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 }