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1、CS-TR-3994,UMIACS-TR-99-13XJoin:GettingFastAnswersFromSlowandBurstyNetworksTolgaUrhanMichaelJ.FranklinInstituteforAdvancedComputerStudiesInstituteforAdvancedComputerStudiesComputerScienceDepartmentComputerScienceDepartmentUniversityofMarylandUniversityofMarylandCollegePark,MD207
2、42CollegePark,MD20742urhan@cs.umd.edufranklin@cs.umd.eduAbstractThecombinationofincreasinglyubiquitousInternetconnectivityandadvancesinheterogeneousandsemi-structureddatabaseshasthepotentialtoenabledatabase-stylequeryingoverdatafromsourcesdistributedaroundtheworld.Traditionalque
3、ryprocessingtechniques,however,failtodeliveracceptableperformanceinsuchascenariofortwomainreasons:First,theyoptimizefordeliveryoftheentirequeryresult,whileon-lineuserswouldtypicallybene tfromreceivinginitialresultsasquicklyaspossible.Second,sloworburstydeliveryofdatafromremoteso
4、urcescanstallqueryexecution,makingthealreadyinadequatebatch-likebehaviorevenworse.Bothoftheseproblemscanbeaddressedusingfullypipelinedqueryexecution.Thesymmetrichashjoinoperatorsupportssuchpipelining,butitrequiresallbasedataandintermediateresultstobememory-resident,whichisunacce
5、ptableforcomplexqueriesoverlargedatasets.Inthispaperwepresentamulti-threadedextensionofthesymmetrichashjoin,calledXJoin,thatcanexecutee ectivelywithfarlessmemory.Byreactivelyschedulingbackgroundprocessing,XJoinhidesintermittentdelaysindataarrivaltoproducemoretuplesearlier.XJoini
6、ncludesaveryecient,on-the-
yalgorithmforpreventingduplicatesfrombeingcreatedbyitsindependentlyrunningthreads.WehaveimplementedtheXJoinoperatorandaddedittothePREDATORObject-RelationalDBMS.UsingthisimplementationalongwithtracesobtainedbymonitoringInternetdatadelivery,weshowthatXJ
7、oinisane ectivesolutionforprovidingfastqueryresponsestouserseveninthepresenceofslowandburstyremotesources.1Introduction1.1Wide-AreaQueryProcessingTheexplosivegrowthoftheInternetandtheWorldWideWebhasmadetremendousamountsofdataavailableon-line.Currently,searchingforinformationinth
8、ishugedatabaseisusuallydoneusingnavigationalmet
