/*
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* CDDL HEADER START
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*
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* The contents of this file are subject to the terms of the
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* Common Development and Distribution License, Version 1.0 only
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* (the "License"). You may not use this file except in compliance
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* with the License.
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*
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* You can obtain a copy of the license at legal-notices/CDDLv1_0.txt
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* or http://forgerock.org/license/CDDLv1.0.html.
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* See the License for the specific language governing permissions
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* and limitations under the License.
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*
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* When distributing Covered Code, include this CDDL HEADER in each
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* file and include the License file at legal-notices/CDDLv1_0.txt.
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* If applicable, add the following below this CDDL HEADER, with the
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* fields enclosed by brackets "[]" replaced with your own identifying
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* information:
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* Portions Copyright [yyyy] [name of copyright owner]
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*
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* CDDL HEADER END
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*
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*
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* Copyright 2013-2015 ForgeRock AS
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*/
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package org.opends.server.replication.server.changelog.api;
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import java.io.Closeable;
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/**
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* Generic cursor interface into the changelog database. Once it is not used
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* anymore, a cursor must be closed to release all the resources into the
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* database.
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* <p>
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* The cursor provides a java.sql.ResultSet like API : it is positioned before
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* the first requested record and needs to be moved forward by calling
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* {@link DBCursor#next()}.
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* <p>
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* Usage:
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* <pre>
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* {@code
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* DBCursor cursor = ...;
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* try {
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* while (cursor.next()) {
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* Record record = cursor.getRecord();
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* // ... can call cursor.getRecord() again: it will return the same result
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* }
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* }
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* finally {
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* close(cursor);
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* }
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* }
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* </pre>
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*
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* A cursor can be initialised from a key, using a {@code KeyMatchingStrategy} and
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* a {@code PositionStrategy}, to determine the exact starting position.
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* <p>
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* Let's call Kp the highest key lower than K and Kn the lowest key higher
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* than K : Kp < K < Kn
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* <ul>
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* <li>When using EQUAL_TO_KEY on key K :
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* <ul>
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* <li>with ON_MATCHING_KEY, cursor is positioned on key K (if K exists in log),
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* otherwise it is empty</li>
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* <li>with AFTER_MATCHING_KEY, cursor is positioned on key Kn (if K exists in log),
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* otherwise it is empty</li>
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* </ul>
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* </li>
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* <li>When using LESS_THAN_OR_EQUAL_TO_KEY on key K :
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* <ul>
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* <li>with ON_MATCHING_KEY, cursor is positioned on key K (if K exists in log)
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* or else Kp (if Kp exists in log), otherwise it is empty</li>
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* <li>with AFTER_MATCHING_KEY, cursor is positioned on key Kn (if Kp or K exist in log),
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* otherwise it is empty</li>
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* </ul>
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* </li>
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* <li>When using GREATER_THAN_OR_EQUAL_TO_KEY on key K :
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* <ul>
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* <li>with ON_MATCHING_KEY, cursor is positioned on key K (if K exists in log)
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* or else Kn (if Kn exists in log), otherwise it is empty</li>
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* <li>with AFTER_MATCHING_KEY, cursor is positioned on key Kn (if K or Kn exist in log),
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* otherwise it is empty</li>
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* </ul>
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* </li>
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* </ul>
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*
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* @param <T>
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* type of the record being returned
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* \@NotThreadSafe
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*/
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public interface DBCursor<T> extends Closeable
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{
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/**
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* Represents a cursor key matching strategy, which allow to choose if only
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* the exact key must be found or if any key equal or lower/higher should match.
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*/
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public enum KeyMatchingStrategy {
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/** Matches if the key or a lower key is found. */
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LESS_THAN_OR_EQUAL_TO_KEY,
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/** Matches only if the exact key is found. */
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EQUAL_TO_KEY,
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/** Matches if the key or a greater key is found. */
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GREATER_THAN_OR_EQUAL_TO_KEY
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}
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/**
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* Represents a cursor positioning strategy, which allow to choose if the start point
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* corresponds to the record at the provided key or the record just after the provided
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* key.
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*/
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public enum PositionStrategy {
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/** Start point is on the matching key. */
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ON_MATCHING_KEY,
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/** Start point is after the matching key. */
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AFTER_MATCHING_KEY
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}
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/**
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* Getter for the current record.
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*
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* @return The current record.
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*/
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T getRecord();
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/**
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* Skip to the next record of the database.
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*
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* @return true if has next, false otherwise
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* @throws ChangelogException
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* When database exception raised.
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*/
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boolean next() throws ChangelogException;
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/**
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* Release the resources and locks used by this Iterator. This method must be
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* called when the iterator is no longer used. Failure to do it could cause DB
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* deadlock.
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*/
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@Override
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void close();
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}
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