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.Increasetheperforman

2、ceofwritingandretrievingdata2.Decreasetheamountofunusedspaceindatablocks3.DecreasetheamountofrowchainingbetweendatablocksThePCTFREEParameterlThePCTFREEparameterisusedtosetthepercentageofablocktobereservedforpossibleupdatestorowsthatalreadyarecontainedinthatblock.lNoticeth

3、atbeforetheblockreachesPCTFREE,thefreespaceofthe24datablockisfilledbyboththeinsertionofnewrowsandbythegrowthofthedatablockheader.SpecifyingPCTFREElThedefaultforPCTFREEis10percent.Youcanuseanyintegerbetween0and99,inclusive,aslongasthesumofPCTFREEandPCTUSEDdoesnotexceed100.

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

5、.Reservesmoreroomforfutureupdatestoexistingtablerows2.Mayrequiremoreblocksforthesameamountofinserteddata(insertingfewerrowsperblock)3.Mayimproveupdateperformance,becauseOracledoesnotneedtochainrowpiecesasfrequently,ifeverlPCTFREEforNonclusteredTables:Ifthedataintherowsofa

6、nonclusteredtableislikelytoincreaseinsizeovertime,reservesomespacefortheseupdates.Otherwise,updatedrowsarelikelytobechainedamongblocks.lPCTFREEforClusteredTables:Thediscussionfornonclusteredtablesalsoappliestoclusteredtables.However,ifPCTFREEisreached,newrowsfromanytablec

7、ontainedinthesameclusterkeygointoanewdatablockthatischainedtotheexistingclusterkey.lPCTFREEforIndexes:YoucanspecifyPCTFREEonlywheninitiallycreatinganindex.ThePCTUSEDParameterlAfteradatablockbecomesfullasdeterminedbyPCTFREE,Oracledoesnotconsidertheblockfortheinsertionofnew

8、rowsuntilthepercentageoftheblockbeingusedfallsbelowtheparameterPCTUSED.24SpecifyingPCTUSEDlThede