Mercurial > hg > blitz_stable

annotate src/org/dancres/blitz/txn/batch/ConcurrentWriteBatcher.java @ 0:3dc0c5604566

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Initial checkin of blitz 2.0 fcs - no installer yet.
author Dan Creswell <dan.creswell@gmail.com>
date Sat, 21 Mar 2009 11:00:06 +0000
parents
children 4580bb12db30
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rev   line source
0
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
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1 package org.dancres.blitz.txn.batch;
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2
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3 import java.io.IOException;
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4 import java.io.Serializable;
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5
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6 import java.util.ArrayList;
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7
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8 import java.util.logging.Level;
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9
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10 import org.prevayler.Prevayler;
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11 import org.prevayler.PrevalentSystem;
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12 import org.prevayler.Command;
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13
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14 import org.prevayler.implementation.SnapshotPrevayler;
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15 import org.prevayler.implementation.Snapshotter;
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16
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17 /**
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18 <p>Batches commands issued in the same time period together in an attempt
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19 to improve log throughput via Prevayler.</p>
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20
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21 <p>Batch-writing can reduce the number of forced flushes to disk whilst
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22 increasing the amount of data written with each flush. This has a
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23 positive effect on throughput under concurrent load.</p>
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24
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25 <p>Time is specified in ms, first thread into barrier waits this amount
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26 of time for other writers. Other writers entering the barrier are
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27 now blocked until the first entrant commits all writes to log. When first
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28 thread awakes, all writes are done as a group followed by a single sync.</p>
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29
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30 <p>Unlike <code>WriteBatcher</code>, this version supports more concurrency
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31 allowing for queuing of the next batch of log entries whilst the current
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32 bunch is being written.</p>
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33 */
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34 public class ConcurrentWriteBatcher implements SnapshotPrevayler {
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35 private SnapshotPrevayler thePrevayler;
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36
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37 private boolean amFirst = true;
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38
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39 private ArrayList theWrites = new ArrayList();
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40
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41 // Might be able to buff up to 60ms which gives average of 30 but
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42 // we'll see.
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43 private long theWindowTime = 20;
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44
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45 public ConcurrentWriteBatcher(SnapshotPrevayler aPrevayler,
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46 long aWindowTime) {
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47
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48 thePrevayler = aPrevayler;
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49 theWindowTime = aWindowTime;
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50 }
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51
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52 /**
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53 * Returns the underlying PrevalentSystem.
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54 */
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55 public PrevalentSystem system() {
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56 return thePrevayler.system();
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57 }
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58
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59 public Serializable executeCommand(Command aCommand) throws Exception {
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60 return write(aCommand);
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61 }
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62
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63 public Serializable executeCommand(Command aCommand, boolean sync)
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64 throws Exception {
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65 return write(aCommand);
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66 }
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67
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68 private Serializable write(Command aComm) throws Exception {
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69 WriteRequest myReq = new WriteRequest(aComm);
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70
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71 boolean wasFirst = false;
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72
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73 WriteRequest[] myRequests = null;
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74
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75 synchronized(this) {
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76 if (amFirst) {
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77 theWrites.add(myReq);
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78 amFirst = false;
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79 wasFirst = true;
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80
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81 try {
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82 wait(theWindowTime);
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83 } catch (InterruptedException anIE) {
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84 }
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85
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86 myRequests = new WriteRequest[theWrites.size()];
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87 myRequests = (WriteRequest[]) theWrites.toArray(myRequests);
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88
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89 theWrites.clear();
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90 amFirst = true;
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91
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92 } else {
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93 theWrites.add(myReq);
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94 }
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95 }
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96
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97 if (wasFirst) {
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98 flushAll(myRequests);
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99 }
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100
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101 return myReq.getResult();
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102 }
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103
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104 public Snapshotter takeSnapshot() throws IOException {
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105 return thePrevayler.takeSnapshot();
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106 }
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107
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108 private void flushAll(WriteRequest[] aRequests) {
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109 int myLast = aRequests.length - 1;
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110
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111 if (WriteBatcher.theLogger.isLoggable(Level.FINE))
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112 WriteBatcher.theLogger.log(Level.FINE,
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113 "Flushing " +
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114 aRequests.length + " to log");
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115
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116 // Do all writes, last with sync
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117 for (int i = 0; i < aRequests.length; i++) {
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118 WriteRequest myReq = aRequests[i];
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119
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120 myReq.execute(thePrevayler, (i == myLast));
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121 }
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122 }
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123
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124 private static class WriteRequest {
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125 private Command theCommand;
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126
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127 private Exception theException;
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128 private Serializable theResult;
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129
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130 private boolean isDone;
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131
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132 WriteRequest(Command aCommand) {
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133 theCommand = aCommand;
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134 }
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135
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136 void execute(Prevayler aPrev, boolean doSync) {
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137 try {
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138 theResult = aPrev.executeCommand(theCommand, doSync);
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139 } catch (Exception anE) {
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140 theException = anE;
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141 } finally {
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142 synchronized(this) {
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143 isDone = true;
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144 notify();
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145 }
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146 }
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147 }
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148
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149 Serializable getResult() throws Exception{
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150 synchronized(this) {
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151 while (!isDone) {
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152 try {
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153 wait();
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154 } catch (InterruptedException anIE) {
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155 }
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156 }
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157
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158 if (theException != null)
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159 throw theException;
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160 else
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161 return theResult;
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162 }
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163 }
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164 }
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165 }