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Re: strange fsm issues

From: "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com>
To: Jeff Frost <jeff(at)frostconsultingllc(dot)com>
Cc: pgsql-admin(at)postgresql(dot)org
Subject: Re: strange fsm issues
Date: 2006-06-28 04:45:29
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Lists: pgsql-admin
On Tue, Jun 27, 2006 at 08:02:33PM -0700, Jeff Frost wrote:
> On Tue, 27 Jun 2006, Jim Nasby wrote:
> >>What the heck?  Why would it have shrunk down so much?  The vacuum full 
> >>isn't scheduled until tonight. :-/
> >
> >Take a look at the source for autovacuum... I'm guessing you're right and 
> >that it doesn't make any special considerations for toast tables, which it 
> >probably should (since AFAIK you have to first vacuum the base table, then 
> >commit, then vacuum the toast table).
> >
> >BTW, tracking pg_class.relpages or actual file size over time would 
> >probably be helpful.
> Actually, it says this:
> /*
> * Scan pg_class and determine which tables to vacuum.
> *
> * The stats subsystem collects stats for toast tables independently of
> * the stats for their parent tables.  We need to check those stats since
> * in cases with short, wide tables there might be proportionally much
> * more activity in the toast table than in its parent.
> *
> * Since we can only issue VACUUM against the parent table, we need to
> * transpose a decision to vacuum a toast table into a decision to vacuum
> * its parent.  There's no point in considering ANALYZE on a toast table,
> * either.      To support this, we keep a list of OIDs of toast tables that
> * need vacuuming alongside the list of regular tables.  Regular tables
> * will be entered into the table list even if they appear not to need
> * vacuuming; we go back and re-mark them after finding all the vacuumable
> * toast tables.
> */
> So I guess it does take toast tables into account.

Only if it issues 2 vacuums on the base tables...
Jim C. Nasby, Sr. Engineering Consultant      jnasby(at)pervasive(dot)com
Pervasive Software    work: 512-231-6117
vcard:       cell: 512-569-9461

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Next:From: Jim C. NasbyDate: 2006-06-28 04:47:38
Subject: Re: 8.1.3 - autovacuum question
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Subject: Re: strange fsm issues

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