Mainframe, MVS and zOS Discussion

Hi,

What is the best way to choose the control interval size for the data and index in VSAM? And should we even bother about it while defining a VSAM?

As of now I look at the existing VSAM, used for similar work and define the new VSAM file.

The access pattern should help determine CI sizes. For a KSDS being read completely randomly, use a shorter data CI size; for a completely sequential access, use a longer data CI size. How long or how short? That depends on a lot of factors -- average record length, free space needed, etc. For the index CI size, the one thing you want to make sure of is that the CI size is big enough to allow access to all the data CI -- if not, you're wasting space.