A CF cache structure must be at least large enough to hold all of the MVS information required to describe a structure of maximum size. To help you achieve the best possible performance with VSAM RLS buffering, the sum total of all the CF cache structure sizes you define (the CF cache) should ideally be the sum total of the local VSAM local shared resources (LSR) buffer pool sizes. The size of the local VSAM LSR buffer pool is the sum of LSR pool size and, if used, the corresponding Hiperspace™ pool size. You can run VSAM RLS with less CF cache storage than this, but the CF cache must be large enough for the CF cache directories to contain an entry for each of the VSAM RLS local buffers across all instances of the SMSVSAM server. If the CF cache cannot contain the directory entries describing the local buffers, then the VSAM RLS local buffers are falsely invalidated and must be refreshed. To minimize this, the minimum CF cache structure size should never be less than 1/10 the size of the local buffer pool.

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

In those situations where you can determine that data previously treated as a nonshared resource (NSR) is no longer to be treated as such, you should also include NSR buffer sizes in the total local buffer pool size.