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时间:2020-06-11
《数据仓库的7层优化.doc》由会员上传分享,免费在线阅读,更多相关内容在应用文档-天天文库。
1、SevenLayersofOptimizationGoingfromDetailtoSummaryIfonelooksattheevolutionofthedatawarehousearena,thereisaclearpatternthatemerges.Thatpatternisoneofcompromisingtheprojectinordertoovercometechnicalbarriersattheexpenseofbusinessvalue.Onesuchcompromiseistheautomaticuseofsummarydataordatamodelsgear
2、edtowardsasingularapplication.Giventhediversenatureofthereaders,Iwillgivesomebriefbackgroundinordertolevelsetthediscussion.Inthebeginning,companieswouldsimplyextractdataofftheoperationalsystemsandputthedataintoanotherdatabaseforbusinessuserstoanalyze.Typicallythedatabaseusedforanalysiswasthesa
3、meastheoneusedforOLTP(On-LineTransactionProcessing)processing.ThiswasdonetoseparatethelongerrunningandmorecomplexanalysisworkloadsfrominterferingwiththemoremissioncriticalOLTPwork.Itisalsoimportanttonotethatmostoperationalsystemshavedatastoredinanormalizedmodel,thatisonewherethedataisstoredacc
4、ordingtocertainrulesthateliminateredundancyandsimplifydatarelationships.WhilegoodfortheOLTPworkload,suchamodelofteninhibitedmostdatabasesfromrunningtheanalyticalqueriesforreasonsdiscussedbelow.Asthedatavolumegrewontheanalyticalsystemsthetimeforqueriestooklongerandlonger.Twofactorscameintoplayh
5、ere.SincetheanalyticalsystemsdidnotneedtosupporttheOLTPworkloadmanydevelopersstartedtopre-planfortheanswersets.Thispre-planningincludedcreatingsummarytables(datathatispre-aggregated),placingindexesonthesystem(thiseliminatedtheneedtoscanlargevolumesofdata),denormalizingthemodel(puttingdataintoo
6、netableasopposedtohavingtablesthatneedtobejoinedtogether),andstoringthedatainsortedorder(thusavoidingandsortactivity).Thesearethefourareasthatmostdatabasehaveproblemswithandallofthemrequirepriorknowledgeoftheanalysisandreportsbeingrequested.Thesecondfactorwasthatthepeopleinchargeofthedevelopme
7、ntofthesesystemsdidnothaveabackgroundinrealdatawarehouseenvironments.Theyweretrainedinoptimizingtheperformancebymanipulatingthedatabaseparametersanddatamodels.Intheearlydaysthiswasdeemedacceptableasbeforetheuserscouldgetlittletonoinform
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