View Javadoc

1   /**
2    * Licensed to the Apache Software Foundation (ASF) under one
3    * or more contributor license agreements.  See the NOTICE file
4    * distributed with this work for additional information
5    * regarding copyright ownership.  The ASF licenses this file
6    * to you under the Apache License, Version 2.0 (the
7    * "License"); you may not use this file except in compliance
8    * with the License.  You may obtain a copy of the License at
9    *
10   *     http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  
19  package org.apache.hadoop.hbase.replication.regionserver;
20  
21  import org.apache.commons.logging.Log;
22  import org.apache.commons.logging.LogFactory;
23  import org.apache.hadoop.classification.InterfaceAudience;
24  import org.apache.hadoop.conf.Configuration;
25  import org.apache.hadoop.fs.FileSystem;
26  import org.apache.hadoop.fs.Path;
27  import org.apache.hadoop.hbase.regionserver.wal.HLog;
28  import org.apache.hadoop.hbase.regionserver.wal.HLogFactory;
29  
30  import java.io.IOException;
31  
32  /**
33   * Wrapper class around HLog to help manage the implementation details
34   * such as compression.
35   */
36  @InterfaceAudience.Private
37  public class ReplicationHLogReaderManager {
38  
39    private static final Log LOG = LogFactory.getLog(ReplicationHLogReaderManager.class);
40    private final FileSystem fs;
41    private final Configuration conf;
42    private long position = 0;
43    private HLog.Reader reader;
44    private Path lastPath;
45  
46    /**
47     * Creates the helper but doesn't open any file
48     * Use setInitialPosition after using the constructor if some content needs to be skipped
49     * @param fs
50     * @param conf
51     */
52    public ReplicationHLogReaderManager(FileSystem fs, Configuration conf) {
53      this.fs = fs;
54      this.conf = conf;
55    }
56  
57    /**
58     * Opens the file at the current position
59     * @param path
60     * @return an HLog reader.
61     * @throws IOException
62     */
63    public HLog.Reader openReader(Path path) throws IOException {
64      // Detect if this is a new file, if so get a new reader else
65      // reset the current reader so that we see the new data
66      if (this.reader == null || !this.lastPath.equals(path)) {
67        this.closeReader();
68        this.reader = HLogFactory.createReader(this.fs, path, this.conf);
69        this.lastPath = path;
70      } else {
71        try {
72          this.reader.reset();
73        } catch (NullPointerException npe) {
74          throw new IOException("NPE resetting reader, likely HDFS-4380", npe);
75        }
76      }
77      return this.reader;
78    }
79  
80    /**
81     * Get the next entry, returned and also added in the array
82     * @return a new entry or null
83     * @throws IOException
84     */
85    public HLog.Entry readNextAndSetPosition() throws IOException {
86      HLog.Entry entry = this.reader.next();
87      // Store the position so that in the future the reader can start
88      // reading from here. If the above call to next() throws an
89      // exception, the position won't be changed and retry will happen
90      // from the last known good position
91      this.position = this.reader.getPosition();
92      // We need to set the CC to null else it will be compressed when sent to the sink
93      if (entry != null) {
94        entry.setCompressionContext(null);
95      }
96      return entry;
97    }
98  
99    /**
100    * Advance the reader to the current position
101    * @throws IOException
102    */
103   public void seek() throws IOException {
104     if (this.position != 0) {
105       this.reader.seek(this.position);
106     }
107   }
108 
109   /**
110    * Get the position that we stopped reading at
111    * @return current position, cannot be negative
112    */
113   public long getPosition() {
114     return this.position;
115   }
116 
117   public void setPosition(long pos) {
118     this.position = pos;
119   }
120 
121   /**
122    * Close the current reader
123    * @throws IOException
124    */
125   public void closeReader() throws IOException {
126     if (this.reader != null) {
127       this.reader.close();
128       this.reader = null;
129     }
130   }
131 
132   /**
133    * Tell the helper to reset internal state
134    */
135   void finishCurrentFile() {
136     this.position = 0;
137     try {
138       this.closeReader();
139     } catch (IOException e) {
140       LOG.warn("Unable to close reader", e);
141     }
142   }
143 
144 }