From: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
---|---|
To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Speed up Clog Access by increasing CLOG buffers |
Date: | 2016-09-29 01:10:30 |
Message-ID: | d8dd08a9-1352-a34a-833b-6864780a4c53@2ndquadrant.com |
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Lists: | pgsql-hackers |
On 09/29/2016 01:59 AM, Robert Haas wrote:
> On Wed, Sep 28, 2016 at 6:45 PM, Tomas Vondra
> <tomas(dot)vondra(at)2ndquadrant(dot)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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