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Re: Need suggestions on kernel settings for dedicated FreeBSD/Postgresql machine

From: Ivan Voras <ivoras(at)freebsd(dot)org>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: Need suggestions on kernel settings for dedicated FreeBSD/Postgresql machine
Date: 2009-08-18 14:12:17
Message-ID: h6ecs1$qls$1@ger.gmane.org (view raw or flat)
Thread:
Lists: pgsql-performance
Culley Harrelson wrote:
> I will definitely look into this.  I suspect I need to tune my kernel
> settings first though...

No, not much. Sysctl and loader.conf settings are enough.

>>> $ cat /etc/sysctl.conf
>>>
>>> kern.ipc.shmmax=268435456
>>> kern.ipc.shmall=65536

shmmax is in bytes, so this is 256 MB - way too low.
shmall is in pages, so this is 256 MB also - which is in sync with the 
above but will fall apart if some other service needs shm memory.

Set shmall to 2 GB and shmmax to 1.9 GB.

>>> $ cat /boot/loader.conf
>>> kern.ipc.semmni="256"
>>> kern.ipc.semmns="512"
>>> kern.ipc.semmnu="256"

I think these are way too low also. I use 10240 and 16384 for semmni and 
semmns habitually but these might be overtuned :)

>>> In postgresql.conf I have:
>>>
>>> max_connections = 180
>>> shared_buffers = 28MB

Definitely too low and out of sync with the above settings.

Set shared_buffers to around 1800 MB or 1900 MB.

These settings are a good start, but you can find many tutorials and 
documents on tuning pgsql if you search around.


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