JCL - What is AMP parameter and its use e.g. AMP='BUFNI=10,BUFND=10' means what?

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What is AMP parameter and its use
e.g. AMP='BUFNI=10,BUFND=10' means what?

Total Answers and Comments: 5

Last Update: February 18, 2009 Asked by: Phinix

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Submitted by: ameer

This parameter can be used to request the buffer space for the datasets usually VSAM datasets. when the datasets are accessed they are accessed only in terms of blocks for example when accessing a record from a dataset, the record is read from a block and when all the records from the block are read then the next block is accessed and so on. so as to place these blocks we require buffers which are specified using this parameter. here BUFNI will hold the Index part and BUFND will hold the data part of the VSAM file.

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vipin_sharma0383

April 15, 2008 07:14:18

nisanth_ts

Member Since: April 2008 Contribution: 1

RE: What is AMP parameter and its use e.g. AMP='BUFNI=10,BUFND=10' means what?

hi .

AMP parameter is used to specify the buffer space.BUFNI means the number of index buffers and BUFND is the number of data buffers.

syntax for specifying buffer space is

//buf dd .....AMP ('BUFND 10 BUFNI 10')

i hope you are clear with this.

Nisanth T.S
Bangalore

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April 18, 2008 04:48:01

Mazhar9

Member Since: December 2007 Contribution: 7

RE: What is AMP parameter and its use e.g. AMP='BUFNI=10,BUFND=10' means what?

Nishanth Well thanks.

But why do we need to supply this infomation? Any idea? Please suggest

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June 04, 2008 03:21:34

ameer

Member Since: June 2008 Contribution: 1

RE: What is AMP parameter and its use e.g. AMP='BUFNI=10,BUFND=10' means what?

This parameter can be used to request the buffer space for the datasets usually VSAM datasets. when the datasets are accessed they are accessed only in terms of blocks for example when accessing a record from a dataset the record is read from a block and when all the records from the block are read then the next block is accessed and so on. so as to place these blocks we require buffers which are specified using this parameter. here BUFNI will hold the Index part and BUFND will hold the data part of the VSAM file.

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Overall Rating: +1

October 21, 2008 06:40:02

Sudak_2008

Member Since: September 2008 Contribution: 2

RE: What is AMP parameter and its use e.g. AMP='BUFNI=10,BUFND=10' means what?

Could you please tell why this AMP parameter is not always mandatory whenever we access a VSAM file? Because I sometimes see it is used with some VSAM files and sometimes not.

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February 18, 2009 08:36:52

memays

Member Since: November 2007 Contribution: 5

RE: What is AMP parameter and its use e.g. AMP='BUFNI=10,BUFND=10' means what?

The AMP parameter is only used for VSAM files and mainly affects performance.

When VSAM files are defined via the DEFINE CLUSTER statement using IDCAMS certain parameters describe the physical format of the file while others define default performance charateristics of the file depending on how it will be most often used (e.g. Sequentially read Randomly Read Update and Delete activity etc.).

The AMP (Access Method Parameters) option allows these performance options to be overridden at runtime in the event that the file is going to be processed in a different manner than normal.

In the case of BUFNI(Index Buffers) and BUFND(Data Buffers) these parameters affect the amount of buffer space reserved for frequently used data in memory to avoid the repeated I/O's to reread data that has already been read. These buffers can greatly aid performance when a file is read sequentially using a concept known as "Anticipated Read" which causes not only the requested record to be read but also the "anticipated" next records in the file. When the next record is requested it is already in a buffer(memory) and the system does not need to perform an I/O to get it.

In an online(CICS) environment these parameters become very important as different CICS applications may process the same VSAM file in different manners.

If you are processing the file in the manner intended by whoever created the original definition then the AMP overrides should not be needed.

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