Re: Context switch storm

["Gregory S. Williamson" <gsw(at)globexplorer(dot)com>]

Based on what other people have posted, hyperthreading seems not to be beneficial for postgres -- try searching through the archives of this list. (And then turn it off and see if it helps.)

You might also post a few details:

config settings (shared_buffers, work_mem, maintenance_work_mem, wal and checkpoint settings, etc.)

are you using autovacuum ?

all tables are vacuumed and analyzed regularly ? How big are they ? Do they and indexes fit in RAM ?

any particular queries that running and might be related (explain analyze results of them would be useful)

disk configuration

Other processes on this box ?

# of connections to it (I've seen this alone push servers over the edge)

HTH,

Greg Williamson
DBA
GlobeXplorer LLC

-----Original Message-----
From:	pgsql-performance-owner(at)postgresql(dot)org on behalf of creimer(at)brturbo(dot)com(dot)br
Sent:	Fri 11/3/2006 2:32 AM
To:	pgsql-performance(at)postgresql(dot)org
Cc:	
Subject:	[PERFORM] Context switch storm

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 is producing this context switching storms?
 
It is a box with 16GB RAM and 4 XEON processors running RedHat Enterprise Linux AS.
 
Should I disable Hyperthreading?
 
Thank you in advance!
 
Reimer



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