Running efficiently with CICS, IMS, or VSAM

You can improve performance for online programs running under CICS® or IMS, or programs that use VSAM, by following these tips.

CICS: If your application runs under CICS, convert EXEC CICS LINK commands to COBOL CALL statements to improve transaction response time.

IMS: If your application runs under IMS, preloading the application program and the library routines can help reduce the overhead of loading and searching. It can also reduce the input-output activity.

For better system performance, use the RENT compiler option and preload the applications and library routines when possible. You can also use the Language Environment® library routine retention (LRR) function to improve performance in IMS/TM regions.

VSAM: When you use VSAM files, increase the number of data buffers for sequential access or index buffers for random access. Also, select a control interval size (CISZ) that is appropriate for the application. A smaller CISZ results in faster retrieval for random processing at the expense of inserts. A larger CISZ is more efficient for sequential processing.

For better performance, access the records sequentially and avoid using multiple alternate indexes when possible. If you use alternate indexes, access method services builds them more efficiently than the AIXBLD runtime option.

related references  
Language Environment Programming Guide (Specifying runtime options)