Message-ID: <45B88680.4040500@oss.ntt.co.jp>
Date: Thu, 25 Jan 2007 19:29:20 +0900
From: Galy Lee <lee.galy@oss.ntt.co.jp>
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To: pgsql-performance@postgresql.org
CC: jim@nasby.net
Subject: Re: how to plan for vacuum?
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 <20070125033917.GD64372@nasby.net>
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Jim C. Nasby wrote:
> On Wed, Jan 24, 2007 at 02:37:44PM +0900, Galy Lee wrote:
>> 1.  How do we know if autovacuum is enough for my application, or should
>>     I setup a vacuum manually from cron for my application?
> 
> Generally I trust autovac unless there's some tables where it's critical
> that they be vacuumed frequently, such as a queue table or a web session
> table.

So how much can we trust autovac? I think at least the following cases 
can not be covered by autovac now:
  - small but high update tables which are sensitive to garbage
  - very big tables which need a long time to be vacuumed.
  - when we need to adjust the the max_fsm_page

>> 2. How to set the GUC parameters for autovacuum?
>> There are two sets of parameters for autovacuum:
>>     - vacuum threshold and scale factor (500/0.2)
>> ?$B!!  - analyze threshold and scale factor(250/0.1)
>> Is there any guideline to set these parameters?  When does it need to
>> change the default values?
> 
> I find those are generally pretty good starting points; just bear in
> mind that it means 20% dead space.

so what is the principle to set them?
  - keep dead space lower than some disk limit
  - or keep the garbage rate lower than fillfactor
  or any other general principle?