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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  package org.apache.hadoop.hbase.mapreduce;
20  
21  import java.io.IOException;
22  
23  import org.apache.commons.logging.Log;
24  import org.apache.commons.logging.LogFactory;
25  import org.apache.hadoop.hbase.classification.InterfaceAudience;
26  import org.apache.hadoop.hbase.classification.InterfaceStability;
27  import org.apache.hadoop.conf.Configurable;
28  import org.apache.hadoop.conf.Configuration;
29  import org.apache.hadoop.hbase.HBaseConfiguration;
30  import org.apache.hadoop.hbase.TableName;
31  import org.apache.hadoop.hbase.client.Connection;
32  import org.apache.hadoop.hbase.client.ConnectionFactory;
33  import org.apache.hadoop.hbase.client.RegionLocator;
34  import org.apache.hadoop.hbase.io.ImmutableBytesWritable;
35  import org.apache.hadoop.hbase.mapred.TableOutputFormat;
36  import org.apache.hadoop.hbase.util.Bytes;
37  import org.apache.hadoop.mapreduce.Partitioner;
38  
39  /**
40   * This is used to partition the output keys into groups of keys.
41   * Keys are grouped according to the regions that currently exist
42   * so that each reducer fills a single region so load is distributed.
43   *
44   * <p>This class is not suitable as partitioner creating hfiles
45   * for incremental bulk loads as region spread will likely change between time of
46   * hfile creation and load time. See {@link LoadIncrementalHFiles}
47   * and <a href="http://hbase.apache.org/book.html#arch.bulk.load">Bulk Load</a>.
48   *
49   * @param <KEY>  The type of the key.
50   * @param <VALUE>  The type of the value.
51   */
52  @InterfaceAudience.Public
53  @InterfaceStability.Stable
54  public class HRegionPartitioner<KEY, VALUE>
55  extends Partitioner<ImmutableBytesWritable, VALUE>
56  implements Configurable {
57  
58    private static final Log LOG = LogFactory.getLog(HRegionPartitioner.class);
59    private Configuration conf = null;
60    // Connection and locator are not cleaned up; they just die when partitioner is done.
61    private Connection connection;
62    private RegionLocator locator;
63    private byte[][] startKeys;
64  
65    /**
66     * Gets the partition number for a given key (hence record) given the total
67     * number of partitions i.e. number of reduce-tasks for the job.
68     *
69     * <p>Typically a hash function on a all or a subset of the key.</p>
70     *
71     * @param key  The key to be partitioned.
72     * @param value  The entry value.
73     * @param numPartitions  The total number of partitions.
74     * @return The partition number for the <code>key</code>.
75     * @see org.apache.hadoop.mapreduce.Partitioner#getPartition(
76     *   java.lang.Object, java.lang.Object, int)
77     */
78    @Override
79    public int getPartition(ImmutableBytesWritable key,
80        VALUE value, int numPartitions) {
81      byte[] region = null;
82      // Only one region return 0
83      if (this.startKeys.length == 1){
84        return 0;
85      }
86      try {
87        // Not sure if this is cached after a split so we could have problems
88        // here if a region splits while mapping
89        region = this.locator.getRegionLocation(key.get()).getRegionInfo().getStartKey();
90      } catch (IOException e) {
91        LOG.error(e);
92      }
93      for (int i = 0; i < this.startKeys.length; i++){
94        if (Bytes.compareTo(region, this.startKeys[i]) == 0 ){
95          if (i >= numPartitions-1){
96            // cover if we have less reduces then regions.
97            return (Integer.toString(i).hashCode()
98                & Integer.MAX_VALUE) % numPartitions;
99          }
100         return i;
101       }
102     }
103     // if above fails to find start key that match we need to return something
104     return 0;
105   }
106 
107   /**
108    * Returns the current configuration.
109    *
110    * @return The current configuration.
111    * @see org.apache.hadoop.conf.Configurable#getConf()
112    */
113   @Override
114   public Configuration getConf() {
115     return conf;
116   }
117 
118   /**
119    * Sets the configuration. This is used to determine the start keys for the
120    * given table.
121    *
122    * @param configuration  The configuration to set.
123    * @see org.apache.hadoop.conf.Configurable#setConf(
124    *   org.apache.hadoop.conf.Configuration)
125    */
126   @Override
127   public void setConf(Configuration configuration) {
128     this.conf = HBaseConfiguration.create(configuration);
129     try {
130       this.connection = ConnectionFactory.createConnection(HBaseConfiguration.create(conf));
131       TableName tableName = TableName.valueOf(conf.get(TableOutputFormat.OUTPUT_TABLE));
132       this.locator = this.connection.getRegionLocator(tableName);
133     } catch (IOException e) {
134       LOG.error(e);
135     }
136     try {
137       this.startKeys = this.locator.getStartKeys();
138     } catch (IOException e) {
139       LOG.error(e);
140     }
141   }
142 }