Re: Shared memory usage

On Sun, Aug 26, 2007 at 01:22:58AM +0400, Max Zorloff wrote:
> Hello.
>
> I have a postgres 8.0 and ~400mb database with lots of simple selects
> using indexes.
> I've installed pgpool on the system. I've set num_init_children to 5 and
> here is the top output.
> One of postmasters is my demon running some insert/update tasks. I see
> that they all use cpu heavily, but do not use the shared memory.
> shared_buffers is set to 60000, yet they use a minimal part of that. I'd
> like to know why won't they use more? All the indexes and half of the
> database should be in the shared memory, is it not? Or am I completely
> missing what are the shared_buffers for? If so, then how do I put my
> indexes and at least a part of the data into memory?

shared_memory is used for caching. It is filled as stuff is used. If
you're not using all of it that means it isn't needed. Remember, it is
not the only cache. Since your database is only 400MB it will fit
entirely inside the OS disk cache, so you really don't need much shared
memory at all.

Loading stuff into memory for the hell of it is a waste, let the system
manage the memory itself, if it needs it, it'll use it.

Have a nice day,
--
Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> From each according to his ability. To each according to his ability to litigate.