org.apache.hadoop.mapreduce.lib.partition.TestRehashPartitioner.java Source code

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Here is the source code for org.apache.hadoop.mapreduce.lib.partition.TestRehashPartitioner.java

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/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.hadoop.mapreduce.lib.partition;

import static org.junit.Assert.*;

import java.util.Arrays;
import java.util.Collections;

import org.apache.commons.lang.ArrayUtils;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.NullWritable;

import org.junit.*;

public class TestRehashPartitioner {

    /** number of partitions */
    private static final int PARTITIONS = 32;

    /** step in sequence */
    private static final int STEP = 3;

    /** end of test sequence */
    private static final int END = 100000;

    /** maximum error for considering too big/small bucket */
    private static final double MAX_ERROR = 0.20;

    /** maximum number of oddly sized buckets */
    private static final double MAX_BADBUCKETS = 0.10;

    /** test partitioner for patterns */
    @Test
    public void testPatterns() {
        int results[] = new int[PARTITIONS];
        RehashPartitioner<IntWritable, NullWritable> p = new RehashPartitioner<IntWritable, NullWritable>();
        /* test sequence 4, 8, 12, ... 128 */
        for (int i = 0; i < END; i += STEP) {
            results[p.getPartition(new IntWritable(i), null, PARTITIONS)]++;
        }
        int badbuckets = 0;
        Integer min = Collections.min(Arrays.asList(ArrayUtils.toObject(results)));
        Integer max = Collections.max(Arrays.asList(ArrayUtils.toObject(results)));
        Integer avg = (int) Math.round((max + min) / 2.0);
        System.out.println("Dumping buckets distribution: min=" + min + " avg=" + avg + " max=" + max);
        for (int i = 0; i < PARTITIONS; i++) {
            double var = (results[i] - avg) / (double) (avg);
            System.out.println("bucket " + i + " " + results[i] + " items, variance " + var);
            if (Math.abs(var) > MAX_ERROR)
                badbuckets++;
        }
        System.out.println(badbuckets + " of " + PARTITIONS + " are too small or large buckets");
        assertTrue("too many overflow buckets", badbuckets < PARTITIONS * MAX_BADBUCKETS);
    }
}