Secondary extents allocation for Insight History files.

Products

• SYSVIEW Performance Management Option for DB2 for z/OS

Issue/Introduction

In the HIGHLVL.SOURCE (SSIDVSAM) the comments for  HSTSTATS and HSTACCTG allocation states Secondary extents must not be specified. What is the reason for that?

 

 

Environment

Release:
Component: IDB2

Resolution

You can specify a secondary allocation, but that will cause VSAM to continue to extend the data set until the maximum number of extents are reached (125 for non-extended VSAM) or the volume fills up. It won't wrapp the data until that happens. With no secondary space defined, the wrapping of data occurs as soon as the primary extent is filled. That is far more preferable in terms of both performance and space management.