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From: Andres Freund <andres@2ndquadrant.com>
To: Josh Berkus <josh@agliodbs.com>
Cc: Andrew Dunstan <andrew@dunslane.net>
Cc: Jeff Janes <jeff.janes@gmail.com>
Cc: Amit Kapila <amit.kapila@huawei.com>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: Performance bug in prepared statement binding in 9.2?
Date: Wed, 11 Sep 2013 23:12:53 +0200
Message-ID: <20130911211253.GF1138556@alap2.anarazel.de> (raw)
In-Reply-To: <5230B801.90507@agliodbs.com>
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	<20130910122036.GF1024477@alap2.anarazel.de>
	<522F146D.2070908@dunslane.net>
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On 2013-09-11 11:35:45 -0700, Josh Berkus wrote:
> All,
> 
> We've confirmed that this issue is caused by having long-running idle
> transactions on the server.  When we disabled their queueing system
> (which prodiced hour-long idle txns), the progressive slowness went away.
> 
> Why that should affect 9.X far more strongly than 8.4, I'm not sure
> about.  Does that mean that 8.4 was unsafe, or that this is something
> which *could* be fixed in later versions?

The explanation is in
http://archives.postgresql.org/message-id/20130910132133.GJ1024477%40alap2.anarazel.de

The referenced commit introduced a planner feature. Funnily you seem to
have been the trigger for it's introduction ;)

> I'm also confused as to why this would affect BIND time rather than
> EXECUTE time.

Because we're doing the histogram checks during planning and not during
execution.

Greetings,

Andres Freund

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


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