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1、AFullyPipelinedXQueryProcessorLeonidasFegarasRanjanDashYingHuiWangUniversityofTexasatArlington,Arlington,TX76019-19015fegaras@cse.uta.eduABSTRACTlatencyandthroughput.Wepresentahigh-performance,pull-basedstreamingpro-²Weaimataframeworkthatise®ectiveforcasualces
2、sorforXQuery,calledXQPull,thatcanhandlemanyad-hocqueriesthatproduceoutputfarsmallerthanessentialfeaturesofthelanguage,includinggeneralpredi-theinputstream.Ourgoalistobuildasystemthat,cates,recursivequeries,backwardaxissteps,andfunctionformostqueries,requiresam
3、emoryfootprintpropor-calls,usingaverysmallamountofcaching.Ourframeworktionaltothesizeofthequeryoutput,ratherthantheisbasedonanewtypeofeventstreams,calledretardedqueryinput.streams,whichallowmultipleandnestedstreamstobein-terleavedinthesamephysicalstream,whilep
4、ostponingthe²Manyine±ciencies,suchassomeformsofbackwardcachingofinputeventsuntilisabsolutelynecessary,typ-steps,canberemovedbywell-knownoptimizationsicallyattheendofthequeryevaluation,justbeforethetechniques.Thesemethodscanbeevenmoree®ec-resultsarereadytoprint
5、.tivebyexploitingtypeinformation.SinceXQueryisTuringcomplete,though,theseoptimizationsare1.INTRODUCTIONnotcompleteandcannotremoveallformsofine±-ciency.OurframeworkisfocusedonqueryprocessingWepresentahigh-performance,pull-basedstreamingpro-onschema-lessdataonly
6、,whichisdoneafterallnec-cessorforXQuery,calledXQPull,thatcanhandlemanyessaryoptimizationshavebeenapplied.essentialfeaturesofthelanguageusingasmallamountofcachingandhavingahighthroughputrateandafastla-Thecontributionsofourworkaresummarizedasfollows:tency.Whileo
7、therstreamingapproachescacheeventsea-gerlytopreservethesemanticsofqueryoperations,oursys-²Weintroduceanewtypeofeventstreams,calledre-tempostponescachinguntilisabsolutelynecessary,typi-tardedstreams,andanewframeworkforpull-basedcallyattheendofthequeryevaluation
8、,justbeforethestreamprocessingbasedonthesestreams.Aretardedresultsarereadytoprint.Thisisaccomplishedwithastreamallowsmultipleandnestedstreamstobein-noveldesignofeventstreamsthatinc
