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* Context switching
@ 2006-11-01 05:23 Carlos H. Reimer <carlos.reimer@opendb.com.br>
0 siblings, 1 reply; 2+ messages in thread
From: Carlos H. Reimer @ 2006-11-01 05:23 UTC (permalink / raw)
To: pgsql-performance
Hi,
We've migrated one of our servers from pg 7.4 to 8.1 and from times to times
(4 hours) the server start doing a lot of context switching and all
transactions become very slow.
The average context switching for this server as vmstat shows is 1 but when
the problem occurs it goes to 250000.
CPU and memory usage are ok.
What can produce this context switching storms?
It is a box with 12GB RAM and 4 processors running RedHat Enterprise Linux
AS.
Thank you in advance!
Reimer
carlos.reimer@opendb.com.br
OpenDB Serviços e Treinamentos PostgreSQL e DB2
Fone: 47 3327-0878 Cel: 47 9602-0151
www.opendb.com.br
^ permalink raw reply [nested|flat] 2+ messages in thread
* Re: Context switching
@ 2006-11-07 17:42 Josh Berkus <josh@agliodbs.com>
parent: Carlos H. Reimer <carlos.reimer@opendb.com.br>
0 siblings, 0 replies; 2+ messages in thread
From: Josh Berkus @ 2006-11-07 17:42 UTC (permalink / raw)
To: pgsql-performance; carlos.reimer@opendb.com.br
Carlos,
> We've migrated one of our servers from pg 7.4 to 8.1 and from times to
> times (4 hours) the server start doing a lot of context switching and all
> transactions become very slow.
>
> The average context switching for this server as vmstat shows is 1 but when
> the problem occurs it goes to 250000.
Context Switching is a symptom rather than a cause. What's most likely
happening is that you have a combined heavy-CPU and heavy-IO workload, so you
have bursts of CPU activity stalled by iowaits.
Can you check the rate of iowaits during the "storm" periods?
Also, is this Xeon? And are you saying that you *didn't* have this issue
under 7.4?
--
Josh Berkus
PostgreSQL @ Sun
San Francisco
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2006-11-01 05:23 Context switching Carlos H. Reimer <carlos.reimer@opendb.com.br>
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