Re: Never-idle autovacuum, and does (auto)vacuuming fill the OS cache ?

On Thu, Oct 06, 2011 at 11:58:15AM +0200, Vincent de Phily wrote:
> Fearing that vacuuming might accumulate lateness and hoping to see the system
> idle every now and then,

Why is your goal to see the system idle every now and then? It's not
going to get tired if it keeps working, and if you have a lot of work
and can spin out that work so that the system always has a little bit
of work to do, then you use your resources more efficiently.

Normally, one likes to see some idle time because it is evidence of
"headroom" -- that you have more capacity than you actually need. If
that's the reason you want to see the idle times, then surely you
don't want to tune the system with the goal of causing idleness. You
want to tune the system so that the work gets done in as smooth and
fast a way possible. So I would aim for maximum throughput (including
but not exclusively complete table maintenance) and then check whether
you're getting any idle time. Off the cuff, though, it sounds to me
like you need more capacity than you have.

> This is all on PG 8.3. I know upgrading would improve things
> (particularly since a large percentage of the table remains static
> between vacuums), but we're still too busy for that right now
> (unless you tell me I'm going to see a night-and-day difference
> regarding this particular issue).

I think it might be more "dusk and day", but I have had very
impressive performance from 9.0. Haven't tried 9.1.

A

--
Andrew Sullivan
ajs(at)crankycanuck(dot)ca