java JDBC 外文翻译 外文文献 英文文献.docx

java JDBC 外文翻译 外文文献 英文文献.docx

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javaJDBC外文翻译外文文献英文文献

原文一：

JavaProgrammingwithOracleJDBC：

Performance

Performanceisusuallyconsideredanissueattheendofadevelopmentcyclewhenitshouldreallybeconsideredfromthestart.Often,ataskcalled"performancetuning"isdoneafterthecodingiscomplete,andtheenduserofaprogramcomplainsabouthowlongittakestheprogramtocompleteaparticulartask.Thenetresultofwaitinguntiltheendofthedevelopmentcycletoconsiderperformanceincludestheexpenseoftheadditionaltimerequiredtorecodeaprogramtoimproveitsperformance.It'smyopinionthatperformanceissomethingthatisbestconsideredatthestartofaproject.

WhenitcomestoperformanceissuesconcerningJDBCprogrammingtherearetwomajorfactorstoconsider.ThefirstistheperformanceofthedatabasestructureandtheSQLstatementsusedagainstit.ThesecondistherelativeefficiencyofthedifferentwaysyoucanusetheJDBCinterfacestomanipulateadatabase.

Intermsofthedatabase'sefficiency,youcanusetheEXPLAINPLANfacilitytoexplainhowthedatabase'soptimizerplanstoexecuteyourSQLstatements.Armedwiththisknowledge,youmaydeterminethatadditionalindexesareneeded,orthatyourequireanalternativemeansofselectingthedatayoudesire.

Ontheotherhand,whenitcomestousingJDBC,youneedtoknowaheadoftimetherelativestrengthsandweaknessesofusingauto-commit,SQL92syntax,andaStatementversusaPreparedStatementversusaCallableStatementobject.Inthischapter,we'llexaminetherelativeperformanceofvariousJDBCobjectsusingexampleprogramsthatreporttheamountoftimeittakestoaccomplishagiventask.We'llfirstlookatauto-commit.Next,we'lllookattheimpactoftheSQL92syntaxparser.Thenwe'llstartaseriesofcomparisonsoftheStatementobjectversusthePreparedStatementobjectversustheCallableStatementobject.Atthesametimewe'llalsoexaminetheperformanceoftheOCIversustheThindriverineachsituationtoseeif,asOracle'sclaims,thereisasignificantenoughperformancegainwiththeOCIdriverthatyoushoulduseitinsteadoftheThindriver.Forthemostpart,ourdiscussionswillbebasedontimingdatafor1,000insertsintothetestperformancetableTESTXXXPERF.Thereareseparateprogramsforperformingthese1,000insertsusingtheOCIdriverandtheThindriver.

Theperformancetestprogramsthemselvesareverysimpleandareavailableonlinewiththerestoftheexamplesinthisbook.However,forbrevity,I'llnotshowthecodefortheexamplesinthischapter.I'llonlytalkaboutthem.Althoughtheactualtimingvalueschangefromsystemtosystem,theirrelativevalues,orratiosfromonesystemtoanother,remainconsistent.ThetimingsusedinthischapterweregatheredusingWindows2000.Usingobjectivedatafromtheseprogramsallowsustocometofactualconclusionsonwhichfactorsimproveperformance,ratherthanrelyingonhearsay.

I'msureyou'llbesurprisedattherealityofperformancefortheseobjects,andIhopeyou'llusethisknowledgetoyouradvantage.Let'sgetstartedwithalookatthetestingframeworkusedinthischapter.

ATestingFramework

Forthemostpart,thetestprogramsinthischapterreportthetimingsforinsertingdataintoatable.IpickedanINSERTstatementbecauseiteliminatestheperformancegainofthedatabaseblockbuffersthatmayskewtimingsforanUPDATE,DELETE,orSELECT.

Thetesttableusedintheexampleprogramsinthischapterisasimplerelationaltable.IwantedittohaveaNUMBER,asmallVARCHAR2,alargeVARCHAR2,andaDATEcolumn.TableTESTXXXPERFisdefinedas:

createtableTestXXXPerf（

idnumber,

codevarchar2（30）,

descrvarchar2（80）,

insert_uservarchar2（30）,

insert_datedate）

tablespaceuserspctfree20

storage（initial1Mnext1Mpctincrease0）;

altertableTestXXXPerf

addconstraintTestXXXPerf_Pk

primarykey（id）

usingindex

tablespaceuserspctfree20

storage（initial1Mnext1Mpctincrease0）;

Theinitialextentsizeusedforthetablemakesitunlikelythatthedatabasewillneedtotakethetimetoallocateanotherextentduringtheexecutionofoneofthetestprograms.Therefore,extentallocationwillnotimpactthetimings.Giventhisbackground,youshouldhaveacontexttounderstandwhatisdoneineachsectionbyeachtestprogram.

Auto-Commit

Bydefault,JDBC'sauto-commitfeatureison,whichmeansthateachSQLstatementiscommittedasitisexecuted.IfmorethanoneSQLstatementisexecutedbyyourprogram,thenasmallperformanceincreasecanbeachievedbyturningoffauto-commit.

Let'stakealookatsomenumbers.Table19-1showstheaveragetime,inmilliseconds,neededtoinsert1,000rowsintotheTESTXXXPERFtableusingaStatementobject.Thetimingsrepresenttheaveragefromthreerunsoftheprogram.Bothdriversexperienceapproximatelya