3.模式对象管理概述(自学)

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1、SRC:Oracle8iAdministrator'sGuide(12)GuidelinesforManagingSchemaObjects·ManagingSpaceinDataBlocks·TransactionEntrySettings(INITRANSandMAXTRANS)·SettingStorageParameters·DeallocatingSpaceManagingSpaceinDataBlocksThePCTFREEandPCTUSEDparametersareusedto:1.Increas

2、etheperformanceofwritingandretrievingdata2.Decreasetheamountofunusedspaceindatablocks3.DecreasetheamountofrowchainingbetweendatablocksThePCTFREEParameterlThePCTFREEparameterisusedtosetthepercentageofablocktobereservedforpossibleupdatestorowsthatalreadyarecont

3、ainedinthatblock.lNoticethatbeforetheblockreachesPCTFREE,thefreespaceofthe24datablockisfilledbyboththeinsertionofnewrowsandbythegrowthofthedatablockheader.SpecifyingPCTFREElThedefaultforPCTFREEis10percent.Youcanuseanyintegerbetween0and99,inclusive,aslongasthe

4、sumofPCTFREEandPCTUSEDdoesnotexceed100.lAsmallerPCTFREEhasthefollowingeffects:1.Reserveslessroomforupdatestoexpandexistingtablerows2.Allowsinsertstofilltheblockmorecompletely3.Maysavespace,becausethetotaldataforatableorindexisstoredinfewerblocks(morerowsorent

5、riesperblock)lAlargerPCTFREEhasthefollowingeffects:1.Reservesmoreroomforfutureupdatestoexistingtablerows2.Mayrequiremoreblocksforthesameamountofinserteddata(insertingfewerrowsperblock)3.Mayimproveupdateperformance,becauseOracledoesnotneedtochainrowpiecesasfre

6、quently,ifeverlPCTFREEforNonclusteredTables:Ifthedataintherowsofanonclusteredtableislikelytoincreaseinsizeovertime,reservesomespacefortheseupdates.Otherwise,updatedrowsarelikelytobechainedamongblocks.lPCTFREEforClusteredTables:Thediscussionfornonclusteredtabl

7、esalsoappliestoclusteredtables.However,ifPCTFREEisreached,newrowsfromanytablecontainedinthesameclusterkeygointoanewdatablockthatischainedtotheexistingclusterkey.lPCTFREEforIndexes:YoucanspecifyPCTFREEonlywheninitiallycreatinganindex.ThePCTUSEDParameterlAftera

8、datablockbecomesfullasdeterminedbyPCTFREE,OracledoesnotconsidertheblockfortheinsertionofnewrowsuntilthepercentageoftheblockbeingusedfallsbelowtheparameterPCTUSED.24SpecifyingPCTUSEDlThede