java JDBC 外文翻译 外文文献 英文文献Word文档下载推荐.docx

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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

Theinitialextentsizeusedforthetablemakesitunlikelythatthedatabasewillneedtotakethetimetoallocateanotherextentduringtheexecutionofoneofthetestprograms.Therefore,extentallocationwillnotimpactthetimings.Giventhisbackground,youshouldhaveacontexttounderstandwhatisdoneineachsectionbyeachtestprogram.

Auto-Commit

Bydefault,JDBC'

sauto-commitfeatureison,whichmeansthateachSQLstatementiscommittedasitisexecuted.IfmorethanoneSQLstatementisexecutedbyyourprogram,thenasmallperformanceincreasecanbeachievedbyturningoffauto-commit.

Let'

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