hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/metrics2/util/TestSampleQuantiles.java

/**
 * 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.metrics2.util;

import static org.junit.Assert.*;

import java.io.IOException;
import java.util.Arrays;
import java.util.Collections;
import java.util.Map;
import java.util.Random;

import org.junit.Before;
import org.junit.Test;

public class TestSampleQuantiles {

  static final Quantile[] quantiles = { new Quantile(0.50, 0.050),
      new Quantile(0.75, 0.025), new Quantile(0.90, 0.010),
      new Quantile(0.95, 0.005), new Quantile(0.99, 0.001) };

  SampleQuantiles estimator;

  @Before
  public void init() {
    estimator = new SampleQuantiles(quantiles);
  }

  /**
   * Check that the counts of the number of items in the window and sample are
   * incremented correctly as items are added.
   */
  @Test
  public void testCount() throws IOException {
    // Counts start off zero
    assertEquals(estimator.getCount(), 0);
    assertEquals(estimator.getSampleCount(), 0);
    
    // Snapshot should be null if there are no entries.
    assertNull(estimator.snapshot());

    // Count increment correctly by 1
    estimator.insert(1337);
    assertEquals(estimator.getCount(), 1);
    estimator.snapshot();
    assertEquals(estimator.getSampleCount(), 1);
    
    assertEquals(
        "50.00 %ile +/- 5.00%: 1337\n" +
        "75.00 %ile +/- 2.50%: 1337\n" +
        "90.00 %ile +/- 1.00%: 1337\n" +
        "95.00 %ile +/- 0.50%: 1337\n" +
        "99.00 %ile +/- 0.10%: 1337", estimator.toString());
  }

  /**
   * Check that counts and quantile estimates are correctly reset after a call
   * to {@link SampleQuantiles#clear()}.
   */
  @Test
  public void testClear() throws IOException {
    for (int i = 0; i < 1000; i++) {
      estimator.insert(i);
    }
    estimator.clear();
    assertEquals(estimator.getCount(), 0);
    assertEquals(estimator.getSampleCount(), 0);
    assertNull(estimator.snapshot());
  }

  /**
   * Correctness test that checks that absolute error of the estimate is within
   * specified error bounds for some randomly permuted streams of items.
   */
  @Test
  public void testQuantileError() throws IOException {
    final int count = 100000;
    Random r = new Random(0xDEADDEAD);
    Long[] values = new Long[count];
    for (int i = 0; i < count; i++) {
      values[i] = (long) (i + 1);
    }
    // Do 10 shuffle/insert/check cycles
    for (int i = 0; i < 10; i++) {
      System.out.println("Starting run " + i);
      Collections.shuffle(Arrays.asList(values), r);
      estimator.clear();
      for (int j = 0; j < count; j++) {
        estimator.insert(values[j]);
      }
      Map<Quantile, Long> snapshot;
      snapshot = estimator.snapshot();
      for (Quantile q : quantiles) {
        long actual = (long) (q.quantile * count);
        long error = (long) (q.error * count);
        long estimate = snapshot.get(q);
        System.out
            .println(String.format("Expected %d with error %d, estimated %d",
                actual, error, estimate));
        assertTrue(estimate <= actual + error);
        assertTrue(estimate >= actual - error);
      }
    }
  }
}