[计算机软件及应用]buffercache

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1、BufferCacheWaitsInThisSectionlatch:cachebufferschainslatch:cachebufferslruchainlatch:cachebufferhandlesFreeBufferWaitBufferBusyWaitWriteCompleteWaitBufferExterminateBufferCacheRedoLibCacheBufferCacheIOLocksNetworkREDOLogFilesDataFilesDBWRLGWRUser2User1User3LogBufferBufferCacheLogBufferBufferCach

2、eSGALibraryCacheOracleMemoryStructuresBufferCacheAccessBufferCacheManagementLocatingFreeblocksFindingdatablocksManagingLRUlistsCleaningDirtyBlocksBufferCachemanagementcancausecontentionDifferentfromIO(readingblocksofdisk)Query0.ParsestatementFindobjectinformationindatadictionaryCalculateexecutio

3、nplanIffulltablescanLookatallblocksoftableIfindexfindrootofindexandfollowtokeyDataDictionarywillhaveinfoabouttableorindexblockFile#Block#OnceyouknowtheblockDBA(file#+block#)…Selectenamefromempwhereempno=12;IsBlockincache?Nowyouhaveafile#andblock#Howdoyouknowifablockiscached?ShadowProcess?Doyouse

4、archalltheblocks?Couldbe1000sofblockstosearch.BuffercachesareinthemultiGigBufferCacheFindablockby:1)HashofDatafile#Block#2)Result=Bucket#3)Searchlinkedlistforthatbucket#WhatisahashvalueWhatareBucketsWhatisthelinkedlist?ConceptsTounderstandcontentiononthebuffercache,needtounderstand:LinkedListsHa

5、shingBucketsDoubleLinkedLists03C3900003C3947803C38F6003C3900003C3900003C38F6003C39478AddressNextPreviousHashingFunctionSimplehashcouldbeaModfunction1mod4=12mod4=23mod4=34mod4=05mod4=16mod4=27mod4=38mod4=0Using“mod4”asahashfuntioncreates4“buckets”tostorethingsHashBucketFillDataBlock1203HashBlock’

6、sfile#block#’sResultinabucket#PutBlockinbucket????HashBlock’s1file#437block#’s(1+437)mod4=2AfterawhilethebucketsbecomepopulatedwithblocksLatchesProtectBucketContentsBufferHeadersDataBlocksHashbucketlatchesBufferHeaderscontentsdescribedbyX$BHX$bhDescribesContentsofBufferHeadersSQL>descx$bhNameTyp

7、e--------------------ADDRRAW(4)DBARFILNUMBERDBABLKNUMBEROBJNUMBERHLADDRRAW(4)NXT_HASHRAW(4)PRV_HASHRAW(4)…muchmoreADDRDBARFILDBABLKOBJHLADDRNXT_HASHPRV_HASH…AeachbufferheadercontainsInformationaboutthedatablockItpointstoandt