hbase-common/src/main/java/org/apache/hadoop/hbase/util/WeightedMovingAverage.java

   1 /*
   2  * Licensed to the Apache Software Foundation (ASF) under one
   3  * or more contributor license agreements.  See the NOTICE file
   4  * distributed with this work for additional information
   5  * regarding copyright ownership.  The ASF licenses this file
   6  * to you under the Apache License, Version 2.0 (the
   7  * "License"); you may not use this file except in compliance
   8  * with the License.  You may obtain a copy of the License at
   9  *
  10  *     http://www.apache.org/licenses/LICENSE-2.0
  11  *
  12  * Unless required by applicable law or agreed to in writing, software
  13  * distributed under the License is distributed on an "AS IS" BASIS,
  14  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  15  * See the License for the specific language governing permissions and
  16  * limitations under the License.
  17  */
  18
  19 package org.apache.hadoop.hbase.util;
  20
  21 import org.apache.yetus.audience.InterfaceAudience;
  22
  23 /**
  24  * Different from SMA {@link SimpleMovingAverage}, WeightedMovingAverage gives each data different
  25  * weight. And it is based on {@link WindowMovingAverage}, such that it only focus on the last N.
  26  */
  27 @InterfaceAudience.Private
  28 public class WeightedMovingAverage extends WindowMovingAverage {
  29   private int[] coefficient;
  30   private int denominator;
  31
  32   public WeightedMovingAverage(String label) {
  33     this(label, DEFAULT_SIZE);
  34   }
  35
  36   public WeightedMovingAverage(String label, int size) {
  37     super(label, size);
  38     int length = getNumberOfStatistics();
  39     denominator = length * (length + 1) / 2;
  40     coefficient = new int[length];
  41     // E.g. default size is 5, coefficient should be [1, 2, 3, 4, 5]
  42     for (int i = 0; i < length; i++) {
  43       coefficient[i] = i + 1;
  44     }
  45   }
  46
  47   @Override
  48   public double getAverageTime() {
  49     if (!enoughStatistics()) {
  50       return super.getAverageTime();
  51     }
  52     // only we get enough statistics, then start WMA.
  53     double average = 0.0;
  54     int coIndex = 0;
  55     int length = getNumberOfStatistics();
  56     // tmIndex, it points to the oldest data.
  57     for (int tmIndex = (getMostRecentPosistion() + 1) % length;
  58          coIndex < length;
  59          coIndex++, tmIndex = (++tmIndex) % length) {
  60       // start the multiplication from oldest to newest
  61       average += coefficient[coIndex] * getStatisticsAtIndex(tmIndex);
  62     }
  63     return average / denominator;
  64   }
  65 }