浙江大学数据库系统概念PPT第十七章

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1、Chapter17:RecoverySystemFailureClassificationTransactionStateAquickviewofLog-BasedRecoveryFailureClassificationTransactionfailure:Logicalerrors:transactioncannotcompleteduetosomeinternalerrorconditionSystemerrors:thedatabasesystemmustterminateanactivetransactionduetoanerrorconditio

2、n(e.g.,deadlock)Systemcrash:apowerfailureorotherhardwareorsoftwarefailurecausesthesystemtocrash.Fail-stopassumption:non-volatilestoragecontentsareassumedtonotbecorruptedbysystemcrashDatabasesystemshavenumerousintegritycheckstopreventcorruptionofdiskdataDiskfailure:aheadcrashorsimil

3、ardiskfailuredestroysallorpartofdiskstorageDestructionisassumedtobedetectable:diskdrivesusechecksumstodetectfailuresRecoveryAlgorithmsRecoveryalgorithmsaretechniquestoensuredatabaseconsistencyandtransactionatomicityanddurabilitydespitefailuresRecoveryalgorithmshavetwopartsActionsta

4、kenduringnormaltransactionprocessingtoensureenoughinformationexiststorecoverfromfailuresActionstakenafterafailuretorecoverthedatabasecontentstoastatethatensuresatomicity,consistencyanddurabilityTransactionStateSinglestepTransactionState(Cont.)Active,theinitialstate;thetransactionst

5、aysinthisstatewhileitisexecutingPartiallycommitted,afterthefinalstatementhasbeenexecuted.Failed,afterthediscoverythatnormalexecutioncannolongerproceed.Aborted,afterthetransactionhasbeenrolledbackandthedatabaserestoredtoitsstatepriortothestartofthetransaction.Twooptionsafterithasbee

6、naborted:restartthetransaction–onlyifnointernallogicalerrorkillthetransactionCommitted,aftersuccessfulcompletion.ImplementationofAtomicityandDurabilityTherecovery-managementcomponentofadatabasesystemimplementsthesupportforatomicityanddurability.Theshadow-databasescheme:assumethaton

7、lyonetransactionisactiveatatime.apointercalleddb_pointeralwayspointstothecurrentconsistentcopyofthedatabase.allupdatesaremadeonashadowcopyofthedatabase,anddb_pointerismadetopointtotheupdatedshadowcopyonlyafterthetransactionreachespartialcommitandallupdatedpageshavebeenflushedtodisk

8、.incasetransactionfails,ol