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HashRangePartitionerFactory xref
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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.giraph.partition;
20  
21  import org.apache.hadoop.io.Writable;
22  import org.apache.hadoop.io.WritableComparable;
23  
24  import com.google.common.primitives.UnsignedInts;
25  
26  /**
27   * Divides the vertices into partitions by their hash code using ranges of the
28   * hash space.
29   *
30   * @param <I> Vertex index value
31   * @param <V> Vertex value
32   * @param <E> Edge value
33   */
34  @SuppressWarnings("rawtypes")
35  public class HashRangePartitionerFactory<I extends WritableComparable,
36      V extends Writable, E extends Writable>
37      extends GraphPartitionerFactory<I, V, E> {
38  
39    /** A transformed hashCode() must be strictly smaller than this. */
40    private static final long HASH_LIMIT = 2L * Integer.MAX_VALUE + 2L;
41  
42    @Override
43    public int getPartition(I id, int partitionCount, int workerCount) {
44      long unsignedHashCode = UnsignedInts.toLong(id.hashCode());
45      // The reader can verify that unsignedHashCode of HASH_LIMIT - 1 yields
46      // index of size - 1, and unsignedHashCode of 0 yields index of 0.
47      return (int) ((unsignedHashCode * partitionCount) / HASH_LIMIT);
48    }
49  
50    @Override
51    public int getWorker(int partition, int partitionCount, int workerCount) {
52      return partition % workerCount;
53    }
54  }