Date: Fri, 10 Aug 2007 13:54:41 -0400
From: "Jignesh K. Shah" <J.K.Shah@Sun.COM>
Subject: Re: CLOG Patch
In-reply-to: <1186172987.4136.18.camel@ebony.site>
To: Simon Riggs <simon@2ndquadrant.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Josh Berkus <josh@agliodbs.com>,
	pgsql-performance@postgresql.org,
	Alvaro Herrera <alvherre@commandprompt.com>
Message-id: <46BCA661.6000404@sun.com>
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References: <200707190828.59088.josh@agliodbs.com>
	<200707191819.13899.josh@agliodbs.com> <15685.1184895926@sss.pgh.pa.us>
	<200707192138.39679.josh@agliodbs.com> <46A0FA31.2080208@sun.com>
	<12002.1184955831@sss.pgh.pa.us> <46A1055F.9010304@sun.com>
	<12445.1184958793@sss.pgh.pa.us> <46A11116.5030905@sun.com>
	<14909.1184962561@sss.pgh.pa.us> <46A1205B.8010205@sun.com>
	<15343.1184965054@sss.pgh.pa.us> <1185180668.4284.149.camel@ebony.site>
	<23848.1185199901@sss.pgh.pa.us> <1185201556.4284.243.camel@ebony.site>
	<25095.1185202498@sss.pgh.pa.us> <1185205663.4284.249.camel@ebony.site>
	<1185212261.4284.270.camel@ebony.site> <1545.1185214760@sss.pgh.pa.us>
	<46A7D5AD.9000706@sun.com> <13162.1185405865@sss.pgh.pa.us>
	<46A8AFDF.3050804@sun.com> <26825.1185460816@sss.pgh.pa.us>
	<46A8BD62.2080904@sun.com> <1185465076.4190.87.camel@ebony.site>
	<46B38B83.1000906@sun.com> <1186172987.4136.18.camel@ebony.site>
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I tried with CLOG  24 also and I got linear performance upto 1250 users 
after which it started to tank. 32 got us to 1350 users before some 
other bottleneck overtook it.


Based on what Tom said earlier, it might then make sense to make it a 
tunable with the default of 8 but something one can change for high 
number of users.


Thanks.
Regards,
Jignesh


Simon Riggs wrote:
> On Fri, 2007-08-03 at 16:09 -0400, Jignesh K. Shah wrote:
>
>   
>> This patch seems to work well (both with 32 and 64 value but not with 16 
>> and the default 8). 
>>     
>
> Could you test at 24 please also? Tom has pointed out the additional
> cost of setting this higher, even in workloads that don't benefit from
> the I/O-induced contention reduction.
>
>   
>> Is there a way we can integrate this in 8.3?
>>     
>
> I just replied to Josh's thread on -hackers about this.
>
>   
>> This will improve out of box performance quite a bit for high number of 
>> users (atleat 30% in my OLTP test)
>>     
>
> Yes, thats good. Will this have a dramatic effect on a particular
> benchmark, or for what reason might we need this? Tom has questioned the
> use case here, so I think it would be good to explain a little more for
> everyone. Thanks.
>
>