cpu usage of DB2 started tasks

william giannelli

cpu usage of DB2 started tasks

Normally, what is the cpu usage of the DB2 started tasks, highest to lowest? would the order go DBM1, DIST, MSTR then IRLM? Depending of course if you have distributed processing...........

thanks

Bill

Chris Hoelscher

cpu usage of DB2 started tasks
(in response to william giannelli)
Well – our busiest DOES have quite a bit of distributed
Memlimit excp cpu
DIST 16EB 4,781,850 7:51:20.00
W000 50GB 179,127K 44:32.92
MSTR 16EB 214,734K 10:03.33
DBM1 4TB 2,431M 05:11.93
IRLM 4GB 161 00:57.45
W000 50GB 8,412 00:06.00
W000 50GB 2,386 00:04.91
WDB0 50GB 149,526 00:03.29

Thank You,
Chris Hoelscher
Lead Database Administrator
IBM Global Technical Services
T 502.476.2538 or 502.407.7266

From: william giannelli <[login to unmask email]>
Sent: Friday, July 24, 2020 10:41 AM
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Subject: [DB2-L] - cpu usage of DB2 started tasks

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Normally, what is the cpu usage of the DB2 started tasks, highest to lowest? would the order go DBM1, DIST, MSTR then IRLM? Depending of course if you have distributed processing...........

thanks

Bill

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Michael Hannan

RE: cpu usage of DB2 started tasks
(in response to william giannelli)

William,

I think it depends greatly on your shop. Some sites do low DISTSERV processing, but in most, it should dominate.

IRLM is most important region for priority, because we want Locks to be real fast if granted. However it has far less total work to do. Thank god for Lock Avoidance. Lock CPU is sync processing capable of being charged back to the application. Not sure if that is true for an IRLM delegated to resolve a Data Sharing inter member contention.

DBRM1 does by far the most work encompassing Data Manager, Index Manager, Buffer Pool Manager, and even Relational  Data System Manager, and Native Stored Procs, but charges most of its processing back to the application or to DISTSERV. What remains is largely Dataset Open and Closes (TCB time), and Async Prefetch (SRB time) these days offloadable to zIIP processors.   So DBM1 can appear quite low. If its  GP CPU gets high, that is a worry, for possiblly Dataset Opens and Closes.

MSTR   looks after System Admin tasks, like Log Switch and Archive,  as just one example, and CPU will be for things that cannot be attributed back to application. 

So most DB2 regions appear to use far less CPU than the total work being done by DB2 or even by that region. That is why mostly we don't look closely at CPU in the IRLM, MSTR, and DBM1 regions, unless they have got quite significant.

Before offload to zIIP, one colleague used to say that he expected DBM1 SRB (Prefetch) to be about 10 times higher than TCB (Open and Closes) in normal systems. I would say, wogwash! The 2 measures have nothing to do with each other and the ratio is meaningless. Very high TCB, I would be concerned, but without any concern of its ratio to Prefetch work. Prefetch CPU could fluctuate widely depending on tuning of access paths to scan or to use better indexes.

So relativity of CPU between the regions could be somewhat limited in  meaning too.

Michael Hannan,
DB2 Application Performance Specialist

Edited By:
Michael Hannan[Organization Members] @ Jul 25, 2020 - 02:27 PM (Australia/Melbourne)
Michael Hannan[Organization Members] @ Jul 25, 2020 - 02:29 PM (Australia/Melbourne)