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BLKSIZE in COBOL and DCB Parameter


IBM Mainframe Forums -> JCL & VSAM
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baramesh

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Joined: 20 May 2008
Posts: 25
Location: bangalore

PostPosted: Sun Jun 29, 2008 5:23 pm
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Hi forum,


I have a confusion on how the BLKSIZE is determined.


In SELECT clause it s coded as

BLOCK CONTAINS 0 RECORDS

And DCB parameter contains BLKSIZE=800.

Which block size will be considered here.whether sys determines the effective size or the jcl value is taken.

Please suggest me.
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Craq Giegerich

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Joined: 19 May 2007
Posts: 1512
Location: Virginia, USA

PostPosted: Sun Jun 29, 2008 8:33 pm
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I hope you have block contains 0 records in the FD and not in the select.

From the Enterprise COBOL Language Reference.

BLOCK CONTAINS 0 can be specified for QSAM files. If BLOCK CONTAINS 0 is specified for a QSAM file, then:

The block size is determined at run time from the DD parameters or the data set label. If the RECORD CONTAINS 0 CHARACTERS clause is specified, and the BLOCK CONTAINS 0 CHARACTERS clause is specified (or omitted), the block size is determined at run time from the DD parameters or the data set label of the file. For output data sets, with either of the above conditions, the DCB used by Language Environment will have a zero block size value. If you do not specify a block size value, the operating system might select a System Determined Block Size (SDB). See the operating system specifications for further information on SDB.
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baramesh

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Location: bangalore

PostPosted: Mon Jun 30, 2008 12:05 pm
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Opps Please accept my apologies.And thanks for your time, answering the question
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manojtyagi_09

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Joined: 30 Oct 2006
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PostPosted: Mon Jun 30, 2008 1:55 pm
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Its always better to write Block contains 0 records/characters in COBOl program. So that u can specify the BLKSIZE in JCL.

Supppose there is a requiremet to change the BLKSIZE due to change in LRECL this will cause only change in BLKSIZE in JCL. if you mention BLOCK contains N records in COBOL program. then it is required to match with BLKSIZE in JCL also it wud be required to change COBOL + JCL both.
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robertovon

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Joined: 26 Jun 2008
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Location: San Antonio, Texas, USA

PostPosted: Mon Jun 30, 2008 9:34 pm
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It will use 800.
If you code BLKSIZE=0 in your DCB, the system will dtermine the most efficient block size for space utilization.
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