(Originally posted 2006-11-30.)
In z/OS Release 8 Real Storage Manager (RSM) implemented brand new algorithms. One of the more significant changes was the adoption of a “new style” UIC value. This behaves much more like the old Expanded Storage Migration Age. Accordingly the old UIC value (SMF71ACA) isn’t really appropriate to use anymore. Or at least it won’t behave the way it used to.
And before I go any further the SMF Type 71 record is the one that accompanies the RMF “Paging Activity” report. But most people process it into a database and graph its fields from there.
Now, the point of this blog entry is to alert readers who like to look at low-level SMF records that the Paging Data section in SMF 71 has been extended from 1040 bytes (ending at SMF71AFB) to 1120 bytes. The new fields can be summarised as:
- Information on shared pages, typically in 8-byte floating point fields.
- New numbers on UIC values, as 4-byte integers.
It’s the latter I want to focus on…
There are a whole host of these UIC fields, giving much more detail on how UIC varies through time. When the documentation refers to “Average current system UIC during the interval” (SMF71UAC), for example, it’s important to bear in mind that the interval consists of some number of samples. So the “Average” refers to averaging across the samples, and the “current” refers to the value at the end of one of the sample periods. It’s rather confusing terminology – but that’s the nature of the beast.
I expect, in a subsequent blog entry, to talk more about the new RSM algorithms themselves.