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Re: 8.2 Autovacuum BUG ?

From: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
To: Pallav Kalva <pkalva(at)livedatagroup(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-performance(at)postgresql(dot)org
Subject: Re: 8.2 Autovacuum BUG ?
Date: 2007-08-31 16:11:58
Message-ID: 20070831161158.GD8046@alvh.no-ip.org (view raw or flat)
Thread:
Lists: pgsql-performance
Pallav Kalva wrote:
> Tom Lane wrote:

>> Probably represents freezing of old tuples, which is a WAL-logged
>> operation as of 8.2.  Is it likely that the data is 200M transactions
>> old?
>>   
> If nothing changed on these tables how can it freeze old tuples ?
> Does it mean that once it reaches 200M transactions it will do the same 
> thing all over again ?

No -- once tuples are frozen, they don't need freezing again (unless
they are modified by UPDATE or DELETE).

> If I am doing just SELECTS on these tables ? how can there be any 
> transactions ? or SELECTS considered transactions too ?

Selects are transactions too.  They just don't modify data.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

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