Mercurial > hg > blitz_stable

annotate src/org/dancres/blitz/entry/WriteScheduler.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
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children
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0
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
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1 package org.dancres.blitz.entry;
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2
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3 import java.io.IOException;
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4
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5 import java.util.HashMap;
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6
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7 import java.util.logging.Level;
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8
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9 import org.dancres.blitz.oid.OID;
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10 import org.dancres.blitz.entry.ci.CacheIndexer;
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11
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12 /**
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13 <p> Transactional writes add a further complication to the caching process
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14 because, whilst they can be flushed from SleeveCache, they can't necessarily
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15 be written to disk. Consider the case where a transaction starts and
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16 writes an entry, other activity causes that entry to be flushed from
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17 SleeveCache into the asynchronous write queue and then saved to disk.
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18 The system now crashes prior to the original writing transaction issuing
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19 a successful prepare. At recovery, we will have an additional entry on
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20 disk unprotected by transactional locks and it would be valid for matching.
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21 </p>
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22
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23 <p> WriteScheduler helps solve this problem by supporting "Transient"
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24 EntrySleeveImpls. EntrySleeveImpls marked as transient are held in
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25 WriteScheduler but not schedule to be written to disk. WriteScheduler
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26 maintains an index of all Entry's to assist in searching so these
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27 Transient's are available for matching. When a transaction commits, the
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28 Transient mark is removed from EntrySleeveImpls (these sleeves must be
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29 reloaded into SleeveCache for this to happen) and they are re-submitted to
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30 WriteScheduler at which point they are scheduled for writing. </p>
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31
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32 <p> Thus, until a transaction is commited/aborted, any EntrySleeveImpls
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33 written are marked Transient. During commit/abort, these Sleeves have the
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34 mark removed and are thus eligible for writing to disk. </p>
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35 */
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36 class WriteScheduler {
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37 private HashMap theTransients = new HashMap();
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38
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39 private WriteBuffer theBuffer;
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40 private String theType;
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41
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42 WriteScheduler(EntryEditor anEditor) {
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43 theType = anEditor.getType();
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44 theBuffer = new WriteBuffer(anEditor);
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45 }
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46
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47 public int getSize() {
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48 throw new org.dancres.util.NotImplementedException();
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49 }
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50
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51 void add(EntrySleeveImpl aSleeve) throws IOException {
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52 /*
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53 Cache has no concept of dirty, it flushes content out of a block
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54 whenever it wishes to use the block for something else. So,
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55 it's possible we'll be asked to flush an empty block.
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56 */
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57 if (aSleeve == null)
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58 return;
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59
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60 /*
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61 Whether the sleeve is dirty or not, if it's pinned we remember it.
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62 Pinned implies some entity will do more with this sleeve later
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63 including potentially dirtying state which might be clean at
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64 this stage. Thus we must remember the state clean or dirty until
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65 the pin is released.
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66 */
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67 SleeveState myState = aSleeve.getState();
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68
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69 if (myState.test(SleeveState.PINNED)) {
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70 synchronized(theTransients) {
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71 theTransients.put(aSleeve.getOID(), aSleeve);
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72 }
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73
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74 return;
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75 }
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76
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77 /*
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78 Cache flushed the entry - do we need to save it?
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79 */
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80 if (!aSleeve.isDirty())
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81 return;
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82
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83 boolean dontWrite = myState.test(SleeveState.NOT_ON_DISK) &&
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84 myState.test(SleeveState.DELETED);
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85
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86 /*
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87 If we're not writing this entry, clear it from the indexer now
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88 otherwise leave it to the write buffer to do when it's pushed
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89 the entry to disk
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90 if (dontWrite) {
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91 CacheIndexer.getIndexer(theType).flushed(aSleeve);
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92 }
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93 */
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94
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95 synchronized(theTransients) {
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96 theTransients.remove(aSleeve.getOID());
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97
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98 if (!dontWrite)
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99 theBuffer.add(aSleeve);
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100 }
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101
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102 /*
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103 Note we do not manage NOT_ON_DISK - this is dealt with in the
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104 WriteBuffer as it's vital state it needs to determine whether or
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105 not to actually update disk.
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106 */
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107 aSleeve.clearDirty();
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108 }
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109
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110 EntrySleeveImpl dirtyRead(OID aUID) {
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111 EntrySleeveImpl mySleeve = null;
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112
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113 synchronized(theTransients) {
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114 mySleeve = (EntrySleeveImpl) theTransients.get(aUID);
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115 }
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116
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117 if (mySleeve == null)
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118 mySleeve = theBuffer.dirtyRead(aUID);
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119
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120 return mySleeve;
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121 }
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122 }