hbase-common/src/main/java/org/apache/hadoop/hbase/util/WindowMovingAverage.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  * Instead of calculate a whole time average, this class focus on the last N.
  25  * The last N is stored in a circle array.
  26  */
  27 @InterfaceAudience.Private
  28 public class WindowMovingAverage extends MovingAverage {
  29   protected final static int DEFAULT_SIZE = 5;
  30
  31   // The last n statistics.
  32   protected long[] lastN;
  33   // The index of the most recent statistics.
  34   protected int mostRecent;
  35   // If it travels a round.
  36   protected boolean oneRound;
  37
  38   public WindowMovingAverage(String label) {
  39     this(label, DEFAULT_SIZE);
  40   }
  41
  42   public WindowMovingAverage(String label, int size) {
  43     super(label);
  44     this.lastN = new long[size <= 0 ? DEFAULT_SIZE : size];
  45     this.mostRecent = -1;
  46     this.oneRound = false;
  47   }
  48
  49   @Override
  50   protected void updateMostRecentTime(long elapsed) {
  51     int index = moveForwardMostRecentPosistion();
  52     lastN[index] = elapsed;
  53   }
  54
  55   @Override
  56   public double getAverageTime() {
  57     return enoughStatistics() ?
  58       (double) sum(getNumberOfStatistics()) / getNumberOfStatistics() :
  59       (double) sum(getMostRecentPosistion() + 1) / (getMostRecentPosistion() + 1);
  60   }
  61
  62   /**
  63    * Check if there are enough statistics.
  64    * @return true if lastN is full
  65    */
  66   protected boolean enoughStatistics() {
  67     return oneRound;
  68   }
  69
  70   /**
  71    * @return number of statistics
  72    */
  73   protected int getNumberOfStatistics() {
  74     return lastN.length;
  75   }
  76
  77   /**
  78    * Get statistics at index.
  79    * @param index index of bar
  80    * @return statistics
  81    */
  82   protected long getStatisticsAtIndex(int index) {
  83     if (index < 0 || index >= getNumberOfStatistics()) {
  84       // This case should not happen, but a prudent check.
  85       throw new IndexOutOfBoundsException();
  86     }
  87     return lastN[index];
  88   }
  89
  90   /**
  91    * @return index of most recent
  92    */
  93   protected int getMostRecentPosistion() {
  94     return mostRecent;
  95   }
  96
  97   /**
  98    * Move forward the most recent index.
  99    * @return the most recent index
 100    */
 101   protected int moveForwardMostRecentPosistion() {
 102     int index = ++mostRecent;
 103     if (!oneRound && index == getNumberOfStatistics()) {
 104       // Back to the head of the lastN, from now on will
 105       // start to evict oldest value.
 106       oneRound = true;
 107     }
 108     mostRecent = index % getNumberOfStatistics();
 109     return mostRecent;
 110   }
 111
 112   private long sum(int bound) {
 113     long sum = 0;
 114     for (int i = 0; i < bound; i++) {
 115       sum += getStatisticsAtIndex(i);
 116     }
 117     return sum;
 118   }
 119 }