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From: Florian G. Pflug <fgp@phlo.org>
To: Kevin Grittner <Kevin.Grittner@wicourts.gov>
Cc: Simon Riggs <simon@2ndquadrant.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Hint Bits and Write I/O
Date: Fri, 30 May 2008 10:42:34 +0200
Message-ID: <483FBDFA.4090401@phlo.org> (raw)
In-Reply-To: <483EE689.EE98.0025.0@wicourts.gov>
References: <1211916951.4489.232.camel@ebony.site>
	<483C7CE8.2090404@phlo.org>
	<1211926242.4489.301.camel@ebony.site>
	<1211926242.4489.301.camel@ebony.site>
	<483DEA2D.3010704@phlo.org>
	<483EE689.EE98.0025.0@wicourts.gov>

Kevin Grittner wrote:
>>>> On Wed, May 28, 2008 at  6:26 PM, in message
> <483DEA2D.3010704@phlo.org>,
> "Florian G. Pflug" <fgp@phlo.org> wrote: 
>  
>> I think we should put some randomness into the decision,
>> to spread the IO caused by hit-bit updates after a batch load.
>  
> Currently we have a policy of doing a VACUUM FREEZE ANALYZE on a table
> after a bulk load, or on the entire database after loading a pg_dump
> of a database.  We do this before putting the table or database into
> production.  This avoids surprising clusters of writes at
> unpredictable times.  Please don't defeat that.  (I'm not sure whether
> your current suggestion would.)

No, VACUUM (and therefore VACUUM FREEZE) dirty all buffers they set hit 
bits on anyway, since they also update the xmin values. But a more 
IO-friendly approach to setting hit bits might make that VACUUM FREEZE 
step unnecessary ;-)

regards, Florian Pflug



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