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Re: Proposal of tunable fix for scalability of 8.4

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: "Jignesh K(dot) Shah" <J(dot)K(dot)Shah(at)sun(dot)com>
Cc: Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Scott Carey <scott(at)richrelevance(dot)com>, Greg Smith <gsmith(at)gregsmith(dot)com>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Proposal of tunable fix for scalability of 8.4
Date: 2009-03-21 00:45:28
Message-ID: 603c8f070903201745m575642f5s539e1a374ce4ce9f@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Fri, Mar 20, 2009 at 7:39 PM, Jignesh K. Shah <J(dot)K(dot)Shah(at)sun(dot)com> wrote:
> Alvaro Herrera wrote:
>>> So Simon's correct.
>> And perhaps this explains why Jignesh is measuring an improvement on his
>> benchmark.  Perhaps an useful experiment would be to turn this behavior
>> off and compare performance.  This lack of measurement is probably the
>> cause that the suggested patch to fix it was never applied.
>>
>> The patch is here
>> http://archives.postgresql.org//pgsql-hackers/2004-11/msg00935.php
>
> One of the reasons why my patch helps is it keeps this check intact but
> allows other exclusive Wake up.. Now what PostgreSQL calls "Wakes" is  in
> reality just makes a variable indicating wake up and not really signalling a
> process to wake up. This is a key point to note. So when the process wanting
> the exclusive fights the OS Scheduling policy to finally get time on the CPU
> then it   check the value to see if it is allowed to wake up and potentially

I'm confused.  Is a process waiting for an LWLock is in a runnable
state?  I thought we went to sleep on a semaphore.

...Robert

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