CICS VSAM Buffering
MartinPacker 11000094DH Comments (5) Visits (19429)
Four score and seven years ago (or so it seems) the Washington Systems Center published a set of mainframe Data-In-Memory studies. These were conducted by performance teams in various IBM labs and were quite instructive and inspiring. I wish I could find the form number (and a fortiori a PDF version) for this book. Anyone? Even hardcopy would be really nice.
The reason I mention this is because of a thread in the CICS-L newsgroup overnight about the CPU impact of increasing the size of VSAM LSR buffers in CICS. I seem to recall that CICS / VSAM was one of the benchmarks written up in this orange book. The original poster wanted to know what the CPU impact profile was of increasing VSAM buffers. I think the study showed that there could be some CPU saving with bigger buffer pools. (Compare this with VIO in (then) expanded storage - which showed a net CPU increase for the technique.)
There are a number of points I would have raised in CICS-L but I'll write them here instead - as most of you probably don't read CICS-L:
In general I find CICS VSAM LSR buffering insufficiently aggressive: As memory is generally plentiful these days (at least relative to the CICS VSAM LSR pool sizes I encounter) I think it's appropriate for installations to consider big increases (subject to the provisoes above). Think in terms of doubling rather than adding 20%. And no 10MB total buffering is not aggressive.