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DatabaseBackupandRecoveryUser'sGuide

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21()TuningRMANPerformanceThischaptercontainsthefollowingsections:

PurposeofRMANPerformanceTuning

BasicConceptsofRMANPerformanceTuning

UsingV$ViewstoDiagnoseRMANPerformanceProblems

TuningRMANBackupPerformance

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()PurposeofRMANPerformanceTuning

(//docs.oracle.com/en/) WelcomeDAVID

AnRMANbackuporrestorejobcanbedividedintoseparatephasesorcomponents.TheslowestofthesephasesinanyRMANjobiscalledthebottleneck.ThepurposeofRMANtuningistoidentifythebottlenecksforagivenjobanduseRMANcommands,initializationparameters,oradjustmentstophysicalmediatoimproveperformance.

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()BasicConceptsofRMANPerformanceTuningTuningRMANperformancerequiresadetailedunderstandingofhowRMANcreatesabackup.Asexplainedin"RMANChannels"(rcmarchi.htm#i1012864),theworkofabackupisperformedbyoneormorechannels.Achannel(glossary.htm#i432240)representsastreamofbytestoastoragedevice.

Forthepurposesofillustration,youcanthinkofthebytestreamaspassingfromtheinputbuffersinmemorythroughtheCPUtotheoutputbuffers,andfromtheretothestoragedevice.Todirectabackuptotwotapedevices,youallocatetwotapechannelssothateachbytestreamgoestoadifferentdevice.

Theworkofeachchannel,whetheroftypediskorSBT,issubdividedintothefollowingdistinctphases:

ReadPhase

AchannelreadsblocksfromdiskintoinputI/Obuffers.

CopyPhase

Achannelcopiesblocksfrominputbufferstooutputbuffersandperformsadditionalprocessingontheblocks.

WritePhase

Achannelwritestheblocksfromoutputbufferstostoragemedia.Thewritephasecantakeeitherofthefollowingmutuallyexclusiveforms,dependingonthetypeofbackupmedia:

WritePhaseforSBT

2. WritePhaseforDisk

Figure211depictstwochannelsbackingupdatastoredonthreedisks.Eachchannelreadsthedataintotheinputbuffers,processesthedatawhilecopyingitfromtheinputtotheoutputbuffers,andthewritesthedatafromtheoutputbufferstodisk.

()Figure211PhasesofaMultichannelBackuptoDisk

Descriptionof"Figure211PhasesofaMultichannelBackuptoDisk"(img_text/bradv042.htm)

Figure212alsodepictstwochannelsbackingupdatastoredonthreedisks,butoneofthedisksismountedremotelyoverthenetwork.Eachchannelreadsthedataintotheinputbuffers,processesthedatawhilecopyingitfromtheinputtotheoutputbuffers,andthewritesthedatafromtheoutputbuffersto

tape.Channel1writesthedatatoalocallyattachedtapedrive,whereaschannel2sendsthedataoverthenetworktoaremotemediaserver.

()Figure212PhasesofaMultichannelBackuptoTape

Descriptionof"Figure212PhasesofaMultichannelBackuptoTape"(img_text/bradv041.htm)

Whenrestoringdata,achannelperformsthesestepsinreverseorderandreversesthereadingandwritingoperations.ThefollowingsectionsexplainRMANtuningconceptsintermsofabackup.

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()ReadPhaseThissectionexplainsfactorsthataffectperformancewhenanRMANchannelisreadingdatafromdisk:

AllocationofInputDiskBuffers

SynchronousandAsynchronousDiskI/O

DiskI/OSlaves

RATEChannelParameter

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()AllocationofInputDiskBuffersDuringabackup,anRMANchannelreadstheblocksfromtheinputfilesintoI/Odiskbuffers.ThedatabasefilesonthedisksubsystemcanbemanagedbyeitherAutomaticStorageManagement(ASM)(glossary.htm#CHDBDJIJ)oranalternativevolumemanagerorfilesystem.TheconsiderationsforbackuptuningchangedependingonwhetheryoumanagedatabasefileswithASM.

Theallocationoftheinputbuffersdependsonhowthefilesaremultiplexed.()()Backupmultiplexing(glossary.htm#i999499)isRMAN'sabilitytoreadanumberoffilesinabackupsimultaneouslyfromdifferentsourcesandthenwritethemtoasinglebackuppiece.Thelevelofmultiplexing(glossary.htm#CHDFBDDG),whichisthenumberofinputfilessimultaneouslyreadandthenwrittenintothesamebackuppiece(glossary.htm#i432114),isdeterminedbythealgorithmdescribedin"MultiplexedBackupSets"(rcmcncpt.htm#i1015964).Reviewthissectionbeforeproceeding.

WhenanRMANchannelbacksupfilesfromdisk,itusestherulesdescribedinthefollowingtabletodeterminehowlargetomaketheinputdiskbuffers.

()()Table211DatafileReadBufferSizingAlgorithm

LevelofMultiplexing InputDiskBufferSize

Lessthanorequalto4

TheRMANchannelallocates16buffersofsize1MBsothatthetotalbuffersizeforalltheinputfilesis16MB.

Greaterthan4butlessthanorequalto8

TheRMANchannelallocatesavariablenumberofdiskbuffersofsize512KBsothatthetotalbuffersizeforalltheinputfilesislessthan16MB.

Greaterthan8 TheRMANchannelallocates4diskbuffersof128KBforeachfile,sothatthetotalbuffersizeforeachinputfileis512KB.

IntheexampleshowninFigure213,onechannelisbackingupfourdatafiles.MAXOPENFILES issetto4andFILESPERSET issetto4.Thus,thelevelofmultiplexingis4.So,thetotalsizeofthebuffersforeachdatafileis4MB.Thecombinedsizeofallthebuffersis16MB.

()Figure213DiskBufferAllocation

Descriptionof"Figure213DiskBufferAllocation"(img_text/bradv011.htm)

IfachannelisbackingupfilesstoredinASM,thenthenumberofinputdiskbuffersequalsthenumberofphysicaldisksintheASMdiskgroup.Forexample,ifadatafileisstoredinanASMdiskgroupthatcontains16physicaldisks,thenthechannelallocates16inputbuffersforthedatafilebackup.

Ifachannelisrestoringabackupfromdisk,then4buffersareallocated.Thesizeofthebuffersisdependentontheoperatingsystem.

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()()SynchronousandAsynchronousDiskI/OWhenachannelreadsfromorwritestodisk,theI/OiseithersynchronousI/O(glossary.htm#CHDDCBGC)orasynchronousI/O(glossary.htm#CHDIIJAC).WhenthediskI/Oissynchronous,aserverprocesscanperformonlyonetaskatatime.WhenthediskI/Oisasynchronous,aserverprocesscanbeginanI/OandthenperformotherworkwhilewaitingfortheI/Otocomplete.RMANcanalsobeginmultipleI/Ooperationsbeforewaitingforthefirsttocomplete.

WhenreadingfromanASMdiskgroup(glossary.htm#CHDHIIBA),youshoulduseasynchronousdiskI/Oifpossible.Also,ifachannelreadsfromarawdevice(glossary.htm#CHDHBJAG)managedwithavolumemanager,thenasynchronousdiskI/Oalsoworkswell.SomeoperatingsystemssupportnativeasynchronousdiskI/O.Thedatabasetakesadvantageofthisfeatureifitisavailable.

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()()DiskI/OSlavesOnoperatingsystemsthatdonotsupportnativeasynchronousI/O,thedatabasecansimulateitwithspecialI/Oslaveprocesses.TheseprocessesarededicatedtoperformingI/Oonbehalfofanotherprocess.

YoucancontroldiskI/OslavesbysettingtheDBWR_IO_SLAVES initializationparameter,whichisnotdynamic.TheparameterspecifiesthenumberofI/Oserverprocessesusedbythedatabasewriterprocess(DBWR).Bydefault,thevalueis0andI/Oserverprocessesarenotused.IfasynchronousI/Oisdisabled,thenRMANallocatesfourbackupdiskI/OslavesforanynonzerovalueofDBWR_IO_SLAVES .

WhenattemptingtogetsharedbuffersforI/Oslaves,thedatabasedoesthefollowing:

IfLARGE_POOL_SIZE isset,andiftheDBWR_IO_SLAVES parameterissettoanonzerovalue,thenthedatabaseattemptstogetmemoryfromthelargepool.Ifthisvalueisnotlargeenough,thenanerrorisrecordedinthealertlog,thedatabasedoesnottrytogetbuffersfromthesharedpool,andasynchronousI/Oisnotused.

IfLARGE_POOL_SIZE isnotsetorissettozero,thenthedatabaseattemptstogetmemoryfromthesharedpool.

Ifthedatabasecannotgetenoughmemory,thenitobtainsI/ObuffermemoryfromthePGAandwritesamessagetothealert .log fileindicatingthatsynchronousI/Oisusedforthisbackup.

Thememoryfromthelargepoolisusedformanyfeatures,includingthesharedserver,parallelquery,andRMANI/Oslavebuffers.ConfiguringthelargepoolpreventsRMANfromcompetingwithothersubsystemsforthesamememory.

Requestsforcontiguousmemoryallocationsfromthesharedpoolareusuallysmall(under5KB)insize.However,itispossiblethatarequestforalargecontiguousmemoryallocationcaneitherfailorrequiresignificantmemoryhousekeepingtoreleasetherequiredamountofcontiguousmemory.Althoughthesharedpoolmaybeunabletosatisfythismemoryrequest,thelargepoolisabletodoso.Thelargepooldoesnothavealeastrecentlyused(LRU)listthedatabasedoesnotattempttoagememoryoutofthelargepool.

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()RATEChannelParameterIntheALLOCATE orCONFIGURECHANNEL commands,theRATE parameterspecifiesthebytes/secondthatarereadonachannel.YoucanusethisparametertosetanupperlimitforbytesreadsothatRMANdoesnotconsumeexcessivediskbandwidthanddegradeonlineperformance.Essentially,RATE servesasabackupthrottle.Forexample,ifyousetRATE1500K ,andifeachdiskdrivedelivers3MB/second,thenthechannelleavessomediskbandwidthavailabletotheonlinesystem.

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()CopyPhaseInthisphase,achannelcopiesblocksfromtheinputtotheoutputbuffersandperformsadditionalprocessing.Forexample,ifachannelreadsdatafromdiskandbacksuptotape,thenthechannelcopiesthedatafromthediskbufferstotheoutputtapebuffers.

Thecopyphaseinvolvesthefollowingtypesofprocessing:

Validation

Compression

Encryption

Whenperformingvalidation(glossary.htm#i433696)oftheblocks,RMANchecksthemforcorruption.ValidationisexplainedinChapter15,"ValidatingDatabaseFilesandBackups"(rcmvalid.htm#CHDBFAIF).Typically,thisprocessingisnotCPUintensive.

Whenperformingbinarycompression(glossary.htm#CHDEEEDG),RMANappliesacompressionalgorithmtothedatainbackupsets.BinarycompressioncanbeCPUintensive.YoucanchoosewhichcompressionalgorithmthatRMANusesforbackups.Bydefault,RMANusesBZIP2 ,whichhasaverygoodcompressionratio.ZLIB compression,whichrequiresaCOMPATIBLE settingof11.0.0orhigher,isveryfastbuthasalowercompressionratiothanotheralgorithms.Binarycompressionisexplainedin"MakingCompressedBackups"(rcmbckba.htm#i1034440).

Whenperformingbackupencryption(glossary.htm#CHDJDIEJ),RMANencryptsbackupsetsbyusingoneofthealgorithmslisted()inV$RMAN_ENCRYPTION_ALGORITHMS .RMANoffersthreemodesofencryption:transparent,passwordprotected,anddualmode.Backupencryptionisexplainedin"EncryptingRMANBackups"(rcmbckad.htm#CEGEJABH).BackupencryptioncanbeCPUintensive.

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()WritePhaseforSBTWhenbackinguptoSBT,RMANgivesthemediamanager(glossary.htm#i432922)astreamofbytesandassociatesauniquenamewiththisstream.Alldetailsofhowandwherethatstreamisstoredarehandledentirelybythemediamanager.Thus,abackuptotapeinvolvestheinteractionofbothRMANandthemediamanager.

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()RMANComponentofWritePhaseforSBTTheRMANspecificfactorsaffectingtheSBTwritephaseareanalogoustothefactorsaffectingdiskreads.Inbothcases,thebufferallocation,slaveprocesses,andsynchronousorasynchronousI/Oaffectperformance.

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()()AllocationofTapeBuffers

IfyoubackuptoorrestorefromanSBT(glossary.htm#CHDCCBFI)device,thenbydefaultthedatabaseallocatesfourbuffersforeachchannelforthetapewriters(orreadsifrestoringdata).ThesizeofthetapeI/Obuffersisplatformdependent.YoucanchangethisvaluewiththePARMS andBLKSIZE parametersoftheALLOCATECHANNEL orCONFIGURECHANNEL command.

()Figure214AllocationofTapeBuffers

Descriptionof"Figure214AllocationofTapeBuffers"(img_text/bradv013.htm)

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()TapeI/OSlaves

RMANallocatesthetapebuffersintheSGAorthePGA,dependingonwhetherI/Oslavesareused.IfyousettheinitializationparameterBACKUP_TAPE_IO_SLAVES=true ,thenRMANallocatestapebuffersfromtheSGA.Tapedevicescanonlybeaccessedbyoneprocessatatime,soRMANstartsasmanyslavesasnecessaryforthenumberoftapedevices.IftheLARGE_POOL_SIZE initializationparameterisalsoset,thenRMANallocatesbuffersfromthelargepool.IfyousetBACKUP_TAPE_IO_SLAVES=false ,thenRMANallocatesthebuffersfromthePGA.

IfyouuseI/Oslaves,thensettheLARGE_POOL_SIZE initializationparametertodedicateSGAmemorytoholdingtheselargememoryallocations.ThisparameterpreventsRMANI/ObuffersfromcompetingwiththelibrarycacheforSGAmemory.IfI/OslavesfortapeI/OwererequestedbutthereisnotenoughspaceintheSGAforthem,slavesarenotused,andamessageappearsinthealertlog.

NotethatBACKUP_TAPE_IO_SLAVES specifieswhetherRMANusesslaveprocesses,notthenumberofslaveprocesses.Tapedevicescanonlybeaccessedbyoneprocessatatime,andRMANusesthenumberofslavesnecessaryforthenumberoftapedevices.

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()()SynchronousandAsynchronousI/O

WhenanSBTchannelreadsorwritesdatatotape,theI/Oisalwayssynchronous.FortapeI/O,eachchannelallocated(whethermanuallyorautomatically)correspondstoaserverprocess,calledhereachannelprocess.

ThefollowingfigureshowssynchronousI/Oinabackuptotape.

()Figure215SynchronousTapeI/O

Descriptionof"Figure215SynchronousTapeI/O"(img_text/bradv015.htm)

Thefollowingstepsoccur:

Thechannelprocesscomposesatapebuffer.

Thechannelprocessexecutesmediamanagercodethatprocessesthetapebufferandinternalizesitforfurtherprocessingandstoragebythemediamanager.

Themediamanagercodereturnsamessagetotheserverprocessstatingthatithascompletedwriting.

Thechannelprocesscaninitiateanewtask.

ThefollowingfigureshowsasynchronousI/Oinatapebackup.AsynchronousI/Ototapeissimulatedbyusingtapeslaves.Inthiscase,eachallocatedchannelcorrespondstoaserverprocess,whichintheexplanationwhichfollowsisidentifiedasachannelprocess.Foreachchannelprocess,onetapeslaveisstarted(ormorethanone,inthecaseofmultiplecopies).

()Figure216AsynchronousTapeI/O

Descriptionof"Figure216AsynchronousTapeI/O"(img_text/bradv012.htm)

Thefollowingstepsoccur:

Achannelprocesswritesblockstoatapebuffer.

Thechannelprocesssendsamessagetothetapeslaveprocesstoprocessthetapebuffer.Thetapeslaveprocessexecutesmediamanagercodethatprocessesthetapebufferandinternalizesitsothatthemediamanagercanprocessit.

Whilethetapeslaveprocessiswriting,thechannelprocessisfreetoreaddatafromthedatafilesandpreparemoreoutputbuffers.

Afterthetapeslavechannelreturnsfromthemediamanagercode,itrequestsanewtapebuffer,whichusuallyisready.Thuswaitingtimeforthechannelprocessisreduced,andthebackupiscompletedfaster.

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()MediaManagerComponentofWritePhaseforSBTThefollowingfactorsaffectthespeedofthebackuptotape:

NetworkThroughput

NativeTransferRate

TapeCompression

TapeStreaming

PhysicalTapeBlockSize

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()NetworkThroughput

Ifthetapedeviceisremote,thenthemediamanagerneedstotransferdataoverthenetwork.Forexample,anadministrativedomaininOracleSecureBackupcancontainmultiplenetworkedclienthosts,mediaservers,andtapedevices.Ifthedatabaseisononehost,buttheoutputtapedriveisattachedtoadifferenthost,thenOracleSecureBackupmanagesthedatatransferoverthenetwork.Thenetworkthroughputistheupperlimitforbackupperformance.

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()NativeTransferRate

Thetapenativetransferrate(glossary.htm#CHDDDBEG)isthespeedofwritingtoatapewithoutcompression.Thisspeedrepresentstheupperlimitofthebackuprate.Theupperlimitofyourbackupperformanceshouldbetheaggregatetransferrateofallofyourtapedrives.Ifyourbackupisalreadyperformingatthatrate,andifitisnotusinganexcessiveamountofCPU,thenRMANperformancetuningwillnothelp.

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()TapeCompression

Theleveloftapecompressionisveryimportantforbackupperformance.Ifthetapehasgoodcompression,thenthesustainedbackuprateisfaster.Forexample,ifthecompressionratiois2:1andnativetransferrateofthetapedriveis6MB/s,thentheresultingbackupspeedis12MB/s.Inthiscase,RMANmustbeabletoreaddiskswithathroughputofmorethan12MB/sorthediskbecomesthebottleneckforthebackup.

Note:YoushouldnotusebothtapecompressionprovidedbythemediamanagerandbinarycompressionprovidedbyRMAN.Ifthemediamanagercompressionisefficient,thenitisusuallythebetterchoice.UsingRMANcompressedbackupsetscanbeaneffectivealternativetoreducebandwidthusedtomoveuncompressedbackupsetsoveranetworktothemediamanager,iftheCPUoverheadrequiredtocompressthedatainRMANisacceptable.

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()TapeStreaming

Tapestreamingduringwriteoperationshasamajorimpactontapebackupperformance.Almostalltapedrivescurrentlyonthemarketarefixedspeed,streamingtapedrives.Becausesuchdrivescanonlywritedataatonespeed,whentheyrunoutofdatatowritetotape,thetapemustslowdownandstop.Typically,whenthedrive'sbufferempties,thetapeismovingsoquicklythatitactuallyovershootstocontinuewriting,thedrivemustrewindthetapetolocatethepointwhereitstoppedwriting.

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()PhysicalTapeBlockSize

Thephysicaltapeblocksizecanaffectbackupperformance.Theblocksizeistheamountofdatawrittenbymediamanagementsoftwaretoatapeinonewriteoperation.Ingeneral,thelargerthetapeblocksize,thefasterthebackup.NotethatphysicaltapeblocksizeisnotcontrolledbyRMANortheOracledatabaseserver,butbymediamanagementsoftware.Seeyourmediamanagementsoftware'sdocumentationfordetails.

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()WritePhaseforDiskTheprincipalfactoraffectingthewritephasefordiskisthebuffersize.Whentheoutputofthebackupresidesondisk,eachchannelallocates4outputbuffersof1MBeach.Thediskchannelwritestheblockstothedisksubsystem.Notethatthereadphasewhenrestoringfilesisjustlikethewritephasewhenbackingupfiles,excepttheblocksmoveintheoppositedirection.

IfRMANreadsfromadiskasynchronously,thenitwritestothediskasynchronously.Whenwritingtodisk,youcanmakeuseofdiskI/Oslavesjustaswhenreading.

IfRMANisbackingupfilestoadiskbasedoutputdestinationstripedovermultipledisks,thenyoucanallocatemultiplechannels.Thenumberofchannelsislimitedonlytothenumberofdisksoverwhichthedestinationisstriped.ASMisoneexampleadestinationstripedovermultipledisks.

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()UsingV$ViewstoDiagnoseRMANPerformanceProblemsTypically,youbeginthetuningprocessbyusingV$ viewstodeterminewhereRMANbackupandrestoreoperationsareencounteringproblems.

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()MonitoringRMANJobProgresswithV$SESSION_LONGOPS()()You()canmonitortheprogressofbackupsandrestorejobsbyqueryingtheviewV$SESSION_LONGOPS .RMANusestwotypesofrows()inV$SESSION_LONGOPS :detailandaggregaterows.

Detailrowsdescribethefilesbeingprocessedbyonejobstep,whileaggregaterowsdescribethefilesprocessedbyalljobstepsinanRMANcommand.Ajobstepisthecreationorrestoreofonebackupsetordatafilecopy.Detailrowsareupdatedwitheverybufferthatisreadorwrittenduringthebackupstep,sotheirgranularityofupdateissmall.Aggregaterowsareupdatedwheneachjobstepcompletes,sotheirgranularityofupdateislarge.

Table212describesthecolumnsinV$SESSION_LONGOPS thataremostrelevantforRMAN.Typically,youwillviewthedetailrowsratherthantheaggregaterowstodeterminetheprogressofeachbackupset.

()()Table212ColumnsofV$SESSION_LONGOPSRelevantforRMAN

Column DescriptionforDetailRows

SID TheserversessionIDcorrespondingtoanRMANchannel.

SERIAL# Theserversessionserialnumber.Thisvaluechangeseachtimeaserversessionisreused.

OPNAME Atextdescriptionoftherow.ExamplesofdetailsrowsincludeRMAN: datafile copy ,RMAN: full datafile backup ,andRMAN: full datafile restore .

Note:RMAN: aggregate input andRMAN: aggregate output aretheonlyaggregaterows.

CONTEXT Forbackupoutputrows,thisvalueis2 .Forallotherrowsexceptproxycopy(whichdoesnotupdatethiscolumn),thevalueis1 .

SOFAR Themeaningofthiscolumndependsonthetypeofoperationdescribedbythisrow:

Forimagecopies,thenumberofblocksthathavebeenread.

Forbackupinputrows,thenumberofblocksthathavebeenreadfromthefilesbeingbackedup.

Forbackupoutputrows,thenumberofblocksthathavebeenwrittentothebackuppiece.

Forrestores,thenumberofblocksthathavebeenprocessedtothefilesthatarebeingrestoredinthisonejobstep.

Forproxycopies,thenumberoffilesthathavebeencopied.

TOTALWORK Themeaningofthiscolumndependsonthetypeofoperationdescribedbythisrow:

Forimagecopies,thetotalnumberofblocksinthefile.

Forbackupinputrows,thetotalnumberofblockstobereadfromallfilesprocessedinthisjobstep.

Forbackupoutputrows,thevalueis0 becauseRMANdoesnotknowhowmanyblocksthatitwillwriteintoanybackuppiece.

Forrestores,thetotalnumberofblocksinallfilesrestoredinthisjobstep.

Forproxycopies,thetotalnumberoffilestobecopiedinthisjobstep.

Eachserversessionperformingabackuporrestorejobreportsitsprogresscomparedtothetotalworkrequiredforajobstep.Forexample,ifyourestorethedatabasewithtwochannels,andeachchannelhastwobackupsetstorestore(atotaloffoursets),theneachserversessionreportsitsprogressthroughasinglebackupset.Whenasetiscompletelyrestored,RMANbeginsreportingprogressonthenextsettorestore.

()TomonitorRMANjobprogress:

BeforestartingtheRMANjob,createascriptfile(called,forthisexample,longops )containingthefollowingSQLstatement:

SELECTSID,SERIAL#,CONTEXT,SOFAR,TOTALWORK,

ROUND(SOFAR/TOTALWORK*100,2)"%_COMPLETE"

FROMV$SESSION_LONGOPS

WHEREOPNAMELIKE'RMAN%'

ANDOPNAMENOTLIKE'%aggregate%'

ANDTOTALWORK!=0

ANDSOFARTOTALWORK

StartRMANandconnecttothetargetdatabaseandrecoverycatalog(ifused).

StartanRMANjob.Forexample,enter:

RMAN>RESTOREDATABASE

WhiletheRMANjobisrunning,startSQL*Plusandconnecttothetargetdatabase,andexecutethelongops scripttochecktheprogressoftheRMANjob.IfyourepeatthequerywhiletheRMANjobprogresses,thenyouseeoutputsuchasthefollowing:

SQL>@longops

SIDSERIAL#CONTEXTSOFARTOTALWORK%_COMPLETE

8191103773661728.34

SQL>@longops

SIDSERIAL#CONTEXTSOFARTOTALWORK%COMPLETE

8191215133661758.75

SQL>@longops

SIDSERIAL#CONTEXTSOFARTOTALWORK%COMPLETE

8191296413661780.95

SQL>@longops

SIDSERIAL#CONTEXTSOFARTOTALWORK%COMPLETE

8191358493661797.9

SQL>@longops

norowsselected

Ifyourunthelongops scriptatintervalsoftwominutesormoreandthe%_COMPLETE columndoesnotincrease,thenRMANisencounteringaproblem.Referto"MonitoringRMANInteractionwiththeMediaManager"(rcmtroub.htm#i1008347)toobtainmoreinformation.

Ifyoufrequentlymonitortheexecutionoflongrunningtasks,thenyoucouldcreateashellscriptorbatchfileunderyourhostoperatingsystemthatrunsSQL*Plustoexecutethisqueryrepeatedly.

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()IdentifyingBottleneckswithV$BACKUP_SYNC_IOandV$BACKUP_ASYNC_IO

Youcanuse()theV$BACKUP_SYNC_IO ()andV$BACKUP_ASYNC_IO viewstodeterminethesourceofbackuporrestorebottlenecksandtoseedetailedprogressofbackupjobs.

V$BACKUP_SYNC_IO containsrowswhentheI/Oissynchronoustotheprocess(orthreadonsomeplatforms)performingthebackup.V$BACKUP_ASYNC_IO containsrowswhentheI/Oisasynchronous.AsynchronousI/OisobtainedeitherwithI/Oprocessesorbecauseitissupportedbytheunderlyingoperatingsystem.

Theresultsofabackuporrestorejobremaininmemoryuntilthedatabaseinstanceshutsdown.Thus,youcanquerytheviewsafterthejobcompletes.

()TodeterminewhetherthetapeisstreamingwhentheI/Oissynchronous:

StartSQL*Plusandconnecttothetargetdatabase.

QuerytheEFFECTIVE_BYTES_PER_SECOND columnintheV$BACKUP_SYNC_IO orV$BACKUP_ASYNC_IO view.

IfEFFECTIVE_BYTES_PER_SECOND islessthantherawcapacityofthehardware,thenthetapeisnotstreaming.IfEFFECTIVE_BYTES_PER_SECOND isgreaterthantherawcapacityofthehardware,thetapemayormaynotbestreaming.CompressionmaycausetheEFFECTIVE_BYTES_PER_SECOND tobegreaterthanthespeedofrealI/O.

SeeAlso:OracleDatabaseReference(../../server.111/b28320/toc.htm)formoreinformationabouttheseviews

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()IdentifyingBottleneckswithSynchronousI/O

TableofContents(toc.htm)OracleDatabaseBackupandRecoveryUser'sGuide(toc.htm)

Preface(preface.htm#sthref2)What'sNewinBackupandRecovery?(wnbradv.htm#BRADV021)IntroductiontoBackupandRecovery(rcmintro.htm#BRADV8001)GettingStartedwithRMAN(rcmquick.htm#BRADV89346)RecoveryManagerArchitecture(rcmarchi.htm#BRADV001)StartingandInteractingwiththeRMANClient(rcmcnctg.htm#BRADV005)ConfiguringtheRMANEnvironment(rcmconfb.htm#BRADV8002)ConfiguringtheRMANEnvironment:AdvancedTopics(rcmconfa.htm#BRADV006)

RMANBackupConcepts(rcmcncpt.htm#BRADV002)BackingUptheDatabase(rcmbckba.htm#BRADV8003)

WithsynchronousI/O,itisdifficulttoidentifyspecificbottlenecksbecauseallsynchronousI/Oisabottlenecktotheprocess.TheonlywaytotunesynchronousI/Oistocomparetherate(inbytes/second)withthedevice'smaximumthroughputrate.Iftherateislowerthantheratethatthedevicespecifies,thenconsidertuningthisaspectofthebackupandrestoreprocess.

()TodeterminetherateofsynchronousI/O:

StartSQL*Plusandconnecttothetargetdatabase.

QuerytheDISCRETE_BYTES_PER_SECOND columnintheV$BACKUP_SYNC_IO viewtodisplaytheI/Orate.

IfyouseedatainV$BACKUP_SYNC_IO ,thentheproblemisthatyouhavenotenabledasynchronousI/OoryouarenotusingdiskI/Oslaves.

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()IdentifyingBottleneckswithAsynchronousI/O()()LongwaitsarethenumberoftimesthebackuporrestoreprocesstoldtheoperatingsystemtowaituntilanI/Owascomplete.()()ShortwaitsarethenumberoftimesthebackuporrestoreprocessmadeanoperatingsystemcalltopollforI/Ocompletioninanonblockingmode.ReadyindicatesthenumberoftimeswhenI/Owasalreadyreadyforuse,sotherewasnoneedtomakeanoperatingsystemcalltopollforI/Ocompletion.

()TodeterminetherateofasynchronousI/O:

StartSQL*Plusandconnecttothetargetdatabase.

QuerytheLONG_WAITS andIO_COUNT columnsintheV$BACKUP_SYNC_IO viewtodisplaytheI/Orate.

ThesimplestwaytoidentifythebottleneckistofindthedatafilethathasthelargestratioforLONG_WAITS dividedbyIO_COUNT .Forexample,youcanusethefollowingquery:

BackingUptheDatabase(rcmbckba.htm#BRADV8003)BackingUptheDatabase:AdvancedTopics(rcmbckad.htm#BRADV007)ReportingonRMANOperations(rcmreprt.htm#BRADV8004)MaintainingRMANBackupsandRepositoryRecords(rcmmaint.htm#BRADV8007)

ManagingaRecoveryCatalog(rcmcatdb.htm#BRADV8015)RMANDataRepairConcepts(rcmrvcon.htm#BRADV89703)DiagnosingandRepairingFailureswithDataRecoveryAdvisor(rcmrepai.htm#BRADV246)

ValidatingDatabaseFilesandBackups(rcmvalid.htm#BRADV90063)PerformingFlashbackandDatabasePointinTimeRecovery(rcmflash.htm#BRADV80055)

PerformingCompleteDatabaseRecovery(rcmcomre.htm#BRADV8005)PerformingBlockMediaRecovery(rcmblock.htm#BRADV89781)PerformingRMANRecovery:AdvancedScenarios(rcmadvre.htm#BRADV008)PerformingRMANTablespacePointinTimeRecovery(TSPITR)(rcmtspit.htm#BRADV009)

TuningRMANPerformance(rcmtunin.htm#BRADV011)TroubleshootingRMANOperations(rcmtroub.htm#BRADV012)DuplicatingaDatabase(rcmdupdb.htm#BRADV010)CreatingTransportableTablespaceSets(rcmttbsb.htm#BRADV05141)TransportingDataAcrossPlatforms(rcmxplat.htm#BRADV89976)PerformingASMDataMigration(rcmasmmi.htm#BRADV12000)MakingUserManagedDatabaseBackups(osbackup.htm#BRADV016)PerformingUserManagedDatabaseFlashbackandRecovery(osrecvry.htm#BRADV017)

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SELECTLONG_WAITS/IO_COUNT,FILENAME

FROMV$BACKUP_ASYNC_IO

WHERELONG_WAITS/IO_COUNT>0

ORDERBYLONG_WAITS/IO_COUNTDESC

Note:IfyouhavesynchronousI/Obutyouhaveset BACKUP_DISK_IO_SLAVES ,thentheI/Owillbedisplayedin V$BACKUP_ASYNC_IO .

SeeAlso:OracleDatabaseReference(../../server.111/b28320/dynviews_part.htm#REFRN003)fordescriptionsoftheV$BACKUP_SYNC_IO and V$BACKUP_ASYNC_IO views

()

()TuningRMANBackupPerformance()Manyfactorscanaffectbackupperformance.Often,findingthesolutiontoaslowbackupisaprocessoftrialanderror.Toobtainthebestperformanceforabackup,followthestepsinthissectioninsequentialorder.

Thissectioncontainsthefollowingsteps:

Step1:RemovetheRATEParameterfromChannelSettings

Step2:IfYouUseSynchronousDiskI/O,SetDBWR_IO_SLAVES

Step3:IfYouFailtoAllocateSharedMemory,SetLARGE_POOL_SIZE

Step4:TunetheRead,Write,andCopyPhases

()

()Step1:RemovetheRATEParameterfromChannelSettingsAsexplainedin"RATEChannelParameter",theRATE parameteronachannelisintendedtoreduce,ratherthanincrease,backupthroughputsothatmorediskbandwidthisavailableforotherdatabaseoperations.Ifthebackupisnotstreamingtotape,thenmakesurethattheRATE parameterisnotset.

()ToremovetheRATEparameter:

Examineyourbackupscript.

Dooneofthefollowing:

IfthebackupisinaRUN command,thenremovetheRATE parameter,ifitisspecified,fromtheALLOCATE command.Skiptheremainingsteps.

2. IfthebackupisnotinaRUN command,thenstartRMAN,connecttothetargetdatabase,andproceedtothenextstep.

ExecutetheSHOWALL commandtoshowthecurrentlyconfiguredsettings.

RemovetheRATE parameter,ifitisset,fromtheCONFIGURECHANNEL command.

()

()Step2:IfYouUseSynchronousDiskI/O,SetDBWR_IO_SLAVESAsexplainedin"SynchronousandAsynchronousDiskI/O",someoperatingsystemssupportnativeasynchronousI/O.IfandonlyifyourdiskdoesnotsupportasynchronousI/O,thensetDBWR_IO_SLAVES .AnynonzerovalueforDBWR_IO_SLAVES causesafixednumberofdiskI/Oslavestobeusedforbackupandrestore,whichsimulatesasynchronousI/O.

()ToenablediskI/Oslaves:

StartSQL*Plusandconnecttothetargetdatabase.

Shutdownthedatabase.

SetDBWR_IO_SLAVES initializationparametertoanonzerovalue.

BysettingDBWR_IO_SLAVES ,thedatabasewriterprocesseswilluseslaves.Thus,youmayneedtoincreasethevalueofthePROCESSES initializationparameter.

Restartthedatabase.

RestarttheRMANbackup.

()

()Step3:IfYouFailtoAllocateSharedMemory,SetLARGE_POOL_SIZESettheLARGE_POOL_SIZE initializationparameterifthedatabasereportsanerrorinthealertlogstatingthatitdoesnothaveenoughmemoryandthatitwillnotstartI/Oslaves.Themessageshouldresemblethefollowing:

ksfqxcre:failuretoallocatesharedmemorymeanssyncI/Owillbeusedwhenever

asyncI/Otofilenotsupportednatively

ThelargepoolisusedforRMANandforotherpurposes,soitstotalsizeshouldaccommodatealluses.ThisisespeciallytrueifDBWR_IO_SLAVES hasbeensetandtheDBWRprocessneedsbuffers.

()Tosetthelargepoolsize:

StartSQL*Plusandconnecttothetargetdatabase.

Optionally,()queryV$SGASTAT.POOL todeterminewhichpool(sharedpoolorlargepool)thememoryforanobjectresides.

Setthe ()()LARGE_POOL_SIZE initializationparameterinthetargetdatabase.

YoucanexecuteanALTERSYSTEMSET statementtosettheparameterdynamically.TheformulaforsettingLARGE_POOL_SIZE isasfollows:

LARGE_POOL_SIZE=number_of_allocated_channels*

(16MB+(4*size_of_tape_buffer))

RestarttheRMANbackup.

SeeAlso:OracleDatabaseConcepts(../../server.111/b28318/toc.htm)formoreinformationaboutthelargepool,andOracleDatabaseReference(../../server.111/b28320/toc.htm)forcompleteinformationaboutinitializationparameters

()

()Step4:TunetheRead,Write,andCopyPhases

Thereareseveraltasksyoucanperformtoidentifyandremedybottlenecksthataffectbackupperformance.

()

()UsingBackupValidationToDistinguishBetweenReadandWriteBottlenecksOnereliablewaytodeterminewhethertheoutputdeviceorinputdiskI/OisthebottleneckinagivenbackupjobistocomparethetimerequiredtorunbackuptaskswiththetimerequiredtorunBACKUPVALIDATE ofthesametasks.BACKUPVALIDATE ofabackupperformsthesamediskreadsasarealbackupbutperformsnoI/Otoanoutputdevice.

()Tocomparebackupandvalidationtimes:

MakesureyourNLSenvironmentdateformatvariableissettoshowthetime.Forexample,settheNLSvariablesasfollows:

setenvNLS_LANGAMERICAN_AMERICA.WE8DEC

setenvNLS_DATE_FORMAT"MM/DD/YYYYHH24:MI:SS"

EdityourbackupscripttousetheBACKUPVALIDATE commandinsteadoftheBACKUP command.

Runthebackupscript.

ExaminetheRMANoutputandcalculatethedifferencebetweenthetimesdisplayedintheStartingbackupat andFinishedbackupat messages.

EditthebackupscripttousetheBACKUP commandinsteadoftheBACKUPVALIDATE command.

Runthebackupscript.

ExaminetheRMANoutputandcalculatethedifferencebetweenthetimesdisplayedintheStartingbackupat andFinishedbackupat messages.

Comparethebackuptimesforthevalidationandrealbackup.

IfthetimefortheBACKUPVALIDATE totapeisaboutthesameasthetimeforarealbackuptotape,thenreadingfromdiskisthelikelybottleneck.See"TuningtheReadPhase".

IfthetimefortheBACKUPVALIDATE totapeissignificantlylessthanthetimeforarealbackuptotape,thenwritingtotheoutputdeviceisthelikelybottleneck.See"TuningtheCopyandWritePhases".

()

()TuningtheReadPhaseRMANmaynotbeabletosenddatablockstotheoutputdevicefastenoughtokeepitoccupied.Forexample,duringanincrementalbackup(glossary.htm#i432786),RMANonlybacksupblockschangedsinceapreviousdatafilebackupaspartofthesamestrategy.Ifyoudonotturnonblockchangetracking(glossary.htm#CHDIFJHF),thenRMANmustscanwholedatafilesforchangedblocks,andfilloutputbuffersasitfindssuchblocks.Iffewblockschanged,andifRMANismakinganSBTbackup,thenRMANmaynotfilloutputbuffersfastenoughtokeepthetapedrivestreaming.

Youcanimprovebackupperformancebyadjustingthelevelofmultiplexing(glossary.htm#CHDFBDDG),whichisnumberofinputfilessimultaneouslyreadandthenwrittenintothesameRMANbackuppiece.ThelevelofmultiplexingistheminimumoftheMAXOPENFILES settingonthechannelandthenumberofinputfilesplacedineachbackupset.Thefollowingtablemakesrecommendationsforadjustingthelevelofmultiplexing.

()()Table213AdjustingtheLevelofMultiplexing

ASM StripedDisk Recommendation

No Yes Increasethelevelofmultiplexing.Determinewhichistheminimum,MAXOPENFILES orthenumberoffilesineachbackupset,andthenincreasethisvalue.

Inthisway,youincreasetherateatwhichRMANfillstapebuffers,whichmakesitmorelikelythatbuffersaresenttothemediamanagerfastenoughtomaintainstreaming.

No No IncreasetheMAXOPENFILESsettingonthechannel.

Yes n/a SettheMAXOPENFILESparameteronthechannelto1or2.

SeeAlso:

"MultiplexedBackupSets"(rcmcncpt.htm#i1015964)tolearnhowtheMAXOPENFILES andFILESPERSET settingsaffectthelevelofmultiplexing

"IncrementalBackups"(rcmcncpt.htm#i1007616)foraconceptualoverview

()

()TuningtheCopyandWritePhasesIfthereadphaseisperformingwell,thenthecopyorwritephasesareprobablythebottleneck.Inparticular,ifRMANissendingdatablockstothetapedrivefastenoughtosupportstreaming,butthetapeisnotstreaming,thentheSBTwritephaseisthebottleneck.Trytoimproveperformanceasfollows:

Ifthebackupisafullbackup(glossary.htm#i432658),thenconsiderusingincrementalbackups.

Incrementallevel1backupswriteonlythechangedblocksfromdatafilestotape,sothatanybottleneckonwritingtotapehaslessimpactonyouroverallbackupstrategy.Inparticular,iftapedrivesarenotlocallyattachedtothenodeofthedatabasebeingbackedup,thenincrementalbackupscanbefaster.See"MakingandUpdatingIncrementalBackups"(rcmbckba.htm#i1034163).

IfthebackupusestheBZIP2 compressionalgorithm,whichisthedefault,thenchangethecompressionalgorithmfromBZIP2 toZLIB .

ZLIB islessCPUintensivethanBZIP2 .See"ConfiguringtheBackupCompressionAlgorithm"(rcmconfa.htm#CHDEHCEB).

IfthedatabasehostusesmultipleCPUs,andifthebackupusesbinarycompression,thenincreasethenumberofchannels.

Ifthebackupisencrypted,thenchangetheencryptionalgorithmtoAES128 .

TheAES128 algorithmistheleastCPUintensive.See"ConfiguringtheBackupEncryptionAlgorithm"(rcmconfa.htm#CHDFAHHJ).

IfRMANisbackinguptotape,thentrythefollowingadjustments:

AdjustthesizeofthetapeI/Obuffers.

UsethePARMS andBLKSIZE parametersoftheALLOCATECHANNEL orCONFIGURECHANNELcommandtosetthesize.ThesizeofthetapeI/Obuffersisplatformdependent.TheBLKSIZE settingoverridesthedefault.

Adjustsettingsinthemediamanagementsoftware.

Anumberofmediamanagersettings,includingthetapeblocksize,mayaffectbackupperformance.

IfRMANisbackingupfilestoASM,thenincreasethenumberofchannels.

Forexample,ifRMANisbackingupthedatabasetoasinglediskgroupwith16physicaldisks,thenallocateorconfigureatleast4diskchannels,uptoamaximumof16.

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