资源描述：
《SQL Server查询优化器的测试：挑战性，技术性和经验性【外文翻译】》由会员上传分享，免费在线阅读，更多相关内容在行业资料-天天文库。
1、外文翻译原文TestingSQLServer’sQueryOptimizer:Challenges,TechniquesandExperiencesMaterialSource:IEEEDataEngineeringBulletinAuthor:LeoGiakoumakis,CesarGalindo-Legaria1IntroductionToday’squeryoptimizersprovidehighlysophisticatedfunctionalitythatisdesignedtoservealargevarietyofworkl
2、oads,datasizesandusagepatterns.Theyaretheresultofmanyyearsofresearchanddevelopment,whichhascomeatthecostofincreasedengineeringcomplexity,specificallyinvalidatingcorrectnessandmeasuringquality.Thereareseveraluniquecharacteristicsthatmakequeryoptimizersexceptionallycomplexsy
3、stemstovalidate,moresothanmostothersoftwaresystems.Queryoptimizershandleapracticallyinfiniteinputspaceofdeclarativedataqueries(e.g.SQL,XQuery),logical/physicalschemaanddata.Asimpleenumerationofallpossibleinputcombinationsisunfeasibleanditishardtopredictorextrapolateexpecte
4、dbehaviorbygroupingsimilarelementsoftheinputspaceintoequivalenceclasses.Thequeryoptimizationprocessitselfisofhighalgorithmiccomplexity,andreliesoninexactcostestimationmodels.Moreover,queryoptimizersoughttosatisfyworkloadsandusagescenarioswithavarietyofdifferentrequirements
5、andexpectations,e.g.tooptimizeforthroughoutorforresponsetime.Overtime,thenumberofexistingcustomersthatneedtobesupportedincreases,afactthatintroducesconstraintsinadvancingqueryoptimizationtechnologywithoutdisturbingexistingcustomerexpectations.Whilenewoptimizationsmayimprov
6、equeryperformancebyordersofmagnitudeforsomeworkloads,thesameoptimizationsmaycauseperformanceregressions(orunnecessaryoverhead)tootherworkloads.Forthosereasons,alargepartofthevalidationprocessofthequeryoptimizerismeanttoprovideanunderstandingofthedifferenttradeoffsanddesign
7、choicesinrespecttotheirimpactacrossdifferentcustomerscenarios.Atthesametime,thevalidationprocessneedstoprovideanassessmentofregressionriskforcodechangesthatmayhavealargeimpactacrossalargenumberofworkloadandquerytypes.2KeyChallengesThegoalofqueryoptimizationistoproduceeffic
8、ientexecutionstrategiesfordeclarativequeries.Thisinvolvestheselectionofanoptimalexecution
