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From: Andres Freund <andres@2ndquadrant.com>
To: Josh Berkus <josh@agliodbs.com>
Cc: Jeff Janes <jeff.janes@gmail.com>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: Planner performance extremely affected by an hanging transaction (20-30 times)?
Date: Fri, 27 Sep 2013 23:14:39 +0200
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On 2013-09-27 13:57:02 -0700, Josh Berkus wrote:
> Andres, Jeff,
> 
> 
> >> As far as I can tell, the only downside of doing that is that, since hint
> >> bits might be set later, it is possible some dirty pages will get written
> >> unhinted and then re-dirtied by the hint bit setting, when more aggressive
> >> setting would have only one combined dirty write instead.  But that seems
> >> rather hypothetical, and if it really is a problem we should probably
> >> tackle it directly rather than by barring other optimizations.
> > 
> > I am - as evidenced - too tired to think about this properly, but I
> > think you might be right here.
> 
> Any thoughts on a fix for this we could get into 9.2.5?

I don't see much chance to apply anything like this in a
backbranch. Changing IO patterns in a noticeable way in a minor release
is just asking for trouble.

Also, this really isn't going to fix the issue discussed here - this was
just about the additional ProcArrayLock contention. I don't think it
would change anything dramatical in your case.

Greetings,

Andres Freund

-- 
 Andres Freund	                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services


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