Re: optimal memory

In response to Sim Zacks :
>
>
> On 03-Aug-2010 11:18 AM, A. Kretschmer wrote:
> > In response to Sim Zacks :
> >
> >> Is there a way to tell what the optimal memory is for a specific
> >> postgresql instance?
> >>
> >> I am configuring Xen virtual machines and I don't want to give it more
> >> then it needs.
> >>
> >> Would looking at the swap be an indication? As soon as it starts to use
> >> swap, that means I need more, but until that point, I have enough?
> >>
> > You can't have enough ;-)
> >
> > Fits your DB into the RAM?
> >
> > If you don't have enough, for instance, work_mem, sort-operations
> > performed on disk and not in the ram. That's much slower. So, as i said,
> > you can't have enough ram ;-)
> >
> In theory that's a great answer.

;-)

> If my database is 400MB (du on the base directory) and there are 10
> active users running functions and queries, that for the most part take
> less then 1 sec each.
> I would assume that 10GB of RAM is overkill.

Maybe.

> Is 2 GB RAM also overkill? Is there a way to know when you have reached
> the overkill level?

I think, you should try it. Set your virtual machine to 2 GByte, set
shared_buffers to 512 MByte, effective_cache_size to 1.5 gbyte and
work_mem to, for instance, 20 mbyte. Monitor the machine, watch the
logfile (set log_min_duration_statement properly).

Reduce all parameters to 50% and compare the results.

Andreas
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Andreas Kretschmer
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