Message-ID: <49A44509.6090600@gmail.com>
Date: Tue, 24 Feb 2009 20:05:45 +0100
From: Stefano Nichele <stefano.nichele@gmail.com>
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To: Alvaro Herrera <alvherre@commandprompt.com>
CC: pgsql-admin@postgresql.org
Subject: Re: strange autovacuum behaviour
References: <49906B4F.5040509@gmail.com>
 <20090210140742.GG3708@alvh.no-ip.org>
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Hi Alvaro,
thanks for your answer and sorry for the delay but I was in vacation.

Alvaro Herrera wrote:
> Stefano Nichele escribió:
>   
>> Hi All,
>> I have a couple of questions about autovacuum/vacuum behavior.
>>
>> On my production system, I set autovacuum ON since it's pretty hard to
>> me find a good timeframe for vacuum (the system is pretty busy over the day)
>> Last week the system was really slow and running vacuum manually the
>> performance was really improved.
>> So now I would like to understand why autovacuum did not work as
>> expected (at least for me). Any ideas ?
>>     
>
> Maybe the autovacuum naptime was set too high.  Or perhaps the threshold
> and scale settings were too high.  Maybe the vacuum_cost_delay for
> autovacuum was too high.
>   
Currently I'm still run vacuum but as soon as I can, I'll do other tests.
>   
>> Why autovacuum (that was OFF) started ?  For preventing transaction ID
>> wraparound ? Is it right that in such case all the tables are
>> (auto)vacuumed ?
>>     
>
> Not necessarily all tables; only those that require a vacuum to prevent
> xid wraparound.  (It was all tables in 8.1, but this changed in 8.2).
>
>   
Actually I saw that it autovacuumed all tables (except 2 of 100 tables). 
And why during vacuum ? (this is not just a coincidence since occurred 
more than one time).
It seems autovacuum was triggered by vacuum.

Cheers,
ste