To: Greg Smith <greg@2ndquadrant.com>
cc: Peter Koczan <pjkoczan@gmail.com>, pgsql-admin@postgresql.org
Subject: Re: Is regular vacuuming with autovacuum needed? 
In-reply-to: <4C6996CB.9090808@2ndquadrant.com> 
References: <AANLkTik63hP0v1wpstYJptr_ixiHaMjCF3tNpK+5XOZW@mail.gmail.com>
	<19036.1281983716@sss.pgh.pa.us> <4C6996CB.9090808@2ndquadrant.com>
Comments: In-reply-to Greg Smith <greg@2ndquadrant.com>
	message dated "Mon, 16 Aug 2010 15:51:39 -0400"
Date: Mon, 16 Aug 2010 16:01:24 -0400
Message-ID: <20665.1281988884@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Greg Smith <greg@2ndquadrant.com> writes:
> Tom Lane wrote:
>> On versions where autovacuum is on by default, I would certainly
>> recommend trying to use only autovacuum.  cron-driven vacuum still
>> has some uses but they are corner cases.

> Corner cases implies something a bit more rare than I'd consider the 
> case here.

Well, it certainly has some uses, but I still think it's good advice to
first see if autovac alone will keep you happy.

> The other alternative here is to just tune autovacuum so it runs really 
> slowly, so it won't kill responsiveness during any peak period.  While 
> in theory that's the right thing to do, this is much harder to get 
> working well than what I just described.

But you really have to do that *anyway*, if you're not going to turn
autovac off.

I think the case where you want to combine cron-driven vacuum with
autovac is where, having made sure autovac is dialed down enough to not
present performance issues, you find that it can't keep up with the
required vacuuming.  Then you need to do some not-hobbled vacuuming
during your maintenance windows.  Eventually probably autovac will have
some understanding of maintenance windows built-in, but it doesn't yet.

			regards, tom lane