Subject: Re: High CPU Load
From: =?ISO-8859-1?Q?J=E9r=F4me?= BENOIS <benois@argia-engineering.fr>
To: Markus Schaber <schabi@logix-tt.com>
Cc: pgsql-performance@postgresql.org
In-Reply-To: <450A75DE.6050102@logix-tt.com>
References: <1158239339.5226.17.camel@localhost.localdomain>
	<450A75DE.6050102@logix-tt.com>
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Date: Mon, 18 Sep 2006 16:44:05 +0200
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Hi Markus,

Le vendredi 15 septembre 2006 =C3=A0 11:43 +0200, Markus Schaber a =C3=A9cr=
it :
> Hi, J=C3=A9r=C3=B4me,
>=20
> J=C3=A9r=C3=B4me BENOIS wrote:
>=20
> > max_connections =3D 512
>=20
> Do you really have that much concurrent connections? Then you should
> think about getting a larger machine, probably.
>=20
> You will definitely want to play with commit_delay and commit_siblings
> settings in that case, especially if you have write access.
>=20
> > work_mem =3D 65536
> > effective_cache_size =3D 131072
>=20
> hmm, 131072*8*1024 + 512*65536*1024 =3D 35433480192 - thats 33 Gig of
> Memory you assume here, not counting OS usage, and the fact that certain
> queries can use up a multiple of work_mem.

Now i Have 335 concurrent connections, i decreased work_mem parameter to
32768 and disabled Hyper Threading in BIOS. But my CPU load is still
very important.

Tomorrow morning i plan to add 2Giga RAM ... But I don't understand why
my database server worked good with previous version of postgres and
same queries ...

> Even on amachine that big, I'd be inclined to dedicate more memory to
> caching, and less to the backends, unless specific needs dictate it. You
> could try to use sqlrelay or pgpool to cut down the number of backends
> you need.
I used already database pool on my application and when i decrease
number of connection my application is more slow ;-(
>=20
> > My Server is Dual Xeon 3.06GHz
>=20
> For xeons, there were rumours about "context switch storms" which kill
> performance.
I disabled Hyper Threading.
> > with 2 Go RAM and good SCSI disks.
>=20
> For 2 Gigs of ram, you should cut down the number of concurrent backends.
>=20
> Does your machine go into swap?
No, 0 swap found and i cannot found pgsql_tmp files in $PG_DATA/base/...
>=20
> Markus
--=20
J=C3=A9r=C3=B4me,

python -c "print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in 'sioneb@gnireenigne-aigra.rf'.split('@')])"

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