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.Increasetheperformance

2、ofwritingandretrievingdata2.Decreasetheamountofunusedspaceindatablocks3.DecreasetheamountofrowchainingbetweendatablocksThePCTFREEParameterlThePCTFREEparameterisusedtosetthepercentageofablocktobereservedforpossibleupdatestorowsthatalreadyarecontainedinthatblock.lNoticethatbe

3、foretheblockreachesPCTFREE,thefreespaceofthe24datablockisfilledbyboththeinsertionofnewrowsandbythegrowthofthedatablockheader.SpecifyingPCTFREElThedefaultforPCTFREEis10percent.Youcanuseanyintegerbetween0and99,inclusive,aslongasthesumofPCTFREEandPCTUSEDdoesnotexceed100.lAsmal

4、lerPCTFREEhasthefollowingeffects:1.Reserveslessroomforupdatestoexpandexistingtablerows2.Allowsinsertstofilltheblockmorecompletely3.Maysavespace,becausethetotaldataforatableorindexisstoredinfewerblocks(morerowsorentriesperblock)lAlargerPCTFREEhasthefollowingeffects:1.Reserve

5、smoreroomforfutureupdatestoexistingtablerows2.Mayrequiremoreblocksforthesameamountofinserteddata(insertingfewerrowsperblock)3.Mayimproveupdateperformance,becauseOracledoesnotneedtochainrowpiecesasfrequently,ifeverlPCTFREEforNonclusteredTables:Ifthedataintherowsofanoncluster

6、edtableislikelytoincreaseinsizeovertime,reservesomespacefortheseupdates.Otherwise,updatedrowsarelikelytobechainedamongblocks.lPCTFREEforClusteredTables:Thediscussionfornonclusteredtablesalsoappliestoclusteredtables.However,ifPCTFREEisreached,newrowsfromanytablecontainedinth

7、esameclusterkeygointoanewdatablockthatischainedtotheexistingclusterkey.lPCTFREEforIndexes:YoucanspecifyPCTFREEonlywheninitiallycreatinganindex.ThePCTUSEDParameterlAfteradatablockbecomesfullasdeterminedbyPCTFREE,Oracledoesnotconsidertheblockfortheinsertionofnewrowsuntilthepe

8、rcentageoftheblockbeingusedfallsbelowtheparameterPCTUSED.24SpecifyingPCTUSEDlThede