Re: PATCH: Split stats file per database WAS: autovacuum stress-testing our system

Tomas Vondra escribió:

> On 14.2.2013 20:23, Alvaro Herrera wrote:

> > The problem here is that creating these dummy entries will cause a
> > difference in autovacuum behavior. Autovacuum will skip processing
> > databases with no pgstat entry, and the intended reason is that if
> > there's no pgstat entry it's because the database doesn't have enough
> > activity. Now perhaps we want to change that, but it should be an
> > explicit decision taken after discussion and thought, not side effect
> > from an unrelated patch.
>
> I don't see how that changes the autovacuum behavior. Can you explain
> that a bit more?
>
> As I see it, with the old (single-file version) the autovacuum worker
> would get exacly the same thing, i.e. no stats at all.

See in autovacuum.c the calls to pgstat_fetch_stat_dbentry(). Most of
them check for NULL result and act differently depending on that.
Returning a valid (not NULL) entry full of zeroes is not the same.
I didn't actually try to reproduce a problem.

--
Álvaro Herrera http://www.2ndQuadrant.com/
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