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From: Simon Riggs <simon@2ndQuadrant.com>
To: Matthew Wakeling <matthew@flymine.org>
Cc: Scott Carey <scott@richrelevance.com>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: Proposal of tunable fix for scalability of 8.4
Date: Sat, 21 Mar 2009 08:50:39 +0000
Message-ID: <1237625439.3953.539.camel@ebony.2ndQuadrant> (raw)
In-Reply-To: <alpine.DEB.2.00.0903201237050.21772@aragorn.flymine.org>
References: <alpine.GSO.2.01.0903121613270.1925@westnet.com>
	<C5DED7A7.33B2%scott@richrelevance.com>
	<603c8f070903121829r31cf1472ha9876e5c480a542e@mail.gmail.com>
	<12292.1236964604@sss.pgh.pa.us>
	<49BB699D.1070809@enterprisedb.com>
	<alpine.DEB.2.00.0903161543590.21772@aragorn.flymine.org>
	<1237362833.3953.186.camel@ebony.2ndQuadrant>
	<BDFBB77C9E07BE4A984DAAE981D19F961AEE7AFBB7@EXVMBX018-1.exch018.msoutlookonline.net>
	<alpine.DEB.2.00.0903201237050.21772@aragorn.flymine.org>


On Fri, 2009-03-20 at 15:28 +0000, Matthew Wakeling wrote:
> On Thu, 19 Mar 2009, Scott Carey wrote:
> > In type B, the ratio of requests that must context switch is always == 
> > 1.  Every request must queue and wait!
> 
> A remarkably good point, although not completely correct. Every request 
> that arrives when the lock is held in any way already will queue and wait. 
> Requests that arrive when the lock is free will run immediately. I admit 
> it, this is a killer for this particular locking strategy.

I think the right mix of theory and test here is for people to come up
with new strategies that seem to make sense and then we'll test them
all. Trying too hard to arrive at the best strategy purely through
discussion will mean we miss a few tricks. Feels like we're on the right
track here.

-- 
 Simon Riggs           www.2ndQuadrant.com
 PostgreSQL Training, Services and Support




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