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Re: Autovacuum and stats_row_level

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Chander Ganesan <chander(at)otg-nc(dot)com>
Cc: d(dot)wall(at)computer(dot)org, pgsql-general(at)postgresql(dot)org
Subject: Re: Autovacuum and stats_row_level
Date: 2008-01-30 04:32:01
Message-ID: 2270.1201667521@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-general
Chander Ganesan <chander(at)otg-nc(dot)com> writes:
> David Wall wrote:
>> Noted that to use autovacuum we need to turn on stats_row_level (along 
>> with stats_start_collector that is on by default).  Since 
>> stats_row_level is off by default, I wonder what sort of overhead is 
>> incurred since it sounds like it could add up if it's storing 
>> additional stats information on every row update, though it's not 
>> clear to me just what it means to have row level stats.

> There is overhead. I think it is somewhat related to your query load  
> However, I do know that there is some rate limiting logic in place to 
> prevent the backends from sending too many messages to the stats collector.

The rate-limit logic is new for 8.3, but it's always been true that at
most one message is sent per query (and in fact one per transaction,
in recent releases).

			regards, tom lane

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