You need to define cache structures large enough for the activity of VSAM RLS as well as the additional activity of batch jobs that use DFSMStvs.

For the best performance with VSAM RLS buffering without DFSMStvs, the total of all of the coupling-facility cache-structure sizes that you define (the coupling-facility cache) should be the total of the VSAM local-shared-resource (LSR) buffer-pool sizes used in non-RLS mode. The VSAM LSR buffer-pool size is the sum of the LSR pool size and if used, the corresponding Hiperspace™ pool size.

You can run VSAM RLS with less coupling-facility cache storage than this, but the coupling-facility cache must be large enough for the coupling-facility cache directories to contain an entry for each of the VSAM RLS local buffers across all instances of the RLS server. Otherwise, the VSAM RLS local buffers become falsely not valid and must be refreshed. To minimize false invalidation, the size of the coupling-facility cache structure should be at least one-tenth of the sum of the local buffer-pool sizes.

Performance should improve when the coupling-facility cache is larger than the sum of the local VSAM LSR buffer pool sizes. When the coupling-facility cache is smaller, performance depends on the dynamics of the data references among the systems involved. In some cases, you might want to consider increasing the size of a very small (2 MB to 10 MB) coupling-facility cache.

Related reading: For more information about CICS® TS structures, see http://publib.boulder.ibm.com/infocenter/cicsts/v3r1/index.jsp .