| From: | Robert Creager <Robert_Creager(at)LogicalChaos(dot)org> |
|---|---|
| To: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
| Cc: | pg(at)fastcrypt(dot)com, Josh Berkus <josh(at)agliodbs(dot)com>, Dirk_Lutzebäck <lutzeb(at)aeccom(dot)com>, ohp(at)pyrenet(dot)fr, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Joe Conway <mail(at)joeconway(dot)com>, "scott(dot)marlowe" <scott(dot)marlowe(at)ihs(dot)com>, pgsql-performance(at)postgresql(dot)org, Neil Conway <neilc(at)samurai(dot)com> |
| Subject: | Re: Wierd context-switching issue on Xeon |
| Date: | 2004-05-20 01:59:26 |
| Message-ID: | 20040519195926.3c5fa3bc@thunder.mshome.net |
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| Lists: | pgsql-performance |
When grilled further on (Wed, 19 May 2004 21:20:20 -0400 (EDT)),
Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> confessed:
>
> Did we ever come to a conclusion about excessive SMP context switching
> under load?
>
I just figured out what was causing the problem on my system Monday. I'm using
the pg_autovacuum daemon, and it was not vacuuming my db. I've no idea why and
didn't get a chance to investigate.
This lack of vacuuming was causing a huge number of context switches and query
delays. the queries that normally take .1 seconds were taking 11 seconds, and
the context switches were averaging 160k/s, peaking at 190k/s
Unfortunately, I was under pressure to fix the db at the time so I didn't get a
chance to play with the patch.
I restarted the vacuum daemon, and will keep an eye on it to see if it behaves.
If the problem re-occurs, is it worth while to attempt the different patch
delay settings?
Cheers,
Rob
--
19:45:40 up 21 days, 2:30, 4 users, load average: 2.03, 2.09, 2.06
Linux 2.6.5-01 #7 SMP Fri Apr 16 22:45:31 MDT 2004
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