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外文翻译--基于Java的访问远程数据库的高效的标准软件体系结构 英文版.pdf

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外文翻译--基于Java的访问远程数据库的高效的标准软件体系结构 英文版.pdf

FutureGenerationComputerSystems151999417–424EfficiencyofstandardsoftwarearchitecturesforJavabasedaccesstoremotedatabasesN.Zingirian,M.Maresca,S.NalinDipartimentodiElettronicaedInformatica,UniversityofPadua,Padua,ItalyAccepted14December1998AbstractNovelclient–serverarchitecturesforremotedatabaseaccessareincreasinglytakingadvantageofWebtechnology,adoptingWebbrowsersasgraphicuserinterfacesintheclientsandtraditionalSQLdatabasemanagementsystemsDBMSsintheservers.TheinteroperationbetweenstandardbrowsersandspecificDBMSsistodaysupportedbyanumberofsoftwarearchitecturesbasedontheJavavirtualmachineembeddedinlastgenerationbrowsers.Unfortunatelysuchsoftwarearchitectures,whichappearexcellentfromthepointsofviewofopennessandflexibility,introduceconspicuouslatenciesindatabaseaccess.Theobjectiveofthispaperistoidentifysuchlatenciesthroughtheanalysisofanumberofexperimentalresults.ThepaperdescribesfourdifferentsoftwarearchitecturessupportingJavabasedSQLdatabaseaccess,reportstheirperformancemeasurementsondifferenthardwareplatformsandcomparestheresultsobtained.c©1999ElsevierScienceB.V.Allrightsreserved.KeywordsCORBAJavaJDBCPerformanceevaluationVisualdatabaseaccess1.IntroductionThetraditionalapproachtoclient–serverdatabaseaccessisbasedonthecombinedactionofauserinterfacewritteninavisuallanguagei.e.theclientandastandardSQLenginei.e.theserver.Currently,thisapproachischallengedbynovelsolutionsbasedontheemergingWebparadigm1.IntheWebbasedsolutionstheuserinterface,typicallywritteninJava,isdownloadedbyabrowserfromtheserverandrunsonthebrowservirtualmachine.Themainpointofsuchsolutionsisthattheclientsoftwareresidesintheserversystemasauniquecopy,ratherthanbeingreplicatedintheclientsystems.Thisfactallowsthecostsofinstallation,configurationandmaintenanceoftheclientsoftwaretobereducedthankstothepossibilityofcentralisingalltheseoperationsattheserversite2.WebbasedaccesstoSQLdatabasescanbesupportedbyanumberofsoftwarearchitectures3characterizedbyadifferentcompositionofasetofbasiccomponents4.Unfortunatelysuchsoftwarearchitectures,whichappearexcellentfromthepointofviewofopennessandflexibility,introduceconspicuouslatenciesindatabaseaccess.Correspondingauthor.0167739X/99/–seefrontmatterc©1999ElsevierScienceB.V.Allrightsreserved.PIIS0167739X98000855418N.Zingirianetal./FutureGenerationComputerSystems151999417–424Fig.1.Softwarearchitecture1databaseaccessthroughJavasockets.TheobjectiveofthestudypresentedinthispaperistodescribefourdifferentsoftwarearchitecturesimplementingWebbasedSQLdatabaseaccessandtoreportandcomparetheirperformances,characterizingthesourcesofthelatenciesintroducedbyeacharchitecture.Thepaperisorganizedasfollows.FirstwedescribethestandardsoftwarearchitecturesforJavabaseddatabaseaccessSection2.ThenwepresentthetestbedusedandthemethodologyfollowedinourexperimentsSection3.FinallywepresenttheresultsoftheexperimentsSection4anddiscusstheperformanceprofileofthesoftwarearchitecturestestedSection5.AbriefsummarySection6concludesthepaper.2.SoftwarearchitecturesforJavabaseddatabaseaccessInthissectionwepresentthefoursoftwarearchitecturesforJavabaseddatabaseaccessthatweselectedforourinvestigation.Eacharchitecturecomplieswiththeclient–serverparadigmandconsistsofthreemainentitiestheclient,theserverandtheinteroperabilitycomponents.Theclientandtheserverarethesameineacharchitecturetheinteroperabilitycomponentsarethedistinctivefeatureforeacharchitecture.TheclientisaJavaenabledbrowser,theserverisaSQLdatabasemanagementsystemDBMSwhichacceptsremotenetworkconnectionsandqueries.WeassumethatthenetworkprotocolstackisbasedontheTCP/IPprotocolsuite.Theinteroperabilitycomponentsofeachsoftwarearchitecturearedescribedintherestofthesection.2.1.ArchitecturebasedonJavasocketconnectivitymodulesTheschemeofthearchitecturebasedonJavasocketconnectivitymodulesisdepictedinFig.1Theshadedblocksrepresentthesoftwaremodulesthattheprogrammerhastodeveloptointerconnecttheexistingcomponents.Theclientbrowserdownloadsanappletfromtheservermachineandrunsit.TheappletsendsthequeriesandreceivestheresponsesthroughtheJavasocketmodules.TheserverDBMSexchangesdatawiththeclientthroughasoftwarecomponentthatactsasanintermediatecustomagent.SuchanintermediatecustomagentreceivestheclientqueriesandsubmitsthemtothedatabasethroughthedatabaseAPIlibrary.TheconnectivitybetweentheappletandthecustomagentisbasedonTCP/IP.OntheclientsidecommunicationissupportedbythestandardJavasocketAPIontheserversidecommunicationissupportedbythestandardUNIXsocketinterface.Interoperationbetweentheappletandthecustomagentisbasedonacustomprotocolwhichsupportsthefundamentaldatabaseaccessoperationsopendatabase,submitquery,retrieveresponse,closedatabase.2.2.ArchitecturebasedonproprietaryDBMSJDBCdriverTheArchitecturebasedonproprietaryDBMSJDBCdriverisdepictedinFig.2.JavadataBaseconnectivityJDBCisastandardinterfacewhichallowsJavaappletsandapplicationstointeroperatewithdatabase.LikeinN.Zingirianetal./FutureGenerationComputerSystems151999417–424419Fig.2.SoftwarearchitecturefordatabaseaccessbasedonDBMSproprietaryJavaJDBC.Fig.3.SoftwarearchitecturefordatabaseaccessbasedonJavaJDBCandrequestbroker.thepreviousarchitecture,theclientbrowserdownloadsanappletfromtheservermachineandrunsit.TheappletaccessestheDBMSthroughthestandardprimitivesoftheJBDBCapplicationprogramminginterfaceJDBCAPI.TheJDBCAPIisavailableasapartofthestandardclassesoftheJavadeveloperkitsandoftheJavaenabledbrowserscompliantwitthelatestversionsofJava.TheJDBCclassesarenotspecificforanyparticularDBMS,exceptforoneclass,denotedtheJDBCdriver,whichimplementsthecommunicationprotocolrequiredbythespecificDBMSwhichitrefersto.ThespecificJDBCdriversareprovidedbytheDBMSvendorsorbythirdpartiesandaredynamicallylinkedtothestandardJDBCobjects.UsuallytheJDBCdriverisdownloadedfromtheserveralongwiththeclientapplet.TheDBMSdriverinteroperateswiththeDBMSoverthenetworkbytranslatingtheJDBCmethodsinproprietarymessagestoproprietaryservicerequestmessages.TheserverDBMSreceivesthequeries,sendstheresponsesandperformsalltheoperationsthroughitsproprietaryprotocol,withnoneedofadditionalinteroperabilitymodulesintheservermachine.2.3.ArchitecturebasedonJDBCrequestbrokermiddlewareThearchitecturebasedonarequestbrokerisdepictedinFig.3.Asinthepreviousarchitecture,theappletcommunicateswiththedatabasethroughthestandardJDBCAPIandthroughaspecificJDBCdriver.Asopposedtothepreviousarchitecture,theJDBCdriverdoesnotaccessthedatabasedirectlybutitaccessanintermediateobject,calledthebroker,runningontheservermachine,throughaproprietaryprotocol.Whentheappletrequestsaconnection,therequestbrokerdynamicallyinstantiatestwocomponentsaJDBCagent,andadatabaseagentspecificfortheDBMSadopted.TheserverDBMSandtheclientinteroperatethroughthedatabaseagentandthroughtheJDBCagentwhichinteractbymeansofaproprietaryprotocol.Theopennessandflexibilityadvantagesofusingtherequestbrokerandtheagentsarediscussedin5.420N.Zingirianetal./FutureGenerationComputerSystems151999417–424Fig.4.SoftwarearchitecturefordatabaseaccessbasedonCORBA.Table1SoftwareproductsusedascomponentsofthetestedsoftwarearchitecturesSoftwarecomponentSoftwareproductVendorDBMS1PostgreSQL6.1.1UniversityofCalifornia7BrowserNavigator4NetscapeJavasocketclassjava.net.socketNetscapeDBMSJDBCdriverclasspostgresql.driverUniversityofCaliforniaRequestbrokeroplrqbOpenlinkDatabaseagentpgr95svOpenlinkJDBCagentjdbcsvOpenlinkBrokerJDBCDriverclassopenlink.driverOpenlinkClientORBpackageorg.omg.CORBAVisigenic/NetscapeServerORBomniORB2OlivettiOracleResearchLabs2.4.ArchitecturebasedonCORBAinteroperabilitycomponentsTheCORBAbasedarchitectureisshowninFig.4.EveninthiscasetheappletcommunicateswiththeDBMSthroughanobjectorientedAPI.ThisAPIinstantiatesandinteroperateswithadatabaseaccessobjectwhichresidesintheservermachine.InteroperabilityissupportedbyapairoflibrariescalledobjectrequestbrokersORBs6whichcommunicatethroughtheInternetInterORBprotocolIIOP.OneORBisaJavapackagelocatedintheclientmachinewhiletheotherORBisalibrarylocatedintheservermachine.TheserverDBMScommunicateswiththedatabaseaccessobjectthroughtheDBMSapplicationprogramminginterface.ThedatabaseaccessobjectisdevelopedbythesystemintegratoranditsAPIisdescribedthroughaformalspecificationlanguagedenotedasinerfacedescriptionlanguageIDL.TheIDLsupportsreliableinteroperationbetweentheclientandtheserverinspiteofthefactthattheprogramsarewrittenindifferentlanguages.3.TestedandmethodologyInthissectionwedescribethetestbedthatweusedandthemethodologythatwefollowedtocarryouttheexperiments.WeinstalledtheDBMSonaservermachinePCPentiumPro,200MHz,32MbytesRAM,LinuxoperatingsystemandthedifferentsoftwarecomponentsinclientmachinesPCPentium166MHz,HP715100MHzandSunSparc575MHz,eachequippedwith32MBandrunningUnixoperatingsystems,choosingtheproductsreportedinTable1.Weidentifiedthreedatabaseoperationsasthebasicoperationstobetested,namelydatabaseopening,queryexecution,databaseclose.Thequeryexecutionweadoptedforourtestswasasingleselectionofanitemconsistingofa34bytelongstringfromatableofmorethan39000rowsoffourcolumnseach.Eachlatencymeasurementwasobtainedbyrepeatingeachexperimentmorethan6000timesandselectingtheminimumresult,inordertominimizetheincidentaloverheads.

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