fault tolerance

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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