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Date: Wed, 11 Mar 2009 22:20:17 -0400
From: "Jignesh K. Shah" <J.K.Shah@Sun.COM>
Subject: Re: Proposal of tunable fix for scalability of 8.4
In-reply-to: <29080.1236821556@sss.pgh.pa.us>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Kevin Grittner <Kevin.Grittner@wicourts.gov>,
	pgsql-performance@postgresql.org
Message-id: <49B87161.10201@sun.com>
References: <49B824DD.7090302@sun.com> <49B7F470.EE98.0025.0@wicourts.gov>
	<29080.1236821556@sss.pgh.pa.us>
User-Agent: Thunderbird 2.0.0.19 (Macintosh/20081209)


Tom Lane wrote:
> "Kevin Grittner" <Kevin.Grittner@wicourts.gov> writes:
>   
>> I'm wondering about the testing methodology.
>>     
>
> Me too.  This test case seems much too far away from real world use
> to justify diddling low-level locking behavior; especially a change
> that is obviously likely to have very negative effects in other
> scenarios.  In particular, I think it would lead to complete starvation
> of would-be exclusive lockers in the face of competition from a steady
> stream of shared lockers.  AFAIR the existing behavior was designed
> to reduce the odds of that, not for any other purpose.
>
> 			regards, tom lane
>
>   

Hi Tom,

The test case is not that far fetched from real world.. Plus if you read 
my proposal I clearly mention a tunable for it so that we can set and 
hence obviously not impact 99% of the people who don't care about it but 
still allow the flexibility of the 1% of the people who do care about 
scalability when they go on bigger system. The fact that it is a tunable 
(and obviously not the default way) there is no impact to existing 
behavior.

My test case clearly shows that Exclusive lockers ARE benefited from it 
otherwise I would have not seen the huge impact on throughput.

A tunable does not impact existing behavior but adds flexibility for 
those using PostgreSQL on high end systems. Plus doing it the tunable 
way on PostgreSQL 8.4 will convince many people that I know to quickly 
adopt PostgreSQL 8.4 just because of the benefit it brings on systems 
with many cpus/cores/threads.

All I am requesting is for the beta to have that tunable. Its not hard, 
people can then quickly try default (off) or on or as Scott Carey 
mentioned  a more flexible of default, all or a fixed integer number 
(for people to experiment).


Regards,
Jignesh

-- 
Jignesh Shah           http://blogs.sun.com/jkshah  			
The New Sun Microsystems,Inc   http://sun.com/postgresql