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Re: Wierd context-switching issue on Xeon

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: josh(at)agliodbs(dot)com
Cc: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>, pg(at)fastcrypt(dot)com,Robert Creager <Robert_Creager(at)LogicalChaos(dot)org>, Dirk_Lutzebäck <lutzeb(at)aeccom(dot)com>,ohp(at)pyrenet(dot)fr, Joe Conway <mail(at)joeconway(dot)com>,"scott(dot)marlowe" <scott(dot)marlowe(at)ihs(dot)com>,pgsql-performance(at)postgresql(dot)org, Neil Conway <neilc(at)samurai(dot)com>
Subject: Re: Wierd context-switching issue on Xeon
Date: 2004-05-20 22:14:52
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Josh Berkus <josh(at)agliodbs(dot)com> writes:
> I'm really curious, BTW, about how all of Jan's changes to buffer
> usage in 7.5 affect this issue.  Has anyone tested it on a recent
> snapshot?

Won't help.

(1) Theoretical argument: the problem case is select-only and touches
few enough buffers that it need never visit the kernel.  The buffer
management algorithm is thus irrelevant since there are never any
decisions for it to make.  If anything CVS tip will have a worse problem
because its more complicated management algorithm needs to spend longer
holding the BufMgrLock.

(2) Experimental argument: I believe that I did check the self-contained
test case we eventually developed against CVS tip on one of Red Hat's
SMP machines, and indeed it was unhappy.

			regards, tom lane

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