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1、Module12FaultToleranceFaultTolerance03-200312-1?2001,2003InternationalBusinessMachinesCorporationObjectivesAttheendofthismodule,youwillbeableto:?Describethetypesoffailuresthatcouldoccurontheserversystem?Describethefastrecoveryprocess?Examinethestatusofchunksanddbspaces?Identifytheconfigurat
2、ionparametersassociatedwithrecovery12-212-2FaultToleranceTypesofSystemFailures￠Systemcrash—Theentirecomputersystemgoesdown￠Disk—Adiskthatcontainspartofthedatabaseserverdatabecomesunusable￠Systemfailure—Thecomputersystemandthedisksassociatedwithitbecomeunusable,orthedatawithintheserverbecome
3、scorruptedMechanismstheserverusestorecover:?Fastrecovery?Diskmirroring?Restorefromarchive?Datareplication12-3Theserverusesseveralmechanismsforsystemrecovery:fastrecovery,restoringfromanarchive,diskmirroringanddatareplication.Herearesometypesofsystemfailuresthatcouldoccur:￠Systemcrash—Ifthec
4、omputersystemgoesdownbecauseofapowerfailureorsomeotherreason,thedatabaseservermustquicklyrecovertoaconsistentstateonceyourestartthecomputersystem.Fastrecoveryisusedforthispurpose.￠Diskcrash—Ifadiskthatcontainsserverdatabecomesunusableforanyreason,theremustbeamethodtorecoverthedataonthatdisk
5、toaconsistentstate.Youcanrestorefromanarchiveandrollforwardlogicallogstoreturnthesystemtothestateitwasinwhenthediskbecameunusable.Ifadiskismirrored,however,theservercontinuesandisunaffectedifthediskfailsforanyreason.￠Systemfailure—Intheeventofacompletesystemfailure,datareplicationprovidesas
6、econdarydatabaseserverasanimmediately-availablebackupsystem.FaultTolerance12-3WhatisFastRecovery?Fastrecoveryisanautomatic,fault-tolerancefeaturethattheserverexecutesanytimetheoperatingmodechangesfromofflinetoquiescentmode.Fastrecoveryattainstwogoals:?Thephysicallogisusedtoreturntheserverto
7、themostrecentpointofknownphysicalconsistency:themostrecentcheckpoint?Thelogicallogsareusedtoreturntheservertologicalconsistencybyrollingforwardalltransactionsthathaveoccurredsincethecheckpoint,androllingbackalltransactionsthatareuncommitted12-4Fastrecove
