To: pgsql-performance@postgresql.org
From: Ivan Voras <ivoras@freebsd.org>
Subject: Re: Performance under contention
Date: Mon, 22 Nov 2010 03:18:50 +0100
Lines: 20
Message-ID: <iccjub$bn0$1@dough.gmane.org>
References: <4CE9773D0200002500037CA6@gw.wicourts.gov>
Mime-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
User-Agent: Mozilla/5.0 (X11; U; FreeBSD amd64; en-US;
	rv:1.9.2.12) Gecko/20101102 Thunderbird/3.1.6
In-Reply-To: <4CE9773D0200002500037CA6@gw.wicourts.gov>

On 11/22/10 02:47, Kevin Grittner wrote:
> Ivan Voras  wrote:
>
>> After 16 clients (which is still good since there are only 12
>> "real" cores in the system), the performance drops sharply
>
> Yet another data point to confirm the importance of connection
> pooling.  :-)

I agree, connection pooling will get rid of the symptom. But not the 
underlying problem. I'm not saying that having 1000s of connections to 
the database is a particularly good design, only that there shouldn't be 
a sharp decline in performance when it does happen. Ideally, the 
performance should remain the same as it was at its peek.

I've been monitoring the server some more and it looks like there are 
periods where almost all servers are in the semwait state followed by 
periods of intensive work - approximately similar to the "thundering 
herd" problem, or maybe to what Josh Berkus has posted a few days ago.