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Re: set autovacuum=off

From: Andy Colson <andy(at)squeakycode(dot)net>
To: Thom Brown <thom(at)linux(dot)com>
Cc: Alessandro Gagliardi <alessandro(at)path(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: set autovacuum=off
Date: 2012-02-23 15:18:35
Message-ID: 4F4658CB.3030505@squeakycode.net (view raw or flat)
Thread:
Lists: pgsql-performance
On 2/23/2012 6:34 AM, Thom Brown wrote:
> On 22 February 2012 23:50, Alessandro Gagliardi<alessandro(at)path(dot)com>  wrote:
>> I have a database where I virtually never delete and almost never do
>> updates. (The updates might change in the future but for now it's okay to
>> assume they never happen.) As such, it seems like it might be worth it to
>> set autovacuum=off or at least make it so vacuuming hardly ever occurs.
>> Actually, the latter is probably the more robust solution, though I don't
>> know how to do that (hence me writing this list). I did try turning
>> autovacuum off but got:
>>
>> ERROR: parameter "autovacuum" cannot be changed now
>> SQL state: 55P02
>>
>> Not sure what, if anything, I can do about that.
>
> Autovacuum is controlled by how much of a table has changed, so if a
> table never changes, it never gets vacuumed (with the exceptional case
> being a forced vacuum freeze to mitigate the transaction id
> wrap-around issue).  The settings which control this are
> autovacuum_vacuum_threshold and autovacuum_vacuum_scale_factor.
> Therefore it isn't necessary to disable autovacuum.
>
> But if you are adamant about disabling it, you need to change it in
> your postgresql.conf file and restart the server.
>

Agreed, don't disable autovacuum.  It's not that demanding, and if you 
do need it and forget to run it, it might cause you more problems.

I have a db that's on a VM that doesnt get hit very much.  I've noticed 
IO is a little busy (we are talking small percents of percents less than 
one) but still more that I thought should be happening on a db with next 
to no usage.

I found setting autovacuum_naptime = 6min made the IO all but vanish.

And if I ever get a wild hair and blow some stuff away, the db will 
clean up after me.

-Andy

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Subject: Re: Very long deletion time on a 200 GB database
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