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Re: postgres bogged down beyond tolerance

From: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
To: Tena Sakai <tsakai(at)gallo(dot)ucsf(dot)edu>
Cc: pgsql-admin(at)postgresql(dot)org
Subject: Re: postgres bogged down beyond tolerance
Date: 2007-11-14 19:08:14
Message-ID: 20071114190814.GU19014@alvh.no-ip.org (view raw or flat)
Thread:
Lists: pgsql-admin
Tena Sakai wrote:

> I checked kernel parameter
> shmmax and it was set as 33554432.  I "fixed" it as
> suggested by the manual:
> http://www.postgresql.org/docs/8.2/static/kernel-resources.html

Note that just by changing shmmax you're not doing anything to Postgres
itself.  If you want Postgres to use more memory, you need to increase
shared_buffers in postgresql.conf.  Changing shmmax is only required so
that the kernel allows Postgres to allocate all those shared_buffers.

> Namely, I shutdown the database, issued two commands:
>   /sbin/sysctl -w kernel.shmmax=134217728
>   /sbin/sysctl -w kernel.shmall=2097152
> and rebooted the computer.
> 
> After it came up, I checked the shmmax and it is set
> as 33554432.  Which surprised me.  Since I used -w
> flag, I thought it should've written to /etc/sysctl.conf,
> but there is no such entry at all and the data of this
> file is from 2006.

No, the -w actually means "write to the kernel", which is state that
doesn't persist by itself.  It's your own responsability to write it to
sysctl.conf.

Anyhow, I don't think any of this has anything to do with a performance
problem.  If you haven't ever vacuumed your database, do so now and try
again.  (Actually, have a read of the "maintenance" chapter in the
manual).

-- 
Alvaro Herrera       Valdivia, Chile   ICBM: S 39º 49' 18.1", W 73º 13' 56.4"
Voy a acabar con todos los humanos / con los humanos yo acabaré
voy a acabar con todos / con todos los humanos acabaré (Bender)

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