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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>
Cc: Dilip Kumar <dilipbalaut@gmail.com>
Cc: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Speed up Clog Access by increasing CLOG buffers
Date: Thu, 29 Sep 2016 03:10:30 +0200
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On 09/29/2016 01:59 AM, Robert Haas wrote:
> On Wed, Sep 28, 2016 at 6:45 PM, Tomas Vondra
> <tomas.vondra@2ndquadrant.com> wrote:
>> So, is 300 too little? I don't think so, because Dilip saw some benefit from
>> that. Or what scale factor do we think is needed to reproduce the benefit?
>> My machine has 256GB of ram, so I can easily go up to 15000 and still keep
>> everything in RAM. But is it worth it?
>
> Dunno. But it might be worth a test or two at, say, 5000, just to
> see if that makes any difference.
>

OK, I have some benchmarks to run on that machine, but I'll do a few 
tests with scale 5000 - probably sometime next week. I don't think the 
delay matters very much, as it's clear the patch will end up with RwF in 
this CF round.

> I feel like we must be missing something here.  If Dilip is seeing
> huge speedups and you're seeing nothing, something is different, and
> we don't know what it is.  Even if the test case is artificial, it
> ought to be the same when one of you runs it as when the other runs
> it.  Right?
>

Yes, definitely - we're missing something important, I think. One 
difference is that Dilip is using longer runs, but I don't think that's 
a problem (as I demonstrated how stable the results are).

I wonder what CPU model is Dilip using - I know it's x86, but not which 
generation it is. I'm using E5-4620 v1 Xeon, perhaps Dilip is using a 
newer model and it makes a difference (although that seems unlikely).

regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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