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1   /*
2    * Copyright 2010 The Apache Software Foundation
3    *
4    * Licensed to the Apache Software Foundation (ASF) under one
5    * or more contributor license agreements.  See the NOTICE file
6    * distributed with this work for additional information
7    * regarding copyright ownership.  The ASF licenses this file
8    * to you under the Apache License, Version 2.0 (the
9    * "License"); you may not use this file except in compliance
10   * with the License.  You may obtain a copy of the License at
11   *
12   * http://www.apache.org/licenses/LICENSE-2.0
13   *
14   * Unless required by applicable law or agreed to in writing, software
15   * distributed under the License is distributed on an "AS IS" BASIS,
16   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
17   * See the License for the specific language governing permissions and
18   * limitations under the License.
19   */
20  
21  package org.apache.hadoop.hbase.coprocessor;
22  
23  import org.apache.hadoop.hbase.Coprocessor;
24  import org.apache.hadoop.hbase.HRegionInfo;
25  import org.apache.hadoop.hbase.regionserver.wal.HLogKey;
26  import org.apache.hadoop.hbase.regionserver.wal.WALEdit;
27  
28  import java.io.IOException;
29  
30  /**
31   * It's provided to have a way for coprocessors to observe, rewrite,
32   * or skip WALEdits as they are being written to the WAL.
33   *
34   * {@link org.apache.hadoop.hbase.coprocessor.RegionObserver} provides
35   * hooks for adding logic for WALEdits in the region context during reconstruction,
36   *
37   * Defines coprocessor hooks for interacting with operations on the
38   * {@link org.apache.hadoop.hbase.regionserver.wal.HLog}.
39   */
40  public interface WALObserver extends Coprocessor {
41  
42    /**
43     * Called before a {@link org.apache.hadoop.hbase.regionserver.wal.WALEdit}
44     * is writen to WAL.
45     *
46     * @param ctx
47     * @param info
48     * @param logKey
49     * @param logEdit
50     * @return true if default behavior should be bypassed, false otherwise
51     * @throws IOException
52     */
53    boolean preWALWrite(ObserverContext<WALCoprocessorEnvironment> ctx,
54        HRegionInfo info, HLogKey logKey, WALEdit logEdit) throws IOException;
55  
56    /**
57     * Called after a {@link org.apache.hadoop.hbase.regionserver.wal.WALEdit}
58     * is writen to WAL.
59     *
60     * @param ctx
61     * @param info
62     * @param logKey
63     * @param logEdit
64     * @throws IOException
65     */
66    void postWALWrite(ObserverContext<WALCoprocessorEnvironment> ctx,
67        HRegionInfo info, HLogKey logKey, WALEdit logEdit) throws IOException;
68  }