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The techniques used by NCL should ensure efficient processing of VSAM files. Additional performance gains can be obtained by the allocation of additional buffers and processing strings. This is achieved using the JCL AMP statement sub parameters on the DD statement for the file or options on the UDBCTL command:
The number of index buffers to be allocated by VSAM
The number of data buffers to be allocated by VSAM
The maximum number of concurrent strings VSAM is to use
By default, your product allocates 2 data buffers, 3 index buffers and 2 processing strings unless alternative values are provided as described.
This buffer allocation applies per string-that is, allocation of a complete set of buffers is performed by VSAM for each concurrent position held on the UDB. Where the usage of a UDB is such that a large number of concurrent accesses to the UDB might be possible, care must be taken that VSAM buffer allocations do not lead to storage shortages affecting the performance of other product functions. Also, in cases such as these, NCL procedures should be written to avoid the maintenance of generic UDB processing environments over long periods.
While varying these parameters can offer significant performance benefits, they should only be changed if the impact on VSAM processing is clearly understood. Incorrect changes can impose severe storage overheads which could impact the operation of other system components.
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