001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019package org.apache.hadoop.hbase.util;
020
021import org.apache.yetus.audience.InterfaceAudience;
022
023/**
024 * Different from SMA {@link SimpleMovingAverage}, WeightedMovingAverage gives each data different
025 * weight. And it is based on {@link WindowMovingAverage}, such that it only focus on the last N.
026 */
027@InterfaceAudience.Private
028public class WeightedMovingAverage extends WindowMovingAverage {
029  private int[] coefficient;
030  private int denominator;
031
032  public WeightedMovingAverage(String label) {
033    this(label, DEFAULT_SIZE);
034  }
035
036  public WeightedMovingAverage(String label, int size) {
037    super(label, size);
038    int length = getNumberOfStatistics();
039    denominator = length * (length + 1) / 2;
040    coefficient = new int[length];
041    // E.g. default size is 5, coefficient should be [1, 2, 3, 4, 5]
042    for (int i = 0; i < length; i++) {
043      coefficient[i] = i + 1;
044    }
045  }
046
047  @Override
048  public double getAverageTime() {
049    if (!enoughStatistics()) {
050      return super.getAverageTime();
051    }
052    // only we get enough statistics, then start WMA.
053    double average = 0.0;
054    int coIndex = 0;
055    int length = getNumberOfStatistics();
056    // tmIndex, it points to the oldest data.
057    for (int tmIndex = (getMostRecentPosistion() + 1) % length;
058         coIndex < length;
059         coIndex++, tmIndex = (++tmIndex) % length) {
060      // start the multiplication from oldest to newest
061      average += coefficient[coIndex] * getStatisticsAtIndex(tmIndex);
062    }
063    return average / denominator;
064  }
065}