Hello Buck,
Buck <
kc2...@gmail.com> wrote:
> And I assure you that any advice you found to tune an AS400 does not apply to
> IBM i. It's not just a new paint job - the work management has been very much
> rewritten in the 20 years since AS400 was made.
In strongly disagree. While IBM did substantial changes under the the hood, the
basic principles still apply:
- Paging platform, paging globally, and not per application. RAM = Cache.
- Confine paging to subsystems/memory pools to adjust relative performance of
jobs against each other competing for common resources.
- Adjust activity levels to prevent thrashing and keep DASD latency low. Most
often, DASD is shared globally so this easily becomes a major bottleneck.
What *has* changed from a sysadmin point of view is that RAM and CPU cycles are
available in abundance for years now and production machines are rarely that
severely memory constrained as they were in 1990. My personal experience
over 15 years working with the system showed that most often, it's perfectly
sufficient to just enable dynamic resource adjustments at run time only by
setting QPFRADJ to 3, and enable expert cache with PAGING(*CALC). And let the
system decide for itself where resources are needed and what do to about it.
> I've been tuning IBM systems, applications, and programs for 30+ years. If
> you want to get into this area, read the Work Management manual, then read it
> again. That second reading will make more sense after you have seen all of
> the subjects once.
I agree. Also there are some books on the subject, I'd recommend:
- Chuck Stupca - iSeries and AS400 Work Management
- Fielder, Machell - Supercharging the AS400, A Guide to Performance Management
- Michael Catalani - AS400 Performance Tuning Simplified
These not only show what's important for memory constrained AS/400's, but the
authors manage to explain the mysteries behind subsystems, and memory pools.
Concepts not known from common systems. Yes, they are rather dated but as
explained above, the same principles still apply. Although not to the extent
shown, because of much much more memory nowadays.
> Learn how to run Performance Explorer to gather
> So:
> 1) Don't guess. Measure!
> 2) Don't try random things. Understand what each thing does.
A very important advice!
:wq! PoC