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Why BUFNO is used for output datasets

 
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sravani

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Joined: 17 Jul 2005
Posts: 3

PostPosted: Tue Aug 16, 2005 7:59 pm    Post subject: Why BUFNO is used for output datasets
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Hi,

My JCL has the following statements. Can anyone tell me why BUFNO is used for output datasets?

//SORTOUT DD DSN=&&TEMP1,BUFNO=29,
// DISP=(NEW,PASS,DELETE),
// SPACE=(CYL,(1500,1000),RLSE,,ROUND),

Thanks,
Sravani
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withnams

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Joined: 06 Jul 2005
Posts: 26
Location: Chennai

PostPosted: Tue Aug 16, 2005 8:52 pm    Post subject:
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It perhaps means the number of buffers alloacted for that dataset.
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ironmike

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Joined: 07 Aug 2005
Posts: 33

PostPosted: Wed Aug 17, 2005 7:57 am    Post subject:
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BUFNO= is the number of buffers that will be used for buffering output for that data set. The example you coded appears to be for a sequential file. Increasing the number of buffers can improve performance if QSAM is used for writing to an output sequential file. Your example is for a SORTOUT DD, so the program writing to the file may be the SORT; SORT probably used BSAM or EXCP to write to this file, in which case SORT is probably doing intelligent buffer management and the BUFNO=29 may be ignored; if your program and not the SORT is writing to the file out of a SORT exit (e.g., the SORT E35 exit), then your program may be using QSAM and bumping up BUFNO can speed up the output process.

Here's a quote from IBM's DFSMS Using Data Sets manual:
Quote:
In QSAM, the value of BUFNO determines how many buffers will be chained together before I/O is initiated...When enough buffers are available for reading ahead or writing behind, QSAM attempts to read or write those buffers in successive revolutions of the disk.


Default BUFNO for a sequential, non-SYSOUT file is five.

Basically, if you've got no virtual storage constraints, large BUFNO = goodness! icon_biggrin.gif
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mmwife

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Joined: 30 May 2003
Posts: 1592

PostPosted: Thu Aug 18, 2005 6:54 am    Post subject:
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DFSORT and Syncsort calculate and use their own BUFNO params for I/P and O/P.

Those supplied in the JCL are ignored.
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