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Re: dynamic SQL - possible performance regression in 9.2

From: "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>
To: Josh Berkus <josh(at)agliodbs(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: dynamic SQL - possible performance regression in 9.2
Date: 2013-01-04 20:26:12
Message-ID: 50E73AE4.9000600@commandprompt.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On 01/04/2013 12:05 PM, Josh Berkus wrote:
>
>
>> Next question is what people think about back-patching into 9.2 so as
>> to eliminate the performance regression vs 9.1.  I believe this would
>> be safe (although some care would have to be taken to put the added
>> boolean fields into places where they'd not result in an ABI break).
>> However it may not be worth the risk.  The 40% slowdown seen with
>> Pavel's example seems to me to be an extreme corner case --- Dong's
>> result of 8% slowdown is probably more realistic for normal uses
>> of SPI_execute.  Might be better to just live with it in 9.2.
>> Thoughts?
>
> 8% is a pretty serious regression, for those of us with applications
> which do a lot of dynamic SQL.  As a reminder, many people do dynamic
> SQL even in repetitive, performance-sensitive functions in order to
> avoid plan caching.   Also partition-handlers often use dynamic SQL, and
> a 10% drop in loading rows/second would be a big deal.
>
> Let's put it this way: if the community doesn't backport it, we'll end
> up doing so ad-hoc for some of our customers.

Exactly. This is a significant reduction in the production quality of 
PostgreSQL as it pertains to dynamic SQL. To put it more bluntly, we 
will have people not upgrade to 9.2 specifically because of this problem.

Joshua D. Drake



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