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1   /*
2    *
3    * Licensed to the Apache Software Foundation (ASF) under one
4    * or more contributor license agreements.  See the NOTICE file
5    * distributed with this work for additional information
6    * regarding copyright ownership.  The ASF licenses this file
7    * to you under the Apache License, Version 2.0 (the
8    * "License"); you may not use this file except in compliance
9    * with the License.  You may obtain a copy of the License at
10   *
11   * http://www.apache.org/licenses/LICENSE-2.0
12   *
13   * Unless required by applicable law or agreed to in writing, software
14   * distributed under the License is distributed on an "AS IS" BASIS,
15   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16   * See the License for the specific language governing permissions and
17   * limitations under the License.
18   */
19  
20  package org.apache.hadoop.hbase.coprocessor;
21  
22  import org.apache.hadoop.hbase.classification.InterfaceAudience;
23  import org.apache.hadoop.hbase.classification.InterfaceStability;
24  import org.apache.hadoop.hbase.Coprocessor;
25  import org.apache.hadoop.hbase.HBaseInterfaceAudience;
26  import org.apache.hadoop.hbase.HRegionInfo;
27  import org.apache.hadoop.hbase.regionserver.wal.HLogKey;
28  import org.apache.hadoop.hbase.regionserver.wal.WALEdit;
29  
30  import java.io.IOException;
31  
32  /**
33   * It's provided to have a way for coprocessors to observe, rewrite,
34   * or skip WALEdits as they are being written to the WAL.
35   *
36   * {@link org.apache.hadoop.hbase.coprocessor.RegionObserver} provides
37   * hooks for adding logic for WALEdits in the region context during reconstruction,
38   *
39   * Defines coprocessor hooks for interacting with operations on the
40   * {@link org.apache.hadoop.hbase.regionserver.wal.HLog}.
41   */
42  @InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.COPROC)
43  @InterfaceStability.Evolving
44  public interface WALObserver extends Coprocessor {
45  
46    /**
47     * Called before a {@link org.apache.hadoop.hbase.regionserver.wal.WALEdit}
48     * is writen to WAL.
49     *
50     * @param ctx
51     * @param info
52     * @param logKey
53     * @param logEdit
54     * @return true if default behavior should be bypassed, false otherwise
55     * @throws IOException
56     */
57    // TODO: return value is not used
58    boolean preWALWrite(ObserverContext<WALCoprocessorEnvironment> ctx,
59        HRegionInfo info, HLogKey logKey, WALEdit logEdit) throws IOException;
60  
61    /**
62     * Called after a {@link org.apache.hadoop.hbase.regionserver.wal.WALEdit}
63     * is writen to WAL.
64     *
65     * @param ctx
66     * @param info
67     * @param logKey
68     * @param logEdit
69     * @throws IOException
70     */
71    void postWALWrite(ObserverContext<WALCoprocessorEnvironment> ctx,
72        HRegionInfo info, HLogKey logKey, WALEdit logEdit) throws IOException;
73  }