24-Appendix-PEPATT.ppt

(Appendix)PerformanceEnhancingPatterns,Objectives,Aftercompletingthislesson,youshouldbeableto:UnderstandafewperformanceenhancingpatternsandAntiPatternsUnderstandafewgeneraldesignconsiderationsUnderstandafewnewtechnologiesthatcanhaveanimpactonperformanceWorkwithaHSQLdatabase,RoadMap,DesignPatternsAntiPatternsGeneralDesignTipsNewTechnologiesHSQLDatabase,DesignPatterns,ArearepeatableprocessordesignaddressingaspecificissueorprobleminthedevelopmentofasystemArepredictableintheirfunctionandareconsistentintheirprosandconsAreconceptsthatallowforacommonmethodtoquicklyandeffectivelycommunicatecomplexideologytoothersAllowfortheacceleratededucationoftheconceptforthosenewtoitAddresstheissueofreinventingthewheel,FastPath,ImprovestheresponsetimebyreducingtheamountofprocessingrequiredtoaccessmainfunctionalityIsanalogoustotheconceptofalocaltrainandanexpresstrainExamples:Providedefaultswhenauserdoesnotwanttogothroughthedetailsofeachstepinaconfigurationwizard.Avoidprotocolencodingforamessageonasocketconnectiontoaprocessonthesamecomputer.,FirstThingsFirst,Focusonprocessingtasksthatareimportant.Ifeverythingcannotbecompletedwithinthetimeavailable,thentheleastimportanttaskswillbetheonesomitted.Assignprioritiestotasksandexecutethemsothatthemostimportantactivitiesreceivepreference.Iftheoverloadisnottemporary,reducetheamountofprocessingrequired,orupgradetheprocessingenvironment.,AlternateRoutes,SpreadthedemandforhighusageobjectstodifferentobjectsorlocationsReducecontentiondelaysfortheobjectsAreacommonoccurrenceinDBsystemsUseahashingalgorithmfordate-timestampHavedifferentkeyassignmentsAccessdifferenttablesastheupdatesareexecutedReducedelaysduetoserializationReducevariabilityinperformance,FlexTime,PushesthedemandforhighusageobjectstoadifferentperiodoftimeReducescontentiondelaysforobjectsComplementsthealternateroutespatternReducesthetimethatprocesseswaitinqueuesMakesurethateveryrequestdoesnotchoosethesamealternatetime!MayactuallyrequiremoreprocessingProducingreportsaheadofscheduleandstoringuntilneeded,Batching,Combinesfrequentrequestsforservicestosavetheoverheadofinitialization,transmission,andterminationprocessingfortherequestCombinesrequestsintobatchessothattheoverheadprocessingisexecutedoncefortheentirebatchinsteadofforeachindividualitemIsperformedbythesenderorreceiveroftherequestReducesprocessingbygettingabatchofmessagestoprocessratherthanoneatatime,SlenderCyclicFunctions,AreusedwhenprocessingmustexecuteatregularintervalsArecommoninembeddedreal-timesystemsUsesensorreadingsGeneratereportsArchivedataIdentifythefunctionsthatexecuterepeatedlyatregular,specifictimeintervals,andminimizetheirprocessingrequirementsExample:archivingdatafromaRAMmemorybanktoaDBInstrumentsystemsandmonitortheirperformanceovertimefortheearlywarningofpotentialproblems,FastLaneReader,Providesamoreefficientwaytoaccessread-onlydatafromadatabaseMakesuseofaDataAccessObject(DAO)toaccessthedatabaseinsteadoftransactionalEJBsAvoidstheoverheadofEJBsandtheEJBcontainerDesignyourDAOsothatitcanbetailoredtoreturnonlywhatyouneed,andlimitthenumberofrowsreturned.Shouldnotbeusedwhenthedatabeingaccessedchangesrapidlyorwhenthetoleranceforslightlystaledataisverysmallbecausethereisariskofthedatabeingstale,SectionSummary,Inthissection,youlearnedabout:FastpathFirstthingsfirstAlternateroutesFlextimeBatchingSlendercyclicfunctionsFastlanereader,RoadMap,DesignPatternsAntiPatternsGeneralDesignTipsNewTechnologiesHSQLDatabase,AntiPatterns,DocumentcommonmistakesmadeduringsoftwaredevelopmentaswellastheirsolutionsTellhowtogofromaproblemtoabadsolutionwhatnottodoTellhowtogofromabadsolutiontoagoodsolutionthemeanstoturnaroundThepresenceoftheseAntiPatternspresentssignificantlimitstoscalabilityandperformance.,ExcessiveDynamicAllocation,Withdynamicallocation,objectsarecreatedwhentheyarefirstaccessedandthendestroyedwhentheyarenolongerneeded.Thiscanoftenbeagoodapproachtostructuringasystem,providingflexibilityinhighlydynamicsituations.Excessivedynamicallocation,however,addressesthefrequent,unnecessarycreationanddestructionofobjectsofthesame.Lazyloadingofobjectsandcachingcanhelpminimizeexcessivedynamicallocation.,CircuitousTreasureHunt,Dataretrievedfromafirsttableisusedtosearchasecondtable.Thisdataisfurtherusedtoretrievedatafromanothertableandsoonuntilthefinalresultsareobtained.Performanceimpactistheextraprocessingrequiredtoidentifythefinaloperationtobecalledandinvokingit.Indistributedobjectsystemsthiscanbeworse,whereobjectsmayresideinotherprocessesandonotherprocessors.Whentheinvocationcausestheintermediateobjectstobecreatedanddestroyed,theperformanceimpactisgreater.Eachcontextswitchmaycausetheworkingsetofthecalledobjecttobeloaded.,One-LaneBridge,ThesoftwareanalogytotheOneLaneBridgeisapointintheexecutionwhereoneoronlyafewprocessesmaycontinuetoexecuteconcurrently.Allotherprocessesmustwait.Indatabaseapplications,alockensuresthatonlyoneprocessmayupdatetheassociatedportionofthedatabaseatatime.Usingasynchronizedthreadblockwillcreatesuchasituation.,UnnecessaryProcessing,Thesoftwareapplicationspendstimeinprocessingseveralstepsthatcanbeeliminated.Excessiveloggingisagoodexampleofunnecessaryprocessing.,SisyphusListSubset,ThisisbasedontheGreekmythofSisyphuswhowasdamnedforalleternitytopushastoneupahillonlytowatchitrollbackdownagain.Theentirelistisfirstretrieved,fromwhichasubsetislaterextracted.Thisprocessisrepeatedoverandoveragain.,ThegodClass,Agodclassisonethatperformsmostoftheworkofthesystem,relegatingotherclassestominor,supportingroles.Thiscouldimpactperformance,asthisclassbecomesthecentralpointofprocessingbothbusinesslogicaswellasdata.Thegodclass,inmostcases,becomesverydifficulttomaintain.,SectionSummary,Inthissection,youlearnedabout:ExcessivedynamicallocationCircuitoustreasurehuntOnelanebridgeUnnecessaryprocessingSisyphuslistsubsetThegodclass,RoadMap,DesignPatternsAntiPatternsGeneralDesignTipsNewTechnologiesHSQLDatabase,Exceptions,Throwingexceptionsisexpensiveasitconsumesbothprocessingaswellasmemory.Dontthrowexceptionswhenyoudonthaveto.,Logging,MakesureyourapplicationisnotdoingtoomuchstandardI/Oorexcessivelogging.Eithersituationcouldsignificantlyslowsystemperformance.Inproductionenvironments,removeallSystem.out.println()statementsfromyourcode,asthesestatementsshouldbeusedonlyindevelopmentenvironmentsfordebugging.,SectionSummary,Inthissection,youlearnedafewgeneraldesigntips.,RoadMap,DesignPatternsAntiPatternsGeneralDesignTipsNewTechnologiesHSQLDatabase,NewTechnologies,Inthelastfewyearstherehavebeenawidearrayoftechnologiesthathavematured.Someofthesehelpimprovetheperformanceofsoftwaresystemsindifferentways.Wewillexamineafewoftheseinthenextfewslides.HibernateAJAXXMLstreaming,Hibernate,Isapowerful,highperformanceobject/relationalpersistenceandqueryserviceLetsyoudeveloppersistentclassesfollowingobject-orientedidiomsAssociationInheritancePolymorphismCompositionCollections,Hibernate,AllowsyoutoexpressqueriesinitsownportableSQLextension(HQL),aswellasinnativeSQL,orwithobject-orientedcriteriaImplementscertainoptimizationsmuchmoreefficientlythantypicalhandwrittenJDBCCachingOuterjoinassociationfetchingJDBCbatchingandsoonResultsinahugereductionincodeandanenormousincreaseinperformance,AJAX,StandsforAsynchronousJavaScriptAndXMLIsatechniqueusedtobuildrichinteractiveWebapplicationsIncreasestheWebpagesinteractivity,speed,andusabilitybyexchangingsmallamountsofdatawiththeserverbehindthescenesDoesnotrequirethattheentireWebpagebereloadedeachtimetheusermakesachange,AJAX,MakesusersfeelthatWebpagesaremoreresponsiveAfewexamplesinclude:GoogleMaps()AppleStore()KayakTravelSearch(),XMLProcessing,XMLprocessingcanbeanexpensiveoperation.DOMparsers,thoughveryeasytouse,arenotonlymemoryintensive,butcanalsobeslow,especiallyforlargedocuments.WithSimpleAPIforXML(SAX)parsers,theprogrammustcreateeventlistenersthatlistentoparsingeventsastheyoccur.XMLparserstendtobeabusedmoreoften.Heavy-dutyXMLparsingtoparseacomparativelysmallamountofdataXMLStreamingcanimproveperformance,especiallywhendealingwithlargeXMLdocuments.,XMLStreaming,ProvidesaneasyandintuitivewaytoparseandgenerateXMLdocumentsEnablesaprocedural,stream-basedhandlingofXMLdocumentsratherthanrequiringyoutowriteSAXeventhandlers,whichcangetcomplicatedwhenyouworkwithcomplexXMLdocumentsIsaJava-basedAPIforpullparsingXMLasopposedtopushparsingXMLpullparsersareknownfortheirsuperiorperformanceandlowmemoryfootprint.,SectionSummary,Inthissection,youlearnedabout:HibernateAJAXXMLStreaming,RoadMap,DesignPatternsAntiPatternsGeneralDesignTipsNewTechnologiesHSQLDatabase,Introduction,HSQLisanopensourcerelationaldatabaseenginewritteninJava.Itoffersalightweightandfastdatabaseengine,whichoffersbothin-memoryanddisk-basedtablesandsupportsembeddedandservermodes.ItincludestoolssuchasaminimalWebserver,in-memoryquery,andmanagementtools(canberunasapplets).ThelatestHSQLdatabasecanbedownloadedfrom.,Components,ThecomponentsoftheHsqldbJARpackageare:HSQLRDBMSHSQLJDBCdriverDatabaseManager(SwingandAbstractWindowToolkit(AWT)versions)Querytool(AWT)SQLtool(commandline)TheHSQLRDBMSandJDBCdriverprovidethecorefunctionality.,ServerModes,HSQLhasseveralservermodes,basedontheprotocolusedforcommunicationsbetweentheclientandserver.HsqldbServerHsqldbWebServerHsqldbServletIn-Process(Standalone)Memory-OnlyAdifferentsubprogramfromtheJARisusedtorunHSQLineachmode.,HSQLServerMode,Itisthepreferredwayofrunningadatabaseserverandthefastestone.Aproprietarycommunicationsprotocolisusedforthismode.ThecommandtorunHSQLinservermodefordatabasexdbisasfollows:,java-cp./lib/hsqldb.jarorg.hsqldb.Server-database.0mydb-dbname.0 xdb,HSQLWebServer,ThismodeisusedwhenaccesstothecomputerhostingthedatabaseserverisrestrictedtotheHTTPprotocol.ThismodeallowsJDBCclientstoconnectviaHTTP.ThecommandtoruntheHSQLinWebServermodefordatabasexdbisasfollows:,java-cp./lib/hsqldb.jarorg.hsqldb.WebServer-database.0mydb-dbname.0 xdb,HSQLDBServlet,hsqlServletusesthesameprotocolastheWebServer.Itisusedwhenaseparateservletengineorapplicationserverprovidesaccesstothedatabase.ThehsqlServletclass,inthehsqldb.jar,shouldbeinstalledontheapplicationservertoprovidetheconnection.Thedatabaseisspecifiedusinganapplicationserverproperty.,In-Process(Standalone)Mode,ThismoderunsthedatabaseengineaspartofanapplicationprograminthesameJVM.Formostapplications,thismodecanbefaster,asthedataisnotconvertedandsentoverthenetwork.Itisnotpossiblebydefaulttoconnecttothedatabasefromoutsidetheapplication.TheCommandtoconnecttoHSQLinthein-processmodeisasfollows:,Connectionc=DriverManager.getConnection(jdbc:hsqldb:file:testdb,“username,“password);,Memory-OnlyMode,Formemory-onlymode,thedatabaseisnotpersistentandexistsentirelyinrandomaccessmemory.Thismodeshouldbeusedonlyforinternalprocessingofapplicationdata,inappletsorcertainspecialapplications.Thismodeisspecifiedbythemem:protocol.ThecommandtoconnecttoHSQLinmemory-onlymodeisasfollows:,Connectionc=DriverManager.getConnection(jdbc:hsqldb:mem:aname,“username,“password);,HSQLDatabaseFiles,EachHSQLdatabaseconsistsofbetweentwotofivefiles,allnamedthesamebutwithdifferentextensions,locatedinthesamedirectory.Forexample,thedatabasenamedtestconsistsofthefollowingfiles:perties:Thepropertiesfilecontainsgeneralsettingsaboutthedatabase.test.script:Thescriptfilecontainsthedefinitionoftablesandotherdatabaseobjects,plusthedatafornon-cachedtables.test.log:Thelogfilecontainsrecentchangestothedatabase.test.data:Thedatafilecontainsthedataforcachedtables.test.backup:Thisprovidesdatabackup.,ConnectingtoaDatabase,OnceanHSQLDBserverisrunning,clientprogramscanconnecttoitusingtheHSQLDBJDBCdrivercontainedinhsqldb.jar.ThefollowingisanexampleJavacodetoconnecttothelocalserverrunningondefaultport9001.,Class.forName(org.hsqldb.jdbcDriver);Connectionc=DriverManager.getConnection(jdbc:hsqldb:hs