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 */
018package org.apache.hadoop.hbase.util;
019
020import org.apache.yetus.audience.InterfaceAudience;
021
022/**
023 * Different from SMA {@link SimpleMovingAverage}, WeightedMovingAverage gives each data different
024 * weight. And it is based on {@link WindowMovingAverage}, such that it only focus on the last N.
025 */
026@InterfaceAudience.Private
027public class WeightedMovingAverage extends WindowMovingAverage {
028  private int[] coefficient;
029  private int denominator;
030
031  public WeightedMovingAverage(String label) {
032    this(label, DEFAULT_SIZE);
033  }
034
035  public WeightedMovingAverage(String label, int size) {
036    super(label, size);
037    int length = getNumberOfStatistics();
038    denominator = length * (length + 1) / 2;
039    coefficient = new int[length];
040    // E.g. default size is 5, coefficient should be [1, 2, 3, 4, 5]
041    for (int i = 0; i < length; i++) {
042      coefficient[i] = i + 1;
043    }
044  }
045
046  @Override
047  public double getAverageTime() {
048    if (!enoughStatistics()) {
049      return super.getAverageTime();
050    }
051    // only we get enough statistics, then start WMA.
052    double average = 0.0;
053    int coIndex = 0;
054    int length = getNumberOfStatistics();
055    // tmIndex, it points to the oldest data.
056    for (int tmIndex = (getMostRecentPosistion() + 1) % length; coIndex
057        < length; coIndex++, tmIndex = (++tmIndex) % length) {
058      // start the multiplication from oldest to newest
059      average += coefficient[coIndex] * getStatisticsAtIndex(tmIndex);
060    }
061    return average / denominator;
062  }
063}