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Re: Help tuning autovacuum - seeing lots of relationbloat

From: "jody brownell" <jody(dot)brownell(at)q1labs(dot)com>
To: "Csaba Nagy" <nagy(at)ecircle-ag(dot)com>
Cc: "postgres performance list" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Help tuning autovacuum - seeing lots of relationbloat
Date: 2006-06-21 16:39:33
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
that is exactly what I am seeing, one process, no change, always in idle while the others are constantly
changing their state.

looks like someone opened a tx then is blocking on a queue lock or something. dang.

On Wednesday 21 June 2006 13:36, Csaba Nagy wrote:
> On Wed, 2006-06-21 at 18:21, jody brownell wrote:
> > That is interesting.
> > 
> > There is one thread keeping a transaction open it appears from ps
> > 
> > postgres: app app xxx(42644) idle in transaction
> That shouldn't be a problem on itself, "idle in transaction" happens all
> the time between 2 commands in the same transaction... you only have a
> problem if you see the same PID always "idle", that means somebody left
> an open transaction and left for lunch.
> [snip]
> > this was with the "Idle in transaction" though..... 
> This probably means you don't have long running transactions currently.
> However, if you happen to have just one such long transaction, the dead
> space accumulates and normal vacuum will not be able to clean that
> anymore. But I guess if you didn't find one now then you should take a
> look at Tom's suggestion and bump up debug level to see if autovacuum
> picks your table at all...
> > Ah HA! Wondering, my autovacuum naptime is 60 seconds, that is also the interval which I wake up and begin persistence.
> > Wondering if I am simply locking autovacuum out of the tables b/c they are on a similar timeline.
> > 
> > I will try a 30 second naptime, if this is it, that should increase the likely hood of falling on the right side of the TX more often.
> > 
> > make sense?
> I don't think that's your problem... vacuum wouldn't be locked out by
> any activity which doesn't lock exclusively the table (and I guess
> you're not doing that). If your persistence finishes quickly then that's
> not the problem.
> Oh, just occured to me... in order to use autovacuum you also need to
> enable the statistics collector on row level:
> stats_start_collector = on
> stats_row_level = on
> See also:
> This was not mentioned in the settings in your original post, so I guess
> you didn't touch that, and I think they are disabled by default.
> If this is disabled, you should enable it and "pg_ctl reload ....", that
> should fix the problem.
> Cheers,
> Csaba.

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