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Re: testing HS/SR - 1 vs 2 performance

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Simon Riggs <simon(at)2ndquadrant(dot)com>
Cc: Erik Rijkers <er(at)xs4all(dot)nl>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: testing HS/SR - 1 vs 2 performance
Date: 2010-04-23 15:32:19
Message-ID: j2q603c8f071004230832rdd1791c8pfedb6e2fd5c0468@mail.gmail.com (view raw or flat)
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On Fri, Apr 23, 2010 at 11:14 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> On Thu, 2010-04-22 at 23:45 +0100, Simon Riggs wrote:
>> On Thu, 2010-04-22 at 20:39 +0200, Erik Rijkers wrote:
>> > On Sun, April 18, 2010 13:01, Simon Riggs wrote:
>>
>> > any comment is welcome...
>>
>> Please can you re-run with -l and post me the file of times
>
> Erik has sent me details of a test run. My analysis of that is:
>
> I'm seeing the response time profile on the standby as
> 99% <110us
> 99.9% <639us
> 99.99% <615ms
>
> 0.052% (52 samples) are >5ms elapsed and account for 24 s, which is
> about 45% of elapsed time.
>
> Of the 52 samples >5ms, 50 of them are >100ms and 2 >1s.
>
> 99% of transactions happen in similar times between primary and standby,
> everything dragged down by rare but severe spikes.
>
> We're looking for something that would delay something that normally
> takes <0.1ms into something that takes >100ms, yet does eventually
> return. That looks like a severe resource contention issue.

Wow.  Good detective work.

...Robert

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