Re: Memory limits and PostgreSQL 8.4 - Over 63 GB of memory for DB?

> -----Original Message-----
> From: pgsql-admin-owner(at)postgresql(dot)org [mailto:pgsql-admin-
> owner(at)postgresql(dot)org] On Behalf Of Tapio Pitkäranta
> Sent: Friday, March 18, 2011 4:10 AM
> To: Devrim GÜNDÜZ
> Cc: pgsql-admin(at)postgresql(dot)org
> Subject: Re: [ADMIN] Memory limits and PostgreSQL 8.4 - Over 63 GB of
> memory for DB?
>
> Hello,
>
> Thank you for the reply. It seems you might be right:
>
> /etc/sysctl.conf
>
> # Controls the maximum shared segment size, in bytes
> kernel.shmmax = 68719476736
>
> # Controls the maximum number of shared memory segments, in pages
> kernel.shmall = 4294967296
>
> We have tried to set shared_buffers over 63 GB.
>
> Do you have any advice on memory settings for servers with large
> amounts of memory (100-200GB)? It seems there is not too much
> documentation on that in the net.

This is unlikely to work out as you expect. Values for shared buffers over the 8-10GB range aren't recommended. It may need to be much lower, depending on your workload.

As far as recommendations - try and gauge the size of your working data set and size the shared buffers for that. From there - test with your workload, and watch out for checkpoint spikes.

Unused memory will still be available to the filesystem to cache data there.

Brad.