Performance Improvement Methods.docx

Performance Improvement Methods.docx

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PerformanceImprovementMethods

PerformanceImprovementMethods

ThischapterdiscussesOracleimprovementmethods.

Thischaptercontainsthefollowingsections:

∙TheOraclePerformanceImprovementMethod

∙EmergencyPerformanceMethods

TheOraclePerformanceImprovementMethod

OracleperformancemethodologyhelpsyoutopinpointperformanceproblemsinyourOraclesystem.Thisinvolvesidentifyingbottlenecksandfixingthem.Itisrecommendedthatchangesbemadetoasystemonlyafteryouhaveconfirmedthatthereisabottleneck.

Performanceimprovement,byitsnature,isiterative.Forthisreason,removingthefirstbottleneckmightnotleadtoperformanceimprovementimmediately,becauseanotherbottleneckmightberevealed.Also,insomecases,ifserializationpointsmovetoamoreinefficientsharingmechanism,thenperformancecoulddegrade.Withexperience,andbyfollowingarigorousmethodofbottleneckelimination,applicationscanbedebuggedandmadescalable.

Performanceproblemsgenerallyresultfromeitheralackofthroughput,unacceptableuser/jobresponsetime,orboth.Theproblemmightbelocalizedbetweenapplicationmodules,oritmightbefortheentiresystem.

Beforelookingatanydatabaseoroperatingsystemstatistics,itiscrucialtogetfeedbackfromthemostimportantcomponentsofthesystem:

theusersofthesystemandthepeopleultimatelypayingfortheapplication.Typicaluserfeedbackincludesstatementslikethefollowing:

∙"Theonlineperformanceissobadthatitpreventsmystafffromdoingtheirjobs."

∙"Thebillingruntakestoolong."

∙"WhenIexperiencehighamountsofWebtraffic,theresponsetimebecomesunacceptable,andIamlosingcustomers."

∙"Iamcurrentlyperforming5000tradesaday,andthesystemismaxedout.Nextmonth,werollouttoallourusers,andthenumberoftradesisexpectedtoquadruple."

Fromcandidfeedback,itiseasytosetcriticalsuccessfactorsforanyperformancework.Determiningtheperformancetargetsandtheperformanceengineer'sexitcriteriamakemanagingtheperformanceprocessmuchsimplerandmoresuccessfulatalllevels.Thesecriticalsuccessfactorsarebetterdefinedintermsofrealbusinessgoalsratherthansystemstatistics.

Somerealbusinessgoalsforthesetypicaluserstatementsmightbe:

∙"Thebillingrunmustprocess1,000,000accountsinathree-hourwindow."

∙"AtapeakperiodonaWebsite,theresponsetimewillnotexceedfivesecondsforapagerefresh."

∙"Thesystemmustbeabletoprocess25,000tradesinaneight-hourwindow."

Theultimatemeasureofsuccessistheuser'sperceptionofsystemperformance.Theperformanceengineer'sroleistoeliminateanybottlenecksthatdegradeperformance.Thesebottleneckscouldbecausedbyinefficientuseoflimitedsharedresourcesorbyabuseofsharedresources,causingserialization.Becauseallsharedresourcesarelimited,thegoalofaperformanceengineeristomaximizethenumberofbusinessoperationswithefficientuseofsharedresources.Ataveryhighlevel,theentiredatabaseservercanbeseenasasharedresource.Conversely,atalowlevel,asingleCPUordiskcanbeseenassharedresources.

TheOracleperformanceimprovementmethodcanbeapplieduntilperformancegoalsaremetordeemedimpossible.Thisprocessishighlyiterative,anditisinevitablethatsomeinvestigationswillbemadethathavelittleimpactontheperformanceofthesystem.Ittakestimeandexperiencetodevelopthenecessaryskillstoaccuratelypinpointcriticalbottlenecksinatimelymanner.However,priorexperiencecansometimesworkagainsttheexperiencedengineerwhoneglectstousethedataandstatisticsavailabletohim.Itisthistypeofbehaviorthatencouragesdatabasetuningbymythandfolklore.Thisisaveryrisky,expensive,andunlikelytosucceedmethodofdatabasetuning.

TheAutomaticDatabaseDiagnosticMonitor（ADDM）implementspartsoftheperformanceimprovementmethodandanalyzesstatisticstoprovideautomaticdiagnosisofmajorperformanceissues.UsingADDMcansignificantlyshortenthetimerequiredtoimprovetheperformanceofasystem.SeeChapter 6,"AutomaticPerformanceDiagnostics"foradescriptionofADDM.

Today'ssystemsaresodifferentandcomplexthathardandfastrulesforperformanceanalysiscannotbemade.Inessence,theOracleperformanceimprovementmethoddefinesawayofworking,butnotadefinitivesetofrules.Withbottleneckdetection,theonlyruleisthattherearenorules!

Thebestperformanceengineersusethedataprovidedandthinklaterallytodetermineperformanceproblems.

StepsinTheOraclePerformanceImprovementMethod

1.Performthefollowinginitialstandardchecks:

a.Getcandidfeedbackfromusers.Determinetheperformanceproject'sscopeandsubsequentperformancegoals,aswellasperformancegoalsforthefuture.Thisprocessis