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VSAM Buffer.

 
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sprakash1279

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Joined: 18 Apr 2011
Posts: 3
Location: India

PostPosted: Thu May 12, 2011 3:49 pm    Post subject: VSAM Buffer.
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Hi,

I have a VSAM file reading the record by RANDOM read. The below are the values from the LISTCAT. After introducing this VSAM file in the processing, the Job is started runnning for 3 hours, which was completed in 5 to 10 mins earlier.

The VSAM file has only 500 records in it. I tried having AMP='BUFNI=20' but didnt reduce the run time. What would be the optimum Buffer value I could add to improve the performace of the Job ? Many thanks.

Code:


Total Index Records   HURBA   CISIZE   CIs per CA
1                    691200     5,120      135

BUFSPACE-----------11264     CISIZE--------------5120
EXCPEXIT----------(NULL)     CI/CA----------------135
INDEXED       NOWRITECHK     NOIMBED       NOREPLICAT

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Bill O'Boyle

CICS Moderator


Joined: 14 Jan 2008
Posts: 2502
Location: Atlanta, Georgia, USA

PostPosted: Thu May 12, 2011 4:01 pm    Post subject: Reply to: VSAM Buffer.
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In the SELECT, ensure that you're specifying ACCESS IS RANDOM rather than ACCESS IS DYNAMIC.

This may help....

Bill
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sprakash1279

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Joined: 18 Apr 2011
Posts: 3
Location: India

PostPosted: Thu May 12, 2011 4:07 pm    Post subject:
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Hi Bill,

Yes. The file control is mentioned correctly.

Code:


SELECT TNBSCOS  ASSIGN       TO TNBSCI1           
                ORGANIZATION IS INDEXED           
                ACCESS       IS RANDOM             
                RECORD KEY   IS COST-KEY OF TNBSC01
                FILE STATUS  IS WS-FILE-STATUS.   



File processing Status :

Code:


 Command ===>                                                                   
                                                                               
      System: S0E5             Jobname: JSBDKV17        Stepname: JS010010     
    Duration: 00:01:11                                                         
     DD Name: TNBSCI1          DS Name: JSSBSA.LIVE.TNBSCOS                     
                           Data Source: JOB CTL BLOCKS                         
 Status   Type Format  Access   Opts            LSR  Misc                       
 CLSD-IN  KSDS         NSR      DIR   KEY                                       
                                                                               
 DATA:------------------------------------------------------------------------ 
  CIFR  CAFR   CISP   CASP   CISZ   CI-CA   Keyln  Keyps  Maxlr                 
 10     0      0      0      5,120  135     6      0      43                   
                                                                               
 EXTNT EXCPs      Reccount     Retrved     Updated     Deleted     Insrted     
 1     20,776     303          0           0           0           0           
                                                                               
 INDEX:----------------------------------------------------------------------- 
  CIFR   CAFR  CISP       CASP  CISZ    CA     LVL    EXT Reccnt    EXCP       
 0       0     0          0     1,024   33     1      1   1         20,775     

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Nic Clouston

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Joined: 10 May 2007
Posts: 1825
Location: UK

PostPosted: Thu May 12, 2011 4:08 pm    Post subject:
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How many times is the file accessed in each run? It may be more efficient to load it to a COBOL table. Another way to improve efficiency is to check to see if the key being used to access the file is the same as for the previous access in which case you do not need to access it again as the data would be current in your program.
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Bill Woodger

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Joined: 09 Mar 2011
Posts: 7315

PostPosted: Thu May 12, 2011 4:26 pm    Post subject: Reply to: VSAM Buffer.
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Your EXCP counts for data and index are surprisingly close. In addition to Nic, is your input file in key order? If not, buffers will be filled, only to be thrown away, as a lower key arrives. More buffer space, more wasted io.

For the size of your file, Nic's Cobol table sounds a good idea. Load it up, occurs depending on, search all, with Nic's check-for-previous-search as well.

Or process in key order, even if you have to re-sequence later.

Or if it has to be like you have it, try making only one buffer.
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Robert Sample

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Joined: 06 Jun 2008
Posts: 8117
Location: East Dubuque, Illinois, USA

PostPosted: Thu May 12, 2011 4:32 pm    Post subject:
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Quote:
What would be the optimum Buffer value I could add to improve the performace of the Job ?
Your last post indicates there is 1 index level -- so providing anything more than 2 index buffers will not result in performance improvements, and could degrade performance (the system does have to manage however many buffers you tell it to use). You should add more data buffers, however, since the minimum is usually not enough.

I think the basic problem is you have started with an invalid assumption and are leaping to invalid conclusions thereby. You are assuming -- on no evidence that I can see -- that VSAM buffering is your problem. It is much more likely that you have a program logic problem that is causing the additional elapsed time for your job. For example, if you open the file, read a record, close the file and repeat this over and over -- that alone could add a LOT of time to your run. Of course, there are many other potential problems -- but you should be looking at your code around the VSAM file access, not changing system parameters, to fix the problem.
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