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 * Instead of calculate a whole time average, this class focus on the last N. The last N is stored 024 * in a circle array. 025 */ 026@InterfaceAudience.Private 027public class WindowMovingAverage extends MovingAverage { 028 protected final static int DEFAULT_SIZE = 5; 029 030 // The last n statistics. 031 protected long[] lastN; 032 // The index of the most recent statistics. 033 protected int mostRecent; 034 // If it travels a round. 035 protected boolean oneRound; 036 037 public WindowMovingAverage(String label) { 038 this(label, DEFAULT_SIZE); 039 } 040 041 public WindowMovingAverage(String label, int size) { 042 super(label); 043 this.lastN = new long[size <= 0 ? DEFAULT_SIZE : size]; 044 this.mostRecent = -1; 045 this.oneRound = false; 046 } 047 048 @Override 049 protected void updateMostRecentTime(long elapsed) { 050 int index = moveForwardMostRecentPosistion(); 051 lastN[index] = elapsed; 052 } 053 054 @Override 055 public double getAverageTime() { 056 return enoughStatistics() 057 ? (double) sum(getNumberOfStatistics()) / getNumberOfStatistics() 058 : (double) sum(getMostRecentPosistion() + 1) / (getMostRecentPosistion() + 1); 059 } 060 061 /** 062 * Check if there are enough statistics. 063 * @return true if lastN is full 064 */ 065 protected boolean enoughStatistics() { 066 return oneRound; 067 } 068 069 /** 070 * @return number of statistics 071 */ 072 protected int getNumberOfStatistics() { 073 return lastN.length; 074 } 075 076 /** 077 * Get statistics at index. 078 * @param index index of bar n 079 */ 080 protected long getStatisticsAtIndex(int index) { 081 if (index < 0 || index >= getNumberOfStatistics()) { 082 // This case should not happen, but a prudent check. 083 throw new IndexOutOfBoundsException(); 084 } 085 return lastN[index]; 086 } 087 088 /** 089 * @return index of most recent 090 */ 091 protected int getMostRecentPosistion() { 092 return mostRecent; 093 } 094 095 /** 096 * Move forward the most recent index. 097 * @return the most recent index 098 */ 099 protected int moveForwardMostRecentPosistion() { 100 int index = ++mostRecent; 101 if (!oneRound && index == getNumberOfStatistics()) { 102 // Back to the head of the lastN, from now on will 103 // start to evict oldest value. 104 oneRound = true; 105 } 106 mostRecent = index % getNumberOfStatistics(); 107 return mostRecent; 108 } 109 110 private long sum(int bound) { 111 long sum = 0; 112 for (int i = 0; i < bound; i++) { 113 sum += getStatisticsAtIndex(i); 114 } 115 return sum; 116 } 117}