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Re: BUG #3898: Postgres autovacuum not respectingpg_autovacuum.enabled = false

From: Simon Riggs <simon(at)2ndquadrant(dot)com>
To: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Steven Flatt <steven(dot)flatt(at)gmail(dot)com>, pgsql-bugs(at)postgresql(dot)org
Subject: Re: BUG #3898: Postgres autovacuum not respectingpg_autovacuum.enabled = false
Date: 2008-01-24 09:19:17
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Lists: pgsql-bugs
On Thu, 2008-01-24 at 00:01 -0300, Alvaro Herrera wrote:

> IMO it's a usability bug which will be gone when we move to
> pg_class.reloptions -- you won't need to set random values for options
> you don't know what to set to.

But this is a problem in *this* release (and the last also?).

> As for documentation, this is mentioned somewhere.  Perhaps not clearly
> enough?   OTOH I think the real problem is that people think
> documentation can be skipped, thus they don't know the "fine print" --
> so it won't matter how non-fine we make it.

Not clear enough. I don't think Tom's suggested wording goes far enough
because not everybody understands this sufficiently to make the leap
that low settings will put you into a cycle of constant vacuuming.

We clamp autovacuum_freeze_max_age and autovacuum_freeze_min_age to
certain values, so I think we should do the same for values in the
pg_autovacuum table. i.e. force freeze_min_age and freeze_max_age to the
same min/max values as their GUC equivalents. Or at very least issue a
WARNING to the logs if a too-low value is present.

The docs should say "If you set autovacuum_freeze_age to 0 or a low
positive number this will cause the table to be constantly VACUUM
FREEZEd, which you might want, but you very probably don't".

  Simon Riggs

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