VASM面试题.docx

VASM面试题.docx

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VASM面试题

VirtualStorageAccessMethod（VSAM）

Q1）WhatarethetypesofVSAMdatasets?

A1）Entrysequenceddatasets（ESDS）,keysequenceddatasets（KSDS）andrelativerecorddataset（RRDS）.

Q2）HowarerecordsstoredinanESDS,entrysequenceddataset?

A5）Theyarestoredwithoutrespecttothecontentsoftherecordsandintheorderinwhichtheyareincludedinthefile.

Q3）WhatisaCI,controlinterval?

（文章来源：

http:

//www.newcoin.info）

A3）AcontrolintervalistheunitofinformationthatVSAMtransfersbetweenvirtualandauxiliarystorage.

Q4）Whatarethedistinctivefeaturesofaksds,keysequenceddataset?

A4）Theindexandthedistributedfreespace.

Q5）WhatisaCA,controlarea?

A5）Agroupofcontrolintervalsmakesupacontrolarea.

Q6）Whatisasequenceset?

A6）ThisisthepartoftheindexthatpointstotheCAandCIoftherecordbeingaccessed.

Q7）Whatistheindexset?

A7）Thisistheotherpartoftheindex.Ithasmultiplelevelswithpointersthatultimatelyreachtothesequenceset.

Q8）Whatisacluster?

A8）Aclusteristhecombinationoftheindex,sequencesetanddataportionsofthedataset.Theoperatingsystemgivesprogramaccesstothecluster,ie.toallpartsofthedatasetsimultaneously.

Q9）Whatisthecatalog?

Q9）Thecatalogcontainsthenamesofalldatasets,VSAMandnon-VSAM.Itisusedtoaccessthesedatasets.

Q10）Whatisanalternateindex?

Q10）AnAIXisafilethatallowsaccesstoaVSAMdatasetbyakeyotherthantheprimaryone.

Q11）Whatisapath?

Q11）Apathisafilethatallowsyoutoaccessafilebyalternateindex–thepathprovidesanassociationbetweentheAIXandthebasecluster.

Q12）Whatistheupgradeset?

Q12）TheupgradesetisthelistofallAIXesthatVSAMmustmaintainforaspecificbasecluster,sothatwhendatainthebaseclusterisupdated,theAIXfilesarealsoupdated.

Q13）Whatisfreespace?

Q13）FreespaceisreservedwithinthedatacomponentofaKSDStoaccommodateinsertingnewrecords.

Q14）WhatisaVSAMsplit?

Q14）Ifthereisn’tenoughspaceinthecontrolintervalVSAMperformsacontrolintervalsplitbymovingsomerecordstothefreecontrolintervals.Ifthereisn’tafreecontrolintervalVSAMperformsacontrolareasplitbyallocatinganewcontrolareaandmovinghalfofthecontrolintervalstoit.

Q15）Whatisthebasecluster?

Q15）ThebaseclusterconsistsofthedatacomponentandtheindexcomponentfortheprimaryindexofaKSDS.

Q16）Doprimarykeyvalueshavetobeunique?

Doalternatekeyvalueshavetobeunique?

Q16）Primarykeyvaluesmustbeunique;alternatekeyvaluesneednotbe.

Q17）IntheCOBOLSELECTstatementwhatistheORGANIZATIONforaKSDS?

Q17）TheORGANIZATIONisINDEXED.

Q18）IntheCOBOLSELECTstatementforaKSDSwhatarethethreepossibilitiesforACCESS?

Q18）ACCESScanbeSEQUENTIAL,RANDOMorDYNAMIC.

Q19）WhatistheCOBOLRECORDKEYclause?

Q19）TheRECORDKEYintheSELECTclauseidentifiesthefilesprimarykeyasitwillbeknowntotheprogram.

Q20）WhatisthepurposeoftheFILESTATUSclauseintheSELECTstatement?

Q20）TheFILESTATUSfieldidentifiesthefieldthatVSAMusestoprovideinformationabouteachI/Ooperationforthefile.

Q21）IfyouwishtousetheREWRITEcommandhawmusttheVSAMfilebeopened?

Q21）ItmustbeopenedasI/O.

Q22）ExplainthemeaningandsyntaxfortheSTARTcommand.

Q22）TheSTARTcommandisusedreadotherthanthenextVSAMrecord.AvaluemustbemovedintotheRECORDKEY.TheKEYclauseisoptional,butitcanbeusedtospecifyarelational（equal,lessthan,etc.）operator.

Q23）Whatisthemeaningofdynamicprocessing?

Q23）It’srarelyused.ItmeansoneprogramusesbothsequentialandrandomprocessingforaVSAMKSDSfile.

Q24）NamesomecommonVSAMerrorconditionsandcodes.

Q24）Theyareendoffile（10）,duplicatekey（22）,recordnotfound（23）,VSAMlogicerror（90）,openproblem（92）andspaceproblem（93）.

Q25）WhatistheVSAM-codefield?

Q25）ItisaCOBOLIIenhancementtoVSAMbatchprocessingexpandingtheFILESTATUSfield.ItisdefinedinWORKING-STORAGEasasixbytegroupitemwiththreetwobyteelements,thenormalreturncode,thefunctioncodeandthefeedbackcode.

Q26）WhatisaVSAMslot?

Q26）Arelativerecorddataset（RRDS）consistsofaspecifiednumberofareascalledslots.Eachslotisidentifiedbyarelativerecordnumber（RRN）whichindicatesitsrelativepositioninthefile.

Q27）WhatistheutilityprogramcloselyassociatedwithVSAM?

Q27）IDCAMS,theaccessmethodservicesutility.

Q28）ThereareatleastsevenIDCAMScommands;nameandexplaineachofthem?

.

Q28）ALTERmodifiesinformationforacatalog,alternateindex,clusterorpath.BLDINDEXbuildsthealternateindex,ofcourse.DEFINEisusedforALTERNATEINDEX,CLUSTERorPATH.DELETEremovesthecatalogentryforacatalog,cluster,alternateindexorpath.LISTCATlistsinformationaboutthedataset.PRINTprintsthedatasetcontents.REPROcopiesrecordsfromonefiletoanother.

Q29）WhatarethethreelevelsofdefinitionfortheVSAMDEFINE?

Q29）TheyareDEFINECLUSTER,DATAandINDEX.（文章来源：

http:

//www.newcoin.info）

Q30）WhatisthesignificanceoftheSHAREOPTIONSparameter?

Q30）ItspecifieshowthefilemaybesharedbetweenjobsandbetweenbatchandCICSenvironments.

Q31）WhatisthemeaningoftheDEFINEMODELparameter?

Q31）ItspecifieswhetherDanielaPestovaorYamila–oops!

Wrongmodels!

TheMODELparameterallowsyoutomodelyourclusterbymodelingitafteranexistingcluster.

Q32）WhatisFileStatusinVSAM?

Q32）TheFILESTATUSclauseoftheFILE-CONTROLparagraphallowsforeachfiletobeassociatedwithafilestatuskey（i.e.,the2-characterdataitemspecifiedintheFILESTATUSclause）.IftheFILESTATUSclauseisspecifiedforagivenfile,avalueindicatingthestatusofeachI/Ooperationagainstthatfileisplacedintheassociatedfilestatuskey.ThisvalueisstoredinthefilestatuskeyassoonastheI/Ooperationiscompleted（andbeforeexecutionofanyEXCEPTION/ERRORdeclarativeorINVALIDKEY/ATENDphraseassociatedwiththeI/Orequest）.

Note:

ThiselementmaybehavedifferentlywhentheCMPR2compileroptionisused.Thefilestatuskeyisdivided

intotwostatuskeys:

thefirstcharacterisknownasfilestatuskey1;thesecondcharacterisfilestatuskey2.

Q33）What’saLDS（LinearDataSet）andwhat’situsedfor?

Q33）LDSisaVSAMdatasetinnameonly.Ithasunstructured4k（4096bytes）fixedsizeCI’swhichdonotcontaincontrolfieldsandthereforefromVSAM’sstandpointtheydonotcontainanylogicalrecords.Thereisnofreespace,andnoaccessfromCobol.CanbeaccessedbyDB2andIMSfastpathdatasets.LDSisessentiallyatableofdatamaintainedondisk.The‘tableentries’mustbecreatedviaauserprogramandcanonlybelogicallyaccessedviaauserprogram.Whenpassed,theentireLDSmustbemappedintostorage,andthendataisaccessedviabaseanddisplacementtypeprocessing.

Q34）WhatisIDCAMS?

Q34）IDCAMSistheAccessMethodServicesprogram.YouruntheIDCAMSprogramandsupplyAMScommandsthruSYSIN.（examplesofAMScommandsareDELETE,DEFINE,REPROetc..）.

Q35）CanAMScommandsberunfromtheTSOprompt?

Q35）Yes

Q36）SyntaxofAMSmodalcommands?

（文章来源：

http:

//www.newcoin.info）

Q36）Note:

thesecanbeusedonlyunderIDCAMSandnotfromtheTSOprompt.

IFLASTCC（orMAXCC）>（or<,=etc..）value-

THEN-

DO-

commandset（suchasDELETE,DEFINEetc..）

ELSE-

DO-

commandset

LASTCC–Conditioncodefromthelastfunction（suchasdelete）executed

MAXCC–Maxconditioncodethatwasreturnedbyanyoftheprevfunctions

SETisalsoavalidAMScommand.SETLASTCC（orMAXCC）=value

Themaximumconditioncodeis16.Acondcodeof4indicatesawarning.Acondcodeof8isusuallyencounteredonaDELETEofadatasetthatisnotpresent.

Q37）UnderIDCAMS,multiplefunctionscanbeexecuted,eachofwhichreturnsacondcode.Whatwillbetheconditioncodereturnedtotheoperatingsystem?

Q37）ThemaximumconditioncodegeneratedisreturnedastheconditioncodeoftheIDCAMSstep.

Q38）WhatisControlInterval,ControlArea?

Q38）ControlIntervalisanalogoustoaphysicalblockforQSAMfiles.ItistheunitofI/O.Mustbebetween512bytesto32k.Usuallyeither2Kor4K.Alargercontrolintervalincreasesperformanceforsequentialprocessingwhilethereverseistrueforrandomaccess.UnderCICSwhenarecordislocked,theentireCIgetslocked.

ControlAreaisagroupofcontrolintervals.CAisusedduringallocation.CAsizeiscalculatedbasedonthe

allocationtype（cyl,tracksorrecords）andcanbemaxof1cylinder

Q39）WhatisFREESPACE?

Q39）CodedintheDEFINEasFREESPACE（cica）whereciisthepercentageofeachcontrolintervaltobeleftfreeforinsertions,caisthepercentageofcontrolintervalsineachcontrolareatobeleftempty.

Q40）HowdoyoudecideonoptimumvaluesforCI,FREESPACEetc…?

Q40）CIsizeshouldbebasedonrecordlength,typeofprocessing.UsuallyCIis4K.Ifrecordlengthislarger（>1K）,chose6Kor8K.FREESPACEshouldbelargeifmorenumberofinsertionsareenvisaged.Usualvaluesare（2020）whenheavyupdatesareexpected.CIsizecanbecalculated.

Q41）WouldyouspecifyFREESPACEforanESDS?

Q41）No.BecauseyoucannotinsertrecordsinanESDS,alsowhenyourewritearecord,itmustbeofthesamelength.Thusputtinganyvalueforfreespacedoesnotmakeanysense.

Q42）WhatisSHAREOPTS?

Q42）SHAREOPTSisaparameterintheDEFINEandspecifieshowanobjectcanbesharedamongusers.ItiscodedasSHAREOPTS（ab）,whereaisthecrossregionshareoptioniehowtwoormorejobsonasinglesystemcansharethefile,whilebisthecrosssy