Defining VSAM string settings for NSR (STRINGS)

STRINGS is used to determine the number of concurrent operations possible against the file and against the VSAM base cluster to which the file relates.

Effects

The STRINGS parameter for files using NSR has the following effects:

Strings represent a significant part of the virtual storage requirement of most CICS® systems. With CICS, this storage is above the 16MB line.

Where useful

The STRINGS parameter should be used in CICS systems that use VSAM NSR files in CICS file control.

Limitations

A maximum of 255 strings can be used as the STRNO or BSTRNO in the ACB.

Recommendations

See Number of strings considerations for ESDS files and VSAM tuning: general objectives.

How implemented

The number of strings is defined by the STRINGS parameter in the CICS file definition on the CSD. It corresponds to the VSAM parameter in the ACB except where a base file is opened as the first for a VSAM data set; in this case, the CICS-accumulated BSTRNO value is used as the STRNO for the ACB.

How monitored

The effects of the STRINGS parameter can be seen in increased response times and monitored by the string queueing statistics for each file definition. RMF™ can show I/O contention in the DASD subsystem.

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 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 data tables to improve performance
Using coupling facility data tables to gain performance benefits
Performance aspects of VSAM record-level sharing (RLS)
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