This sectiondiscusseshowto sizethefollowingtypesofDASD-onlylogstream:
v
TheCICSprimaryandsecondarysystem logstreams v Forwardrecoverylogs
v Userjournals andautojournals.
Sizing DFHLOG
For theCICSprimarysystem logstream(DFHLOG), itisimportantto:
v Minimizetheamount ofdatathat isoffloaded tosecondarystorage:
TheMVSsystemloggerbeginstheoffloadprocesswhenthehigh offload threshold(HIGHOFFLOAD)of thelogstreamisreached.Theoffloadprocess consistsoftwo steps:
1. TheMVSloggerphysicallydeletes thedata inthelogstreamthathasbeen markedfordeletion bytheCICSlog-taildeletionprocess.
2. TheMVSloggercalculateshow muchdataneedstobeoffloadedto secondarystorage,basedonthedifference betweenHIGHOFFLOADand LOWOFFLOAD,lesstheamountofdata thathasbeendeletedsincethelast offloadevent.
Tominimizetheamountof dataoffloadedfromtheCICSprimarysystemlog,you must:
– Defineasuitably-sizedstagingdataset.For advice,see“Recommendations”
onpage 132.
//DEFLOGS JOB ...
//LOGDEFN EXEC PGM=IXCMIAPU
//STEPLIB DD DSN=SYS1.MIGLIB,DISP=SHR //SYSPRINT DD SYSOUT=* //* only -- substitute values appropriate for your environment. *
//* *
//******************************************************************
//SYSIN DD *
DATA TYPE(LOGR) REPORT(NO)
DEFINE LOGSTREAM NAME(sysname.DFHLOG.MODEL)
MODEL(YES)
DASDONLY(YES)
MAXBUFSIZE(64000)
STG_SIZE(3000)
LOWOFFLOAD(40) HIGHOFFLOAD(80)
DEFINE LOGSTREAM NAME(sysname.DFHSHUNT.MODEL)
MODEL(YES)
DASDONLY(YES)
MAXBUFSIZE(64000)
STG_SIZE(500)
LOWOFFLOAD(40) HIGHOFFLOAD(80)
Figure20.ExamplemodeldefinitionsforDASD-onlysystemlogstreams.Thevalue sysnameisthesysidoftheMVSimageinwhichtheCICSregionorregionsarerunning.
Note: It ispossibleto alterthesizeof astagingdatasetwithout deletingthe logstream.Todothis, usetheUPDATELOGSTREAMrequestofthe MVS IXCMIAPUutilityto changethevalueof theSTG_SIZE
parameter.
– Ensurethatthelog-taildeletionprocess isworkingeffectively.For detailed informationaboutthelogtaildeletionprocess,seetheCICSRecoveryand RestartGuide.
v
Avoid“staging-data-set-full”events:
Astaging-data-set-fulleventoccurswhenalogstream’sstaging dataset becomesfullbeforetheoffloadingofdatahascompleted.
Foradvice onmonitoringandavoidingstaging-data-set-fullevents,seetheCICS PerformanceGuide.
Sizing DFHSHUNT
It isimportanttosizethesecondarysystemlogstream(DFHSHUNT)to avoid staging-data-set-full events.However,it isnormalfor somedata tobeoffloaded fromDFHSHUNTto secondarystorage.
Sizing general logs
It isimportanttosizeforwardrecoverylogs,userjournals,andautojournalstoavoid staging-data-set-full events.However,becauseCICSdoesnotdeletedatafrom theselogstreams,it isnormalfor datatobeoffloadedto secondarystorage.
Recommendations
Table6 summarizeshow youshoulddecideonthevalues forvariousattributeson thelogstreamdefinition,andsystemdefinition.
Table6.Howtodecideonthevaluesofattributes
Facility Attribute Recommendation
Primarysystemlog stream(DFHLOG)
HIGHOFFLOAD 80
LOWOFFLOAD UseDFHLSCUortheformulaonpage
“LOWOFFLOADcalculations”onpage134.
MAXBUFSIZE 64000
STG_SIZE UseDFHLSCUortheformulaonpage“Staging DSsizecalculation”onpage134.
Secondarysystem
STG_SIZE UseDFHLSCUortheformulaonpage“Staging datasetsizecalculation”onpage129.
CICSsystem AKPFREQ 4000
Note: Startupmay takelongerthanyou experiencedwhenusingearlierreleases.
Thisisdueinpartto theallocationandformattingof thestagingdatasets.
Theincreasedtimethatstartuptakesisdependentonsuchthingsas:
v Size ofstagingdataset(STG_SIZE) 132 CICSTSforz/OS: InstallationGuide
v DASDspeed v DASDcontention
Itcanbereducedbyavoidingtheuseof unnecessarilylarge stagingdata sets.
The log stream sizing utility, DFHLSCU
If youaremigratingfromCICS/ESA 3.3orCICS/ESA 4.1,youarestrongly recommendedto usetheCICS-supplied utilityprogram,DFHLSCU,tohelpyou defineyourDASD-onlylogstreams. DFHLSCUtakesasinput“old-style”(pre-CICS TransactionServerfor OS/390,Version1 Release1-format)journalrecords,and analyzesthem toproducea samplelogstreamdefinitioncontaining suggested values for:
DASDONLY(YES)
Specifiesthatthislogstreamisnottobeassociatedwithacouplingfacilitylist structure, butisto useDASD-onlylogging.If youspecifyDASDONLY(YES), youcannotuse theSTRUCTNAME(log_structure_name)keyword.Thedefault isDASDONLY(NO).
HIGHOFFLOAD(high_offload)
Specifiesthepointinprimarystorage,asapercentageofspaceconsumed,at which theMVS systemloggerstartsitsoffloadprocess.
LOWOFFLOAD(low_offload)
Specifiesthepointinprimarystorage,asapercentageofspaceconsumed,at which theMVS systemloggerstopsoffloadingdatato secondarystorage.
MAXBUFSIZE(max_bufsize)
Specifiesthesize,inbytes,of thelargestblockof datathatcanbewritten to thelogstream.Thevaluemust beintherange1–65532.Thedefaultvalueis 65532.
STG_SIZE(stg_size)
Specifies,asanumberof 4Kblocks,thesizeofthestagingdatasetfor thelog stream.ADASD-onlylogstream,bydefinition,alwaysusesastagingdataset aspartofitsprimarystorage.
If youdonotspecifySTG_SIZEfor aDASD-onlylogstream,theMVS system loggerdoesoneof thefollowing,intheorderlisted,to allocatespacefor staging datasets:
1. UsestheSTG_SIZE ofthelogstreamspecified ontheLIKEparameter,if LIKE isspecified
2. UsesthesizedefinedintheSMS dataclassforthestagingdatasets 3. If SMSisnotavailable,usesdynamicallocationrules forallocatingdata
sets.
For moreinformationaboutmanagingstagingdatasets forDASD-onlylog streams, seetheSettingUpa Sysplexmanual.
For detailsonhowto useDFHLSCU,seetheCICSOperationsandUtilities Guide.
If DFHLSCU is inappropriate for use in your environment
If itisinappropriatefor youtouseDFHLSCUto helpyousizeyourlogstreams (perhapsyou havenoCICSVersion4 orVersion3journalrecordstouseasinput to DFHLSCU,oryouarecapacityplanningfor newapplications),thefollowing sectionswillhelpyouto calculateyourspacerequirements.
v LOWOFFLOAD v STG_SIZE
You mustbase yourcalculationsonthejournalingrequirementsof your applications.This providesthestartingpointfor thefollowingformulae.
Primarysystemlog(DFHLOG): YoucancalculateLOWOFFLOADfor DFHLOG usingthefollowingformula:
LOWOFFLOAD = (trandur * 90) / (akpintvl + trandur) + 10 (where RETPD=0 specified) or
LOWOFFLOAD = (trandur * 90) / (akpintvl + trandur) (where RETPD=dddd specified) where:
v akpintvlistheinterval betweenactivitykeypoints.It canbecalculated as follows:
akpintvl = AKPFREQ / ( (N1 * R1) + (N2 * R2) + (Nn * Rn) ) where:
– N1, N2.... Nnis thetransaction ratefor each transaction(transactions per second).
– R1, R2.... Rnis thenumberof log recordswritten byeach transaction.
v tranduristheexecutiontime(betweensyncpoints)of thelongest-running transactionthatrunsaspartofthenormalworkload.
Ifthisduration islongerthanakpintvlvalue,youcaneither:
– IncreasethevalueofAKPFREQ,soincreasingthevalueof akpintvl(aslong asthis doesnotresultinanunacceptablylargestagingdata setsize).
– Changetheapplicationlogicto causemorefrequentsyncpoints.
– Calculateastaging datasetsizebasedonashortertransactionduration,and acceptthatoffloadingto secondarystorageoccurswhenthelong-running transactionisused.
You cancalculateSTG_SIZEfor DFHLOGusingthefollowingformula:
Staging DS size = (AKP duration) * No. of log writes per second for system log (no. of 4k blocks)
where AKP duration = (CICS TS 390 AKPFREQ)/(No. buffers per second)
Thevaluesfor thenumberof logwritespersecondandbufferputspersecondcan betakenfromyourCICS/ESA 4.1statistics.(Thevalueforlogwritespersecond should notexceed 30.)