Re: Shared memory usage

On Sun, 26 Aug 2007 00:39:52 +0400, Martijn van Oosterhout
<kleptog@svana.org> wrote:

> 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,

Could it be that most of the cpu usage is from lots of fast indexed sql
queries
wrapped in sql functions?