Establishing VSAM Data and Index Buffers

How to:

Two SET commands make it possible to establish DATA and INDEX buffers for processing VSAM data sources online.

The AMP sub-parameters BUFND and BUFNI enable users to enhance the I/O efficiency of TABLE, TABLEF, MODIFY, and JOIN against VSAM data sources by holding frequently used VSAM Control Intervals in memory, rather than on physical DASD. By reducing the number of physical Input/Output operations, you may improve job throughput. In general, BUFND (data buffers) increase the efficiency of physical sequential reads, whereas BUFNI (index buffers) are most beneficial in JOIN or KEYED access operations.
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Syntax: How to Establish VSAM Data and Index Buffers
ENGINE VSAM SET BUFND {n|8}
ENGINE VSAM SET BUFNI {n|1}

where:

n

Is the number of data or index buffers. BUFND=8 and BUFNI=1 (eight data buffers and one index buffer) are the default values. The AMODE parameter determines whether the buffers are created above or below the line. SET AMODE=31 places the buffers above the line. SET AMODE=24 places the buffers below the line.

To determine how many buffers are in effect at any time, issue the query:

ENGINE VSAM SET ?
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