Message-ID: <46D840EC.1060302@livedatagroup.com>
Date: Fri, 31 Aug 2007 12:25:16 -0400
From: Pallav Kalva <pkalva@livedatagroup.com>
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To: Alvaro Herrera <alvherre@commandprompt.com>
CC: Tom Lane <tgl@sss.pgh.pa.us>,  pgsql-performance@postgresql.org
Subject: Re: 8.2 Autovacuum BUG ?
References: <46D83427.60001@livedatagroup.com>
 <25038.1188574775@sss.pgh.pa.us>
	<46D83C50.3040409@livedatagroup.com>
	<20070831161158.GD8046@alvh.no-ip.org>
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Alvaro Herrera wrote:
> 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.
>
>   
Can you please correct me if I am wrong, I want to understand how this 
works.
Based on what you said, it will run autovacuum again when it passes 200M 
transactions, as SELECTS are transactions too and are going on these 
tables.
But the next time when it runs autovacuum, it shouldnt freeze the tuples 
again as they are already frozen and wont generate lot of archive logs ?
Or is this because of it ran autovacuum for the first time on this db ? 
just the first time it does this process ?