吉林大学大型数据库设计与实现dba-10.ppt

ManagingUndoData

ObjectivesAftercompletingthislesson,youshouldbeabletodothefollowing:DescribethepurposeofundodataImplementAutomaticUndoManagementCreateandconfigureundosegmentsObtainundosegmentinformationfromthedatadictionary

ManagingUndoDataOverviewTwomethodsformanagingundodataexistsAutomaticUndoManagementManualUndoManagementThislessondiscussesAutomaticUndoManagementThetermundoreplaceswhatwasknowninpreviousversionsofOracleasrollback

UndoSegmentUpdatetransactionOldimageNewimageUndosegmentTable

UndoSegments:PurposeTransactionrollbackTransactionrecoveryUndosegmentReadconsistency

ReadConsistencyImageatstartofstatementNewimageTableSELECT*

FROMtable

TypesofUndoSegmentsSYSTEM:UsedforobjectsintheSYSTEMtablespaceNon-SYSTEM:Usedforobjectsinothertablespaces:AutoMode:RequiresanUNDOtablespaceManualMode:Private:AcquiredbyasingleinstancePublic:AcquiredbyanyinstanceDeferred:Usedwhentablespacesaretakenofflineimmediate,temporary,orforrecovery

AutomaticUndoManagement:

ConceptsUndodataismanagedusinganUNDOtablespaceYouallocateoneUNDOtablespaceperinstancewithenoughspacefortheworkloadoftheinstance.TheOracleserverautomaticallymaintainsundodatawithintheUNDOtablespace.

AutomaticUndoManagement:

ConfigurationConfiguretwoparametersintheinitializationfile:UNDO_MANAGEMENTUNDO_TABLESPACECreateatleastoneUNDOtablespace.Initializationfileundo1db01.dbfUNDOTablespace

AutomaticUndoManagement:

InitializationParametersUNDO_MANAGEMENT:SpecifieswhetherthesystemshoulduseAUTOorMANUALmode.UNDO_TABLESPACE:SpecifiesaparticularUNDOtablespacetobeused.UNDO_MANAGEMENT=AUTOUNDO_TABLESPACE=UNDOTBS

AutomaticUndoManagement:

UNDOTablespaceYoumaycreatetheUNDOtablespacewiththedatabasebyaddingaclauseintheCREATEDATABASEcommandOrcreateitlaterbyusingtheCREATEUNDOTABLESPACEcommandCREATEDATABASEdb01...U