Re: 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
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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