Re: Auto Tuning

Nathan,

It seems you have confused terms here.
Paging is not "a useless activity". If you need database records, they must
be paged into memory. How is that a useless activity?

You seem to have only part of the picture about performance and performance
tuning. In previous emails, you have said things like:
"Adjusting the time slice always makes somebody wait longer for their chance
to run."
and
"Auto tuning helps establish some overall equity between jobs of similar
classes."
and
"Manual tuning may be considered a black art because it creates the illusion
of better performance."
All of these are opinion only and indicate you are missing some things about
performance tuning. Over the last few weeks, following a performance
methodology, we have increased throughput and balanced workload with manual
tuning on several iSeries. None of the manual performance tuning has
degraded performance in any way, and the better performance has been
recorded, not magicked or illusioned.
The methodology we have followed has been:
1) Separate like jobs into their own subsystems and pools.
2) Monitor and adjust pool sizes and activity levels for optimum throughput.
3) Create several configurations for different workloads - daytime, evening,
weekend, monthend, etc..
4) Reduce timeslices across the board.
If there is an autotuner - it has been throttled by adjusting the maximum
and minimum thresholds.

Adjusting the timeslices down has meant that time spent on wasted timeslice
activity (yes, it happens) has been reduced and the system performs better.
Autotuning is not to make similar classes of jobs have equity, but ALL jobs
across the system be treated according to the prescribed authorities.

Not sure if this helps you any..
Trevor


----- Original Message ----- 
From: "Nathan M. Andelin"
Subject: Re: Auto Tuning


> Clare,
>
> It sounds like we agree that Peter is robbed to pay Paul when pool memory
> sizes and activity levels are adjusted, but whether auto tuning or manual
> tuning is doing the robbing, is a matter of perspective.
>
> The case for enabling auto tuning is that its primary function is to
> minimize paging.  When there's no paging, the auto tuner leaves memory and
> activity levels alone.  Paging is a useless activity that robs CPU time
from
> threads that perform meaningful work.  When paging is high, memory may be
> added, or the activity level reduced.  For the benefit of all, it makes
> sense to minimize paging.
>
> Although believable, it sounds pathetic that manual tuning is needed for
the
> benefit of SQL.  It sounds like application developers are abdicating
their
> responsibility for writing efficient code.  It's sad that the SQL
optimizer
> would need to be activated to soften a problem that should have been taken
> care of when the code was written.
>
> When adjusting time slice, keep in mind that depending on iSeries model,
the
> CPU on one system may be 20+ times faster than another (among current
> models), and CPU speed has increased from one generation of the box to the
> next.
>
> Nathan.