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From: Greg Smith <greg@2ndquadrant.com>
To: Hannu Krosing <hannu@krosing.net>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Peter Hussey <peter@labkey.com>
Cc: pgsql-performance <pgsql-performance@postgresql.org>
Subject: Re: Questions on query planner, join types, and work_mem
Date: Wed, 04 Aug 2010 16:40:14 -0400
Message-ID: <4C59D02E.7040908@2ndquadrant.com> (raw)
In-Reply-To: <1280951504.3735.93.camel@hvost>
References: <AANLkTikMwVZKDYLitnsK31R=VNOuTH8NtmDHDGkBR7k8@mail.gmail.com>
	<18551.1280275502@sss.pgh.pa.us>
	<AANLkTimXMR0jMdw+66E4Xx=SqNV37Ne9WfkFjPFZVjbV@mail.gmail.com>
	<25534.1280498632@sss.pgh.pa.us>
	<AANLkTik3oY1=F_uC843c84LxBLNdHxZaWdfjxrAtyBeu@mail.gmail.com>
	<1280819031.14579.38.camel@hvost>
	<AANLkTik6UBt2ezVFzdCM8iaUPkra_7f-Hs_AmGZgvFhh@mail.gmail.com>
	<1280944268.3735.12.camel@hvost>
	<22961.1280944836@sss.pgh.pa.us>
	<1280947287.3735.56.camel@hvost>
	<1280948634.3735.69.camel@hvost>
	<4C59BCA8.2060603@2ndquadrant.com>
	<1280951504.3735.93.camel@hvost>

Hannu Krosing wrote:
> Do you mean "written to disk", or written out from shared_buffers to
> disk cache ?
>   

The later turns into the former eventually, so both really.  The kernel 
will do some amount of write combining for you if you're lucky.  But not 
in all cases; it may decide to write something out to physical disk 
before the second write shows up.

-- 
Greg Smith  2ndQuadrant US  Baltimore, MD
PostgreSQL Training, Services and Support
greg@2ndQuadrant.com   www.2ndQuadrant.us




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