To: pgsql-performance@postgresql.org
From: Ivan Voras <ivoras@freebsd.org>
Subject: Re: Performance under contention
Date: Thu, 25 Nov 2010 13:39:42 +0100
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On 11/22/10 18:47, Kevin Grittner wrote:
> Ivan Voras<ivoras@freebsd.org>  wrote:
>
>> It looks like a hack
>
> Not to everyone.  In the referenced section, Hellerstein,
> Stonebraker and Hamilton say:
>
> "any good multi-user system has an admission control policy"
>
> In the case of PostgreSQL I understand the counter-argument,
> although I'm inclined to think that it's prudent for a product to
> limit resource usage to a level at which it can still function well,
> even if there's an external solution which can also work, should
> people use it correctly.  It seems likely that a mature admission
> control policy could do a better job of managing some resources than
> an external product could.

I didn't think it would be that useful but yesterday I did some 
(unrelated) testing with MySQL and it looks like its configuration 
parameter "thread_concurrency" does something to that effect.

Initially I thought it is equivalent to PostgreSQL's max_connections but 
no, connections can grow (MySQL spawns a thread per connection by 
default) but the actual concurrency is limited in some way by this 
parameter.

The comment for the parameter says "# Try number of CPU's*2 for 
thread_concurrency" but obviously it would depend a lot on the 
real-world load.