Re: Why shared_buffers max is 8GB?

I wanted to follow up from this question. I’m running on 9.3.4
My DB server has 32GB ram so I have assigned 8GB shared_buffer_memory. It is quite a big db but with not much traffic. When there is traffic, it’s usually big.

Lately, the kernel has been killing the postmaster for having assigned too much shared memory. Latest crash was when loading a 500MB file.

Should I reduce the shared buffers in order for this to be more robust?

Thanks
Markella

From: desmodemone
Sent: Wednesday, March 26, 2014 12:45 PM
To: ik(at)postgresql-consulting(dot)com
Cc: pgsql-performance(at)postgresql(dot)org ; Alexey Vasiliev
Subject: Re: [PERFORM] Why shared_buffers max is 8GB?

Il 26/mar/2014 13:36 "Ilya Kosmodemiansky" <ilya(dot)kosmodemiansky(at)postgresql-consulting(dot)com> ha scritto:
>
> Hi Alexey,
>
> On Wed, Mar 26, 2014 at 1:21 PM, Alexey Vasiliev <leopard_ne(at)inbox(dot)ru> wrote:
> > I read from several sources, what maximum shared_buffers is 8GB.
>
> I believe that was an issue on some older versions, and thats why was
> mentioned in several talks. Today it is a sort of apocrypha.
>
> > Does this true? If yes, why exactly this number is maximum number of
> > shared_buffers for good performance (on Linux 64-bits)?
>
> 25% of available RAM is a good idea to start. Sometimes, if you have
> heavy workload _and_ it is possible to reside whole database in
> memory, better to use something larger, about ~75% of RAM.
>
> Best regards,
> Ilya
> --
> Ilya Kosmodemiansky,
>
> PostgreSQL-Consulting.com
> tel. +14084142500
> cell. +4915144336040
> ik(at)postgresql-consulting(dot)com
>
>
> --
> Sent via pgsql-performance mailing list (pgsql-performance(at)postgresql(dot)org)
> To make changes to your subscription:
> http://www.postgresql.org/mailpref/pgsql-performance

max is 1024mb.

you have to test your workload if it's too low you will get too much i/o ( the filesystem cache could help.. not always /*nfs*/), if too high your cpu will be eated by lru/ latch/ and so on.

Mat Dba