hbase-metrics/src/test/java/org/apache/hadoop/hbase/metrics/impl/TestHistogramImpl.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.hbase.metrics.impl;

import static org.junit.Assert.assertEquals;

import java.util.stream.IntStream;
import org.apache.hadoop.hbase.HBaseClassTestRule;
import org.apache.hadoop.hbase.metrics.Snapshot;
import org.apache.hadoop.hbase.testclassification.SmallTests;
import org.junit.ClassRule;
import org.junit.Test;
import org.junit.experimental.categories.Category;

/**
 * Test case for {@link HistogramImpl}
 */
@Category(SmallTests.class)
public class TestHistogramImpl {

  @ClassRule
  public static final HBaseClassTestRule CLASS_RULE =
      HBaseClassTestRule.forClass(TestHistogramImpl.class);

  @Test
  public void testUpdate() {
    HistogramImpl histogram = new HistogramImpl();

    assertEquals(0, histogram.getCount());

    histogram.update(0);
    assertEquals(1, histogram.getCount());

    histogram.update(10);
    assertEquals(2, histogram.getCount());

    histogram.update(20);
    histogram.update(30);

    assertEquals(4, histogram.getCount());
  }

  @Test
  public void testSnapshot() {
    HistogramImpl histogram = new HistogramImpl();
    IntStream.range(0, 100).forEach(histogram::update);

    Snapshot snapshot = histogram.snapshot();

    assertEquals(100, snapshot.getCount());
    assertEquals(49, snapshot.getMedian());
    assertEquals(49, snapshot.getMean());
    assertEquals(0, snapshot.getMin());
    assertEquals(99, snapshot.getMax());
    assertEquals(24, snapshot.get25thPercentile());
    assertEquals(74, snapshot.get75thPercentile());
    assertEquals(89, snapshot.get90thPercentile());
    assertEquals(94, snapshot.get95thPercentile());
    assertEquals(97, snapshot.get98thPercentile());
    assertEquals(98, snapshot.get99thPercentile());
    assertEquals(98, snapshot.get999thPercentile());

    assertEquals(100, snapshot.getCountAtOrBelow(50));

    // check that histogram is reset.
    assertEquals(100, histogram.getCount()); // count does not reset

    // put more data after reset
    IntStream.range(100, 200).forEach(histogram::update);

    assertEquals(200, histogram.getCount());

    snapshot = histogram.snapshot();
    assertEquals(100, snapshot.getCount()); // only 100 more events
    assertEquals(150, snapshot.getMedian());
    assertEquals(149, snapshot.getMean());
    assertEquals(100, snapshot.getMin());
    assertEquals(199, snapshot.getMax());
    assertEquals(125, snapshot.get25thPercentile());
    assertEquals(175, snapshot.get75thPercentile());
    assertEquals(190, snapshot.get90thPercentile());
    assertEquals(195, snapshot.get95thPercentile());
    assertEquals(198, snapshot.get98thPercentile());
    assertEquals(199, snapshot.get99thPercentile());
    assertEquals(199, snapshot.get999thPercentile());

    IntStream.range(500, 1000).forEach(histogram::update);

    snapshot = histogram.snapshot();

    assertEquals(500, snapshot.getCount());
    assertEquals(749, snapshot.getMedian());
    assertEquals(749, snapshot.getMean());
    assertEquals(500, snapshot.getMin());
    assertEquals(999, snapshot.getMax());
    assertEquals(624, snapshot.get25thPercentile());
    assertEquals(874, snapshot.get75thPercentile());
    assertEquals(949, snapshot.get90thPercentile());
    assertEquals(974, snapshot.get95thPercentile());
    assertEquals(989, snapshot.get98thPercentile());
    assertEquals(994, snapshot.get99thPercentile());
    assertEquals(998, snapshot.get999thPercentile());

  }
}