, and it is the attempt after that one which
			//is likeliest to succeed, the transaction that blocked it having just finished
			//one clock sample for both, so that the elapsed time reported is the one the give up was decided on
			final long now = System.nanoTime();
			final boolean capSpent = attempt >= maxRetries;
			if (capSpent \|\| (attempt > 1 && now - giveUpAt >= 0))
			{
			final long elapsedMs = TimeUnit.NANOSECONDS.toMillis(now - startedAt);
			//which of the two bounds was spent, so that the config change paths - which report this as a bare stack
			//trace with no message id - say whether raising the attempts or the window is what would have helped
			final String boundSpent = capSpent ? "attempt cap" : "retry window";
			final StorageRuntimeException spent = new StorageRuntimeException(
			"pdb: backend '" + config.getBackendId() + "' did not apply the transaction after " + attempt
			+ " attempts in " + elapsedMs + " ms, the " + boundSpent + " being spent; the last conflict was "
			+ conflict);
			// the conflict is suppressed rather than made the cause, because a cause is what every caller strips
			// this message off with: write(WriteOperation) below unwraps a StorageRuntimeException that carries one
			// and throws the cause in its place, and EntryContainer.throwAllowedExceptionTypes:1121 rethrows a
			// StorageRuntimeException unchanged only while getCause() is null, wrapping it a second time otherwise.
			// Either way the caller would be left holding a bare RollbackException, whose StorageRuntimeException
			// message is only its class name - which is all ERR_OPEN_ENV_FAIL would then print at startup
			spent.addSuppressed(conflict);
			//warned once, at exhaustion only, unlike JDBCStorage which warns on every replay: a conflict is routine
			//on the ordinary add and modify path of this engine and a line per replay would flood the log. It names
			//the bound that was spent for the same reason the exception does, and it is the only rendering that can
			//carry the stack of the conflict: stackTraceToSingleLineString, the form the config change paths report
			//this exception with, walks the causes and never prints a suppressed exception
			logger.warn(LocalizableMessage.raw("pdb: giving up on the transaction of backend '%s' after %d attempts"
			+ " in %d ms, the %s being spent: %s", config.getBackendId(), attempt, elapsedMs, boundSpent,
			stackTraceToSingleLineString(conflict)));
			throw spent;
			}
			if (logger.isTraceEnabled())
			{
			logger.trace("pdb: replaying the transaction after %s, attempt %d of %d", conflict, attempt, maxRetries);
			}
			try
			{
			// retry after random sleep (reduces transactions collision. Drawback: increased latency), growing with
			// every attempt so that a contention the first delays did not outlast still has a chance to clear
			Thread.sleep(retryDelayMillis(attempt));
			}
			catch (final InterruptedException e)
			{
			//sleep cleared the interrupt flag: restore it, and report the conflict being replayed rather than the
			//interrupt, which would hide from the caller what actually went wrong. Wrapped the way the exhausted
			//loop above wraps it, and for the same reason: a RollbackException carries no message of its own, so
			//every caller that wraps one reports nothing but its class name
			Thread.currentThread().interrupt();
			final StorageRuntimeException interrupted = new StorageRuntimeException(
			"pdb: backend '" + config.getBackendId() + "' was interrupted while replaying the transaction after "
			+ attempt + " attempts; the last conflict was " + conflict);
			interrupted.addSuppressed(conflict);
			interrupted.addSuppressed(e);
			throw interrupted;
			}
			}
			}
			}
			@@ -915,6 +1010,10 @@
			private PDBMonitor monitor;
			private MemoryQuota memQuota;
			private StorageStatus storageStatus = StorageStatus.working();
			/** Attempt bound of a {@link WriteableStorageImpl#write}, {@link #MAX_RETRIES} outside the tests. */
			private final int maxRetries;
			/** Wall-clock bound of a {@link WriteableStorageImpl#write}, {@link #MAX_RETRY_WINDOW_NANOS} outside the tests. */
			private final long retryWindowNanos;

			/**
			* Creates a new persistit storage with the provided configuration.
			@@ -928,7 +1027,34 @@
			// FIXME: should be package private once importer is decoupled.
			public PDBStorage(final PDBBackendCfg cfg, ServerContext serverContext) throws ConfigException
			{
			this(cfg, serverContext, MAX_RETRIES, MAX_RETRY_WINDOW_NANOS);
			}

			/**
			* Creates a new persistit storage whose replay bounds are the given ones rather than {@link #MAX_RETRIES} and
			* {@link #MAX_RETRY_WINDOW_NANOS}.
			* <p>
			* Only a test builds one of these, and it does so to stop the two bounds racing each other: with the shipped
			* values a run of replays spends a random share of the window on backoff alone, so a test of the attempt cap
			* can be ended by the window on a loaded machine, and a test of the window has to spend seconds of build time
			* to reach it.
			*
			* @param cfg
			* The configuration.
			* @param serverContext
			* This server instance context
			* @param maxRetries
			* Number of attempts a write makes before it propagates the conflict to the caller.
			* @param retryWindowNanos
			* Wall-clock budget the replays of a write may spend, in nanoseconds.
			* @throws ConfigException if memory cannot be reserved
			*/
			PDBStorage(final PDBBackendCfg cfg, ServerContext serverContext, int maxRetries, long retryWindowNanos)
			throws ConfigException
			{
			this.serverContext = serverContext;
			this.maxRetries = maxRetries;
			this.retryWindowNanos = retryWindowNanos;
			backendDirectory = getBackendDirectory(cfg);
			config = cfg;
			cfg.addPDBChangeListener(this);
			@@ -1095,6 +1221,24 @@
			return new ImporterImpl();
			}

			/**
			* {@inheritDoc}
			* <p>
			* A transaction the engine rolled back is replayed, bounded twice: by {@link #MAX_RETRIES} attempts and by the
			* {@link #MAX_RETRY_WINDOW_NANOS} wall-clock window, whichever is spent first - except that the window alone
			* never ends the replays before one has been made. It is bounded because the
			* configuration change paths of the pluggable backend hold an entry container's exclusive lock across this
			* method, and every reader of that suffix then waits - untimed and uninterruptibly - until it returns, so a
			* conflict that never clears would park every worker thread of that suffix rather than fail one operation.
			* <p>
			* Once the bound is spent the conflict is reported as a {@link StorageRuntimeException} naming the backend, the
			* attempts spent, the time they took and which of the two bounds ran out. It carries the conflict as a
			* suppressed exception rather than as its cause: a cause is unwrapped below and thrown in its place, and
			* {@code EntryContainer.throwAllowedExceptionTypes} likewise passes a {@link StorageRuntimeException} through
			* untouched only while it has no cause. Given a cause, both hand the caller a bare RollbackException instead,
			* and the message of a {@link StorageRuntimeException} wrapping one is just its class name - which is all
			* {@code ERR_OPEN_ENV_FAIL} would report when this happens as a backend starts.
			*/
			@Override
			public void write(final WriteOperation operation) throws Exception
			{
			@@ -1108,6 +1252,14 @@
			}
			}

			/** Returns the randomized delay before the given attempt is replayed, doubling with each attempt up to a cap. */
			//package private like the JDBCStorage copy it is taken from, so that a test can pin the growth and the 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)));
			return (long) (Math.random() * bound);
			}

			private Exception unwrap(StorageRuntimeException e) throws Exception
			{
			if (e.getCause() != null)