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Regarding FILE ACCESS MODES

 
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rockish

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Joined: 05 Jun 2009
Posts: 185
Location: Planet Earth

PostPosted: Tue Jun 08, 2010 1:19 am    Post subject: Regarding FILE ACCESS MODES
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I am not sure if this has been discussed already in this forum or not. I tried searching for a while but couldn't get the information that I exactly needed and hence posting it here.

I have a cobol program which reads a VSAM File randomly (key based). This VSAM is currently declared as RANDOM in the program. I remember reading somewhere that the DYNAMIC access is faster for RANDOM access. I tried testing the difference (CPU/Elapsed time) between the two, but I have not got any high volume production like files to do the test yet. In the mean time, thought of raising this query in here.

Any help to clarify the performance of various file access modes in COBOL would be really appreciated :-)
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CICS Guy

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Joined: 18 Jul 2007
Posts: 2150
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PostPosted: Tue Jun 08, 2010 2:25 am    Post subject:
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Access modes
Sequential-access
mode Allows reading and writing records of a file in a serial manner; the order of reference is implicitly determined by the position of a record in the file.
Random-access
mode Allows reading and writing records in a programmer-specified manner; the control of successive references to the file is expressed by specifically defined keys supplied by the user.
Dynamic-access
mode Allows the specific input-output statement to determine the access mode. Therefore, records can be processed sequentially or randomly or both.
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Bill O'Boyle

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Joined: 14 Jan 2008
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PostPosted: Tue Jun 08, 2010 2:38 am    Post subject: Reply to: Regarding FILE ACCESS MODES
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I've found that when you're performing RANDOM Read's only, that ACCESS IS RANDOM is the better way to go, together with adequate buffering.

Generally, ACCESS IS DYNAMIC is used when you're jumping all over the file, using START, READNEXT, READ, DELETE, etc....

Bill
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Robert Sample

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Joined: 06 Jun 2008
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PostPosted: Tue Jun 08, 2010 4:12 am    Post subject:
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If you're doing pure key-based reads of the file, ACCESS IS RANDOM should be slightly better than ACCESS IS DYNAMIC for performance. How much better? I don't know -- but it would probably take a couple million reads to add up to enough difference to notice. Just make sure you have plenty of index buffers and some data buffers assigned to the file!
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rockish

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PostPosted: Tue Jun 08, 2010 6:59 pm    Post subject:
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Thanks a lot all for your suggestions. I will also test them and try to publish the results here.
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