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ID:44869108
大小:43.50 KB
页数:6页
时间:2019-10-31
《数据仓库的7层优化》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、SevenLayersofOptimizationGoingfromDetailtoSummaryIfonelooksattheevolutionofthedatawarehousearena,thereisaclearpatternthatemerges.Thatpatternisoneofcompromisingtheprojectinordertoovercometechnicalbarriersattheexpenseofbusinessvalue.Onesuchcompromiseistheautomaticuseofsummarydataor
2、datamodelsgearedtowardsasingularapplication.Giventhediversenatureofthereaders,Iwillgivesomebriefbackgroundinordertolevelsetthediscussion.Inthebeginning,companieswouldsimplyextractdataofftheoperationalsystemsandputthedataintoanotherdatabaseforbusinessuserstoanalyze.Typicallythedat
3、abaseusedforanalysiswasthesameastheoneusedforOLTP(On-LineTransactionProcessing)processing.ThiswasdonetoseparatethelongerrunningandmorecomplexanalysisworkloadsfrominterferingwiththemoremissioncriticalOLTPwork.Itisalsoimportanttonotethatmostoperationalsystemshavedatastoredinanormal
4、izedmodel,thatisonewherethedataisstoredaccordingtocertainrulesthateliminateredundancyandsimplifydatarelationships.WhilegoodfortheOLTPworkload,suchamodelofteninhibitedmostdatabasesfromrunningtheanalyticalqueriesforreasonsdiscussedbelow.Asthedatavolumegrewontheanalyticalsystemsthet
5、imeforqueriestooklongerandlonger.Twofactorscameintoplayhere.SincetheanalyticalsystemsdidnotneedtosupporttheOLTPworkloadmanydevelopersstartedtopre-planfortheanswersets.Thispre-planningincludedcreatingsummarytables(datathatispre-aggregated),placingindexesonthesystem(thiseliminatedt
6、heneedtoscanlargevolumesofdata),denormalizingthemodel(puttingdataintoonetableasopposedtohavingtablesthatneedtobejoinedtogether),andstoringthedatainsortedorder(thusavoidingandsortactivity).Thesearethefourareasthatmostdatabasehaveproblemswithandallofthemrequirepriorknowledgeofthean
7、alysisandreportsbeingrequested.Thesecondfactorwasthatthepeopleinchargeofthedevelopmentofthesesystemsdidnothaveabackgroundinrealdatawarehouseenvironments.Theyweretrainedinoptimizingtheperformancebymanipulatingthedatabaseparametersanddatamodels.Intheearlydaysthiswasdeemedacceptable
8、asbeforetheuserscouldgetlittletonoinform
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