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Message Posted: Wed, 06 Sep 2001 @ 21:15:48 GMT
Regarding policies, the really don't "allocate resources". The policies help determine how the weight of a process is calculated, which leads to determining it's overall priority. The IMD/DEF policies seem to work very similarly. I haven't seen a significant difference in the two, in my experience. I know that in V2R3, there were some PSF problems that were eliviated when using IMM vs. DEF, but I believe those have been corrected in later versions of the DBMS. (PTDBMS .101 I think, but don't quote me.) IMM is supposed to provide a little better service to very short queries in a mixed workload.
REL is different in that it, potentially, caps the amount of resources that can be consumed to a certain percentage. This can be pretty powerful in ensuring that certain workloads are guaranteed some amount of the system. For example, if there are two workloads, workload A with a DEF policy and a weight of 70 and the workload B with a REL policy and a weight of 30, as long as workload A has active sessions on the system, workload B will not consume more than 30% of the total resources. Therefore, even if workload B is using it's full 30% and could use more, if workload A is doing work, workload B will be limited. If workload A is not active, workload B could use up to 100% of all resources on the system. This is why the REL policy could result in system idle time. The ABS policy can also cause idle time.
Regarding active status, PSF keeps a track of CPU used for a performance group and partition over a 60 second interval (default setting). If no CPU activity for the performance group or partition is record over that period of time, the performance group or partition is considered inactive and is no longer a factor in calculating future weightings until the group becomes active again. It does not matter whether the sessions are logged on or not.
SHAMELESS PLUG TO FOLLOW
Steve Thill of Sears and I will be presenting our real life experiences with Priority Scheduler at Partners in October. It's a follow on to the PSF article in the latest version of Teradata magazine.
Thomas F. Stanek
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