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DiagnosingSQL

PerformanceProblems

KarenMorton

Sr.TechnicalConsultant

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AnEmbarcaderoOracleCommunityWebinar

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karenmorton.blogspot.com

karen_morton

karen.morton@enkitec.com

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July31

DiagnosingSQLPerformanceProblems

August29

MakingSQLPerformanceSoluGonsSGck

September26

MakingImpaculPerformanceChanges

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4

Whensomethingsonfire,

whatdoyoudo?

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Put.

It.

Out.

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Timeisaluxury.

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PlanofAack

EvaluatethesituaGonatherdata&determineproblemscope

Propose&eliminate(postpone)opGonsArethereanyquickfixes?

ImplementbestopGonBest=quickestalternaGvetoachievecorrecGon

ValidatesoluGon7

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Whatalertedtheissue?

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Usercomplaintsmayormaynot

beobviousinmonitoringtools.

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Howdoyoumonitor

andanalyzedatabase

acGvity?

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Doyouhavelicensesfor

ASH&AWRuse?

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Ifnot,doyouuseS-ASHor

Statspackor3rdpartyproduct?

S-ASHissimulatedASH

(homegrownorseewww.ashmasters.com).

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Remember:DiagnosGc&TuningPacks

neededtolegallyuseASH/AWR.

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WhatisincludedwithvariousOracleManagementPacks?

hp://docs.oracle.com/cd/E11882_01/license.112/e10594/opGons.htm#CIHIHDDJ

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TopSQL(byelapsedGme)

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TopSQL(ASH)

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EvaluatetheSituaGon

DetermineifstressinsideoroutsidethedatabaseOSresources?Networkresources?Storageresources?

etanaccuratedescripGonoftheproblemWhatistheproblemscope?WhatistheexpectedvscurrentresponseGme(s)?Doestheproblemoccurrandomlyorrepeatedly?Whathaschanged?

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DBAs

Developers

SANAdmins

NetAdmins

OSAdmins

Managers

Users

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Nothing

has changed!

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But

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If

nothingchanged,whyissomethingdifferent?

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Ch-ch-ch-ch-changes

StaGsGcsDatavolumeDatadistribuGon

Cardinalityfeedback ParametersOutsidethedatabase

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homagetoDavidBowie

SQLisnotlikely

theproblemifthe

changeisoutside

thedatabase.

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SQLProblem?

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SameexecuGonplanonbothnodes.

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OutsidetheDatabase?

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StaGsGcs?

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update t_cust_acct_offr_pndg_trckg!set prcss_flg = Y!

where bat_job_exec_trckg_id = :B1!and cust_acct_offr_trckg_id = :B2 ;!

Uniqueindexavailableon

thesecolumns

Processwouldexecutethisupdateover1.5millionGmes.

TotalesGmatedGmetocomplete~500hours.

LogicalIOpersecondover111K

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Aerstatscollected,

jobcompletedin40minutes.

ResponseGmeforsingleexecuGondroppedfrom1.3to.002seconds.

LogicalIOperseconddroppedfromover111Kto933.

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Statscollectedat1%usingFORALLCOLUMNSSIZE254

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Statsre-collectedwithauto_sample_sizeusingFORALLCOLUMNSSIZEAUTO

Aerstatsre-collected,

responseGmedroppedfrom43minutesto.01second.

LIOdroppedfrom4.6millionto4

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OtherstaGsGcsissues

CollecttoofrequentlyEvenminorchangecanresultinbigplanchanges

Collecttoomanyhistograms(ornotenough)ColumnswithhundredsofdisGnctvalues

DynamicsamplingdisabledDefaultsused

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QuickStaGsGcsFixes

Collectonneededobjects!dbms_stats.gather_table_stats!

Reverttopreviousstatsdbms_stats.restore_table_stats!

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CardinalityFeedback

ComparescardinalityesGmatestoactualrowcounts

Ifenoughdifferencefound,opGmizerappliesfudgefactortocorrecttheesGmate

OPT_ESTIMATEhint SomeGmesesGmatesimprovebutresponseGmedecreases

Controlledby_optimizer_use_feedback!28

Seehp://kerryosborne.oracle-guy.com/2011/07/cardinality-feedback/

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Example

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CardinalityFeedback!

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UnstablePlans(AWR)

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QuickCFFixes

TurnoffCF(sessionorinstancelevel)!_optimizer_use_feedback = FALSE!

UseSQLProfiletoreplacebadplanwithgood!

UsehintonsingleSQLselect /*+

opt_param(_optimizer_use_feedback

false) */ !31

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Parameters

opGmizer_index_cost_adj opGmizer_index_caching db_file_mulGblock_read_count pga_aggregate_target cursor_sharing

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Watchoutforhiddenparametersthathavebeenchanged!

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QuickParameterFixes

JustsayNo!Onlychangeaparameteraercarefuland

comprehensivetesGng

Setbacktodefault UseSQLProfiletoreplacebadplanwithgood!

Useopt_paramhintforindividualSQLtooverrideeffectsifpossible

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HowSQLiswrien

isnottypicallytheproblem

whenperformancedegradeswithouta

planchange.

CheckAWRorStatspackhistorytodetermineifplanchanged.

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CheckAWRforExecuGonInfo

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3MostCommonRewriteReasons

QuerytransformaGonproblems DatatypeoddiGesorcomplexexpressions Proceduralvsset-basedapproach

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QueryTransformaGon

DevelopersusuallywriteSQLinstylesimplesttounderstand

Notnecessarilythemostefficient OraclerewritesSQLforbeerperformance TransformaGonscanbeseenintheexecuGonplan(reverseengineertheplantotheSQL)

TransformaGonbenefitscanbepreventedorreducedbycertaintechniques

DISTINCT,ROUPBY,outerjoins,etc38

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Datatypes&Expressions

Choosingthewrongdatatypeforacolumn

Usingcomplexexpressionsinpredicateswith/withoutproperindexing(FBI)39

SQL> select '20111231' - '20111201' from dual ; 30!!SQL> select '20120102' - '20111231' from dual ; 8871!!SQL> select to_date('20120102','yyyymmdd') !

to_date('20111231','yyyymmdd') from dual ; ! !2!

WHERE my_func1(my_func2(col)) = col . . .!!

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ProceduralSQL

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Listofemployeeswhospentthesamenumberofyearsineachjobtheyheld.

Accesssametabletwice

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Set-basedSQL

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Singletableaccess

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Stopthinking

row-by-row!

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Recap

Iftheproblemisoutsidethedatabase,SQLisrarelythemainproblem

StaGsGcs(planchanges)aretheprimeculpritifSQLperformancegoesfromgoodtobad

Findwhatchanged! Trytokeepinstanceparametersatdefaults

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Recap

WhenwriGngSQLThinkliketheopGmizer(trytoavoidquerytransformaGonpialls)

UseproperdatatypesWatchoutforcomplexexpressionsThinkinsets!

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Q&A

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Thankyou!