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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Gregory Stark <stark@enterprisedb.com>
Cc: Alan Stange <stange@rentec.com>
Cc: Jignesh K. Shah <J.K.Shah@sun.com>
Cc: Greg Smith <gsmith@gregsmith.com>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: 8.4 Performance improvements: was Re: Proposal of tunable fix for scalability of 8.4
Date: Sat, 14 Mar 2009 11:52:05 -0400
Message-ID: <4861.1237045925@sss.pgh.pa.us> (raw)
In-Reply-To: <603c8f070903131937t1c33fa97k29e7d8d07fa2e83@mail.gmail.com>
References: <C5DDBB25.3333%scott@richrelevance.com>
	<49B922C0.6050700@sun.com>
	<alpine.GSO.2.01.0903121613270.1925@westnet.com>
	<49BA5537.8060002@sun.com>
	<87prgl4jbh.fsf@oxford.xeocode.com>
	<49BA79A4.9030208@rentec.com>
	<12431.1236965004@sss.pgh.pa.us>
	<87d4ck50h1.fsf@oxford.xeocode.com>
	<26666.1236996376@sss.pgh.pa.us>
	<603c8f070903131937t1c33fa97k29e7d8d07fa2e83@mail.gmail.com>

Robert Haas <robertmhaas@gmail.com> writes:
> On Fri, Mar 13, 2009 at 10:06 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> I assume you meant effective_io_concurrency.  We'd still need a special
>> case because the default is currently hard-wired at 1, not 0, if
>> configure thinks the function exists.

> I think 1 should mean no prefetching, rather than 0.

No, 1 means "prefetch a single block ahead".  It doesn't involve I/O
concurrency in the sense of multiple I/O requests being processed at
once; what it does give you is CPU vs I/O concurrency.  0 shuts that
down and returns the system to pre-8.4 behavior.

			regards, tom lane



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