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From: David Boreham <david_list@boreham.org>
To: Alexander Staubo <alex@purefiction.net>
Cc: Michael Stone <mstone+postgres@mathom.us>
Cc: pgsql-performance@postgresql.org
Subject: Re: New to PostgreSQL, performance considerations
Date: Tue, 12 Dec 2006 08:58:21 -0700
Message-ID: <457ED19D.7050301@boreham.org> (raw)
In-Reply-To: <42B14BCF-B745-4F94-B5EA-97997744A4D5@purefiction.net>
References: <8a0c7af10612110531sbb019ck259fb16d131fdb50@mail.gmail.com>
	<60psaq5t94.fsf@dba2.int.libertyrms.com>
	<E1GtolA-0008Fk-4R@elasmtp-banded.atl.sa.earthlink.net>
	<20061211173105.GH16692@mathom.us>
	<E1Gtplp-0004Ka-GM@elasmtp-junco.atl.sa.earthlink.net>
	<20061211184726.GI16692@mathom.us>
	<E1GtrB8-0005rw-Iu@elasmtp-kukur.atl.sa.earthlink.net>
	<457DA782.3060506@modgraph-usa.com>
	<8a0c7af10612111422x6bdcc0c2p7cbfeb5a7b0e0374@mail.gmail.com>
	<2FC0D8E7-F8ED-452F-BB13-FB665B516E7F@purefiction.net>
	<20061212123252.GR16692@mathom.us>
	<42B14BCF-B745-4F94-B5EA-97997744A4D5@purefiction.net>

Alexander Staubo wrote:

> No, fsync=on. The tps values are similarly unstable with fsync=off,  
> though -- I'm seeing bursts of high tps values followed by low-tps  
> valleys, a kind of staccato flow indicative of a write caching being  
> filled up and flushed.

Databases with checkpointing typically exhibit this cyclical throughput 
syndrome.
(put another way : this is to be expected and you are correct that it 
indicates buffered
data being flushed to disk periodically).

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