Oracle 10G DataGuard Real Time ApplyFlashback Database features.docx
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Oracle 10G DataGuard Real Time ApplyFlashback Database features.docx
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Oracle10GDataGuardRealTimeApplyFlashbackDatabasefeatures
Oracle10GDataGuardRealTimeApply&FlashbackDatabaseFeatures–AnImplementationExperience
TJMitra
DatacomSystemsLimited
NZOUG2007Presentation
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TheBackground
MyrecentprojectinvolvesupgradingoneofourClient’sBankingdatabasesfromOracleversion9iRelease9.2toOracleversion10GRelease10.2.
ThePre-ProductionenvironmenthasPrimaryandStandbyDatabaseshostedondifferentSolarisServersgeographicallylocatedintwoseparatecities.
Thispapertriestoanalyse&discussvarioushighavailabilityaspectsaroundOracle10GR2DataGuardandusageofFlashbackDatabasefeatures.
AnalysisoftheCurrentenvironment
∙BecauseoftheBankingenvironment,thehighavailability&theintegrityoftheDataareofmandatoryrequirements
∙CurrentlytheOracleversionisOracle9.2.0.6.0
∙DataGuardenvironmentisPhysicalStandby
∙LogTransportfromPrimarytoStandbyhappensusingArchiver(ARCH),notLogWriter(LGWR)
∙StandbyModeisMaximumPerformance
∙NetworkTransmissionModeisASYNC
∙TheRedoLogSizesare512KB
∙LogshippinghappensonlywhenthePrimaryRedoLogfillsupandswitches
∙ThisDataGuardversiondoesn’tsupportReal-TimeApplybutusesRedoApply
∙RedoApplymeansRedogeneratedatPrimaryisappliedtoStandbyonlywhenthereisalogswitchatthePrimary
∙ThereisnoAutomaticApplyDelaysetintheStandbymeaningassoonasArchiveLogarrivesattheStandbyhost,itgetsappliedontotheStandbydatabase
∙OperationsMenuhasanoptiontodisabletheLogApplytotheStandbywhendesired,thatwillstopStandbyfollowingPrimary
∙BecauseofthesmallersizeoftheRedoLogs,veryfrequentlogswitcheshavebeenobservedduringBatchRuns
∙Thereisnoflashbackmechanismavailableinthecurrentsystem
∙FlashbackisanOracleRDBMS10GTechnologyfeaturewhichallowsdatabasetoberewoundbackinthepastbasedonTimeStamporSystemChangeNumber(SCN)oradefinedRestorepoint
∙UsingOracleDataGuardRoleTransitionServicescommandsembeddedintheOperationsMenu,Switchover&SwitchbackhappensbetweenPrimary&StandbySitesatregularmonthintervals
∙CapabilityofFailovertotheStandbyDatabaseafteraPrimaryfailurehasbeenbuiltintotheOperationsMenu
FollowingwerethespecialconsiderationswhentheCurrentSystemwasdesigned:
∙OracleRedoLogsizewaschosenas512ktobecompatiblewiththethenavailableNetworkBandwidth&Latencyandalsotominimizetheriskofdataloss
∙StandbyModewaschosenasMaximumPerformance
∙BecauseredotransmissionhappenedovertheWideAreaNetwork(WAN),MaximumProtectionmodewasnotchosenasitneededhighlyreliablenetworkwithlowlatency,highbandwidth,resilienceandredundancy
∙InMaximumProtectionmode,redoisnotcommittedonPrimaryunlessitisalsocommittedonStandby,sothatcouldhavenegativeperformanceimpactonthePrimaryifredotransmissionoverslowWANcausesRedoApplyonStandbytobecomeslow
∙Also,inMaximumProtectionmodeiftheStandbyisshutdownthatwillcausePrimarytoshutdown
FollowingaretherequirementsfortheApplication
∙Data/TransactionLossshouldbeminimumincaseofaFailovertoStandbyfollowingPrimaryfailure
∙ThereshouldbenoperformanceimpactonthePrimaryduringLogShipping
∙PrimarymustnotshutdownforanyRedoTransportorRedoApplyproblem
∙TherewillnotbeanyRedoLogApplyDelayontheStandby
∙TheStandbyshouldtrytofollowthePrimaryascloselyaspossible
∙But,atthesametime,itshouldbepossibletostoptheLogApplyonStandbywhenandifdesiredorrequired
∙IfthePrimaryisrewoundintime,thentheStandbyalsoshouldberewoundtothesamepointintime.
∙E.g.ifthereisanyprobleminthePrimarydatabasee.g.failedBatch,thenthroughMenuoption,OperationsSupportshouldbeabletorewindboththePrimary&Standbydatabasesbackintothepasttothepointintimejustbeforetheproblemhashappened
∙CapabilityofAlternateSiteSwitchover&SwitchbackusingOracleDataGuardRoleTransitionServicesmustcontinuetobeavailable
∙CapabilityofFailovertotheStandbyDatabaseafteraPrimaryfailuremustcontinuetobeavailable
∙Asfutureenhancement,thepossibilityofusingtheDRdatabaseasReportingServeristobeexplored
ProposedEnhancements
Toaddresstheabovementionedrequirements,thefollowingOracle10Gfeatureswereexplored:
∙ManagedRecoveryofthePhysicalStandbyinRealTimeApplymodetominimiseDataLossontheStandbyintheeventofPrimaryfailure
∙ImplementationofFlashbackdatabasefeatureinbothPrimary&Standbyintroducingthecapabilityofrewindingboththedatabasestoadefinedstateinthepastwithoutgoingthroughtime-consumingMediaRestore&RecoveryProcess
OracleRDBMSVersion
∙OracleRDBMS10Gwillbeused
∙InitiallyOracle10GR1waschosen,butbecauseoffewbugs(fewmentionedbelow)ithasbeendecidedOracle10GR2istobeused
∙AsPatchRelease10.2.0.3hasaddressedfixesaroundflashback,thispatchreleaseistobeused
∙CurrentOracle10GPatchversionontheServersis10.2.0.2,soallOracleServersstartingfromDevelopmenttoUATtoPre-ProductionwillbepatchedtoOracle10.2.0.3
∙OracleCriticalPatchreleasedasofJanuary2007willbeappliedonallOracleServers
DataGuardEnvironment
∙TheDataGuardEnvironmentwillcontinuetoremainPhysicalStandby
∙AsthePrimary/StandbyPairoperatesoveraWideAreaNetworkandalsoasofotheroperationalissues,Oracle10GDataGuardStandbyModewillremainMaximumPerformance,thoughpossibilityofusingMaximumProtectionmodecouldbeexplored
∙LogTransportfromPrimarytoStandbywillhappenusingLogWriternotArchiver
∙LGWRASYNCLNSBufferwassetto50MBasavailableinOracle10GR1(10MBinOracle9i).InOracle10GR2,asfurtherenhancementLNSprocess,insteadofreadingfromin-memorybuffer,readsfromPrimaryonlineredolog,soisnotconstrainedtoin-memorybufferfillingupsituation.Also,Net_timeoutattributeisnotneededinLog_archive_dest_2parameterasfromOracle10.2,LGWRneverwaitsforLNS.
∙SendDataUnit(SDU)willbesetto32kforoptimumperformanceofSqlnet
WANimprovement
∙WANperformancehasbeenimprovedbyfivefold.ThiswaspossiblebyupgradingallthenetworkgearsandincreasedWANbandwidth.Additionalcarrierswereaddedforredundancy
Oracle10GDataGuardStandbyReal-TimeApply
∙OracleDataGuard10GStandbyReal-TimeApplymechanismwillbeused
∙RealTimeApplywilluseLGWRonthePrimarytowriteredodatatoStandbyRedologontheStandbyandLogApplyServicescanapplytheredodatainreal-timewithouttheneedofthecurrentstandbyredologbeingarchived
∙InRealTimeApply,onceatransactioniscommittedonthePrimary,thecommittedchangeswillbeavailableontheStandbyinRealTimeevenwithoutswitchingthelogatthePrimary
∙OperationsMenuwillcontinuetohavetheoptiontodisabletheLogApplytoStandbywhendesired,thatwillstopStandbyfollowingPrimary
∙BecauseoftheReal-TimeApply,theDatabaseOn-lineRedoLogSizescanbeincreasedto20MBeachassuggestedbyOracle10GRDBMSAdvisorduringtestBatchRuns.Thiswillabsorbfrequentlogswitchesduringbatchruns
∙ForgoodReal-TimeApplyPerformance,OraclesuggestsWideAreaNetwork(WAN)ReturnTripTime(RTT)toremainbelow100ms
∙CurrentWANRTT,evenduringmostactiveBatchPeriod,hasbeenobservedtobeintherangeof15-20ms,wellbelowthecriticalrange
∙AcallwasloggedwithOracletoconfirmthatOracle10GDataGuardReal-TimeApplydoesn’tintroduceanycorruptionofData
∙OracleCorporationhasconfirmed,asofnow,forusageofthisfeaturenobughasbeenobservedwhichcouldpotentiallyleadtoDataCorruption
Oracle10GFlashbackDatabaseFeature
∙Oracle10GFlashbackDatabasefeaturewillbeenabledonbothPrimary&Standby
∙Flashbackingcapabilitywillbedefinedfor5days
∙Also,NamedRestorePoints,asavailableinOracle10GR2,willbeused
∙TheRestorePointswillbecreatedwith‘guaranteeflashbackdatabase’option
∙OperationsMenuwillhaveoptiontomanuallyregisterRestorepointsforflashback
∙MenuwillhaveoptiontodisplaytheRestorepoints&thetimeeachRestorepointthedatabasecanflashbackto
∙MenuwillhaveoptiontoissuecommandtoflashbackthedatabasetoadesiredRestorePoint
∙Menuwillhaveoptiontodropold&obsoleteRestorePoints
∙ForBatchApplication,therewillbeanamedRestorePointcalled‘PreBatch’automaticallydroppedandre-createdfromwithintheApplicationatthebeginningoftheBatcheveryday.
∙IncaseofBatchfailure,insteadofaDBACallout,usingMenu,OperationsSupportwillFlashbackthedatabasetotheRestorePoint‘PreBatch’
∙Currentlytorecoverfromthatscenario,aDBAcalloutisnecessaryandwouldtakeaboutapproximate3-4hourstorecovertheDatabasefromtheBackup
∙Also,currentlyafteraFailover,DBAneedstorebuildtheoriginalPrimaryasthecurrentStandbyfromamostrecentbackupofthenewPrimary
∙IfFlashbackfeatureisenabled,thenthislengthyprocedurecanbeavoidedbecauseaFlashbackenabledPrimarydatabasecanbeeasilyrewoundtoaconsistentpointandthenbemadeasnewStandbyandstartreceiving&applyinglogsfromthenewPrimary
∙AnothercallwasloggedwithOracletoconfirmthatOracle10GFlashbackDatabasefeaturedoesn’tintroduceanycorruptionofData
∙OracleCorporationhasconfirmed,asofnow,fortheusageofthisfeaturenobug
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