001/*
002 * CDDL HEADER START
003 *
004 * The contents of this file are subject to the terms of the
005 * Common Development and Distribution License, Version 1.0 only
006 * (the "License").  You may not use this file except in compliance
007 * with the License.
008 *
009 * You can obtain a copy of the license at legal-notices/CDDLv1_0.txt
010 * or http://forgerock.org/license/CDDLv1.0.html.
011 * See the License for the specific language governing permissions
012 * and limitations under the License.
013 *
014 * When distributing Covered Code, include this CDDL HEADER in each
015 * file and include the License file at legal-notices/CDDLv1_0.txt.
016 * If applicable, add the following below this CDDL HEADER, with the
017 * fields enclosed by brackets "[]" replaced with your own identifying
018 * information:
019 *      Portions Copyright [yyyy] [name of copyright owner]
020 *
021 * CDDL HEADER END
022 *
023 *
024 *      Copyright 2013-2015 ForgeRock AS
025 */
026package org.opends.server.replication.server.changelog.api;
027
028import java.io.Closeable;
029import java.util.Objects;
030
031import org.opends.server.replication.common.CSN;
032
033/**
034 * Generic cursor interface into the changelog database. Once it is not used
035 * anymore, a cursor must be closed to release all the resources into the
036 * database.
037 * <p>
038 * The cursor provides a java.sql.ResultSet like API : it is positioned before
039 * the first requested record and needs to be moved forward by calling
040 * {@link DBCursor#next()}.
041 * <p>
042 * Usage:
043 * <pre>
044 *  DBCursor cursor = ...;
045 *  try {
046 *    while (cursor.next()) {
047 *      Record record = cursor.getRecord();
048 *      // ... can call cursor.getRecord() again: it will return the same result
049 *    }
050 *  }
051 *  finally {
052 *    close(cursor);
053 *  }
054 * }
055 * </pre>
056 *
057 * A cursor can be initialised from a key, using a {@code KeyMatchingStrategy} and
058 * a {@code PositionStrategy}, to determine the exact starting position.
059 * <p>
060 * Let's call Kp the highest key lower than K and Kn the lowest key higher
061 * than K : Kp &lt; K &lt; Kn
062 * <ul>
063 *  <li>When using EQUAL_TO_KEY on key K :
064 *   <ul>
065 *    <li>with ON_MATCHING_KEY, cursor is positioned on key K (if K exists in log),
066 *        otherwise it is empty</li>
067 *    <li>with AFTER_MATCHING_KEY, cursor is positioned on key Kn (if K exists in log),
068 *        otherwise it is empty</li>
069 *   </ul>
070 *  </li>
071 *  <li>When using LESS_THAN_OR_EQUAL_TO_KEY on key K :
072 *   <ul>
073 *    <li>with ON_MATCHING_KEY, cursor is positioned on key K (if K exists in log)
074 *        or else Kp (if Kp exists in log), otherwise it is empty</li>
075 *    <li>with AFTER_MATCHING_KEY, cursor is positioned on key Kn (if Kp or K exist in log),
076 *        otherwise it is empty</li>
077 *   </ul>
078 *  </li>
079 *  <li>When using GREATER_THAN_OR_EQUAL_TO_KEY on key K :
080 *   <ul>
081 *    <li>with ON_MATCHING_KEY, cursor is positioned on key K (if K exists in log)
082 *        or else Kn (if Kn exists in log), otherwise it is empty</li>
083 *    <li>with AFTER_MATCHING_KEY, cursor is positioned on key Kn (if K or Kn exist in log),
084 *        otherwise it is empty</li>
085 *   </ul>
086 *  </li>
087 * </ul>
088 *
089 * @param <T>
090 *          type of the record being returned
091 * \@NotThreadSafe
092 */
093public interface DBCursor<T> extends Closeable
094{
095
096  /**
097   * Represents a cursor key matching strategy, which allow to choose if only
098   * the exact key must be found or if any key equal or lower/higher should match.
099   */
100  public enum KeyMatchingStrategy {
101    /** Matches if the key or a lower key is found. */
102    LESS_THAN_OR_EQUAL_TO_KEY,
103    /** Matches only if the exact key is found. */
104    EQUAL_TO_KEY,
105    /** Matches if the key or a greater key is found. */
106    GREATER_THAN_OR_EQUAL_TO_KEY
107  }
108
109  /**
110   * Represents a cursor positioning strategy, which allow to choose if the start point
111   * corresponds to the record at the provided key or the record just after the provided
112   * key.
113   */
114  public enum PositionStrategy {
115    /** Start point is on the matching key. */
116    ON_MATCHING_KEY,
117    /** Start point is after the matching key. */
118    AFTER_MATCHING_KEY
119  }
120
121  /** Options to create a cursor. */
122  public static final class CursorOptions
123  {
124    private final KeyMatchingStrategy keyMatchingStrategy;
125    private final PositionStrategy positionStrategy;
126    private final CSN defaultCSN;
127
128    /**
129     * Creates options with provided strategies.
130     *
131     * @param keyMatchingStrategy
132     *          The key matching strategy
133     * @param positionStrategy
134     *          The position strategy
135     */
136    public CursorOptions(KeyMatchingStrategy keyMatchingStrategy, PositionStrategy positionStrategy)
137    {
138      this(keyMatchingStrategy, positionStrategy, null);
139    }
140
141    /**
142     * Creates options with provided strategies and default CSN.
143     *
144     * @param keyMatchingStrategy
145     *          The key matching strategy
146     * @param positionStrategy
147     *          The position strategy
148     * @param defaultCSN
149     *          When creating a replica DB Cursor, this is the default CSN to
150     *          use for replicas which do not have an associated CSN
151     */
152    public CursorOptions(KeyMatchingStrategy keyMatchingStrategy, PositionStrategy positionStrategy, CSN defaultCSN)
153    {
154      this.keyMatchingStrategy = keyMatchingStrategy;
155      this.positionStrategy = positionStrategy;
156      this.defaultCSN = defaultCSN;
157    }
158
159    /**
160     * Returns the key matching strategy.
161     *
162     * @return the key matching strategy
163     */
164    public KeyMatchingStrategy getKeyMatchingStrategy()
165    {
166      return keyMatchingStrategy;
167    }
168
169    /**
170     * Returns the position strategy.
171     *
172     * @return the position strategy
173     */
174    public PositionStrategy getPositionStrategy()
175    {
176      return positionStrategy;
177    }
178
179    /**
180     * Returns the default CSN.
181     *
182     * @return the default CSN
183     */
184    public CSN getDefaultCSN()
185    {
186      return defaultCSN;
187    }
188
189    @Override
190    public boolean equals(Object obj)
191    {
192      if (this == obj) {
193        return true;
194      }
195      if (obj instanceof CursorOptions) {
196        CursorOptions other = (CursorOptions) obj;
197        return keyMatchingStrategy == other.keyMatchingStrategy
198            && positionStrategy == other.positionStrategy
199            && Objects.equals(defaultCSN, other.defaultCSN);
200      }
201      return false;
202    }
203
204    @Override
205    public int hashCode()
206    {
207      final int prime = 31;
208      int result = 1;
209      result = prime * result + ((keyMatchingStrategy == null) ? 0 : keyMatchingStrategy.hashCode());
210      result = prime * result + ((positionStrategy == null) ? 0 : positionStrategy.hashCode());
211      result = prime * result + ((defaultCSN == null) ? 0 : defaultCSN.hashCode());
212      return result;
213    }
214
215    @Override
216    public String toString()
217    {
218      return getClass().getSimpleName()
219          + " [keyMatchingStrategy=" + keyMatchingStrategy
220          + ", positionStrategy=" + positionStrategy
221          + ", defaultCSN=" + defaultCSN + "]";
222    }
223  }
224
225  /**
226   * Getter for the current record.
227   *
228   * @return The current record.
229   */
230  T getRecord();
231
232  /**
233   * Skip to the next record of the database.
234   *
235   * @return true if has next, false otherwise
236   * @throws ChangelogException
237   *           When database exception raised.
238   */
239  boolean next() throws ChangelogException;
240
241  /**
242   * Release the resources and locks used by this Iterator. This method must be
243   * called when the iterator is no longer used. Failure to do it could cause DB
244   * deadlock.
245   */
246  @Override
247  void close();
248}