Using data tables to improve performance

Data tables enable you to build, maintain and have rapid access to data records contained in tables held in virtual storage above the 16MB line. Therefore, they can provide a substantial performance benefit by reducing DASD I/O and pathlength resources. The pathlength to retrieve a record from a data table is significantly shorter than that to retrieve a record already in a VSAM buffer.

Effects

For CICS-maintained data tables, CICS ensures the synchronization of source data set and data table changes. When a file is recoverable, the necessary synchronization is already effected by the existing record locking. When the file is nonrecoverable, there is no CICS record locking and the note string position (NSP) mechanism is used instead for all update requests. This may have a small performance impact of additional VSAM ENDREQ requests in some instances.

Recommendations

How implemented

Data tables can be defined using either the DEFINE FILE command of the CEDx transaction or the DFHCSDUP utility program. See the CICS Resource Definition Guide for more information.

How monitored

Performance statistics are gathered to assess the effectiveness of the data table. They are in addition to those available through the standard CICS file statistics.

The following information is recorded:

There are circumstances in which apparent discrepancies in the statistics may be seen, caused, for example, by the existence of inflight updates.

Related tasks
VSAM and file control: improving performance
VSAM tuning: general objectives
Defining VSAM buffer allocations for NSR (INDEXBUFFERS and DATABUFFERS)
Defining VSAM buffer allocations for LSR
Defining VSAM string settings for NSR (STRINGS)
Defining VSAM string settings for LSR (STRINGS)
Specifying maximum keylength for LSR (KEYLENGTH and MAXKEYLENGTH)
Specifying resource percentile for LSR (SHARELIMIT)
Using VSAM local shared resources (LSR)
Using Hiperspace buffers
Permitting VSAM subtasking (SUBTSKS=1)
Using coupling facility data tables to gain performance benefits
Performance aspects of VSAM record-level sharing (RLS)
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