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1、ASE126OpeningYourMaintenanceWindowKevinSherlock–StaffSystemsAnalyst,DexMediaInc.kevin.sherlock@teamsybase.comEricMiner-SeniorEngineer,SybaseInc.eric.miner@sybase.comAugust2003MakingUpdateStatisticsRunFasterFromtuningtheservertousinganewfeatureWe’lltalka
2、boutASE12.5.0.3’snewfeature‘SamplingforUpdateStatistics”We’llshowyousomesimplethingsyoucandonowtohelpspeedupupdatestatisticsAllofthesearedesignedtohelpmakeyourstatisticsmaintenanceeasierandmoreefficientWaystomakeitmoreefficientwhenyouhavetorunitShrinkin
3、gMaintenanceWindowsAsdatasetshavegrownsohasthetimeittakestorunupdatestatisticsInsomecasesthemaintenancewindowsimplyisn’tbigenoughtorunupdatestatisticswhetherit’sneededornotYourstatisticsmaintenanceneedstobeasefficientaspossibletomakethebestuseofyourwind
4、owYouwanttokeepyourstatisticsuptodatebutit’snexttoimpossibletodoinsomecasesHowcanyouspeedupupdatestatistics?Mymaintenancewindowisn’tbigenoughtorunupdatestatistics!Whatarethe‘Statistics’?Theoptimizeriscostbased–itneedstoknowabouttables.IndexesandthedataT
5、heoptimizermakesitsdecisionsbasedontheestimatedcostofagivenaccessmethodThestatisticsareusedtoestimatevariousselectivityvaluesTheselectivityvaluesareusedtoestimatethecostofagivenaccessmethodThestatisticsaretheoptimizer’sonlyviewofyourobjectsanddataWithou
6、tstatisticstheoptimizercanonlymakeguessesabouttheobjectsanddataAndwhydoweneedthem?ThereAreTwoTypesofStatisticsTable/Indexlevel-describesatableanditsindex(es)Data&Leafpagecount,Data&Leafrowcount,Emptydata&leafpagecount,Forwardedrowcount,Deletedrowcount,O
7、AM&allocationpage,Firstextentleafpages,Data/Leafrowsize,Indexheight,Data/Indexpageclusterratio,DataRowclusterratioSomevaluesareupdateddynamicallyasDMLoccursPage&rowcounts,deletedrows,forwardedrows,clusterratiosTheothervaluesarestaticandupdatedbyupdatest
8、atisticsSpaceUtilization,LargeI/OEfficiencyareNOTusedbyoptimizer.They’reForyourinformationonly–helpstrackfragmentationCannotbewrittendirectlyorwithoptdiag–quicklyoverwrittenStoredinsystabstatsColumnlevel-describesthedatatotheopti
