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From: Greg Smith <greg@2ndquadrant.com>
To: Kevin Grittner <Kevin.Grittner@wicourts.gov>
Cc: Hannu Krosing <hannu@2ndquadrant.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Peter Hussey <peter@labkey.com>
Cc: pgsql-performance <pgsql-performance@postgresql.org>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Subject: Re: Questions on query planner, join types, and	 work_mem
Date: Wed, 04 Aug 2010 16:38:32 -0400
Message-ID: <4C59CFC8.4000701@2ndquadrant.com> (raw)
In-Reply-To: <4C59800002000025000341F7@gw.wicourts.gov>
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>
	<4C59800002000025000341F7@gw.wicourts.gov>

Kevin Grittner wrote:
> Assuming this is real, and not just "in the noise" -- what conclusions would you
> draw from this?

Was trying to demonstrate the general ability of pg_stat_bgwriter 
snapshots at points in time to directly measure the buffer activity 
Hannu was theorizing about, not necessarily show a useful benchmark of 
any sort with that.  Watching pgbench create a database isn't all that 
interesting unless you either a) increase the database scale such that 
at least one timed checkpoint kicks in, or b) turn on archive_mode so 
the whole WAL COPY optimization is defeated.  More on this topic later, 
just happened to have that little example script ready to demonstrate 
the measurement concept.

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




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