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Re: [WIP] Caching constant stable expressions per execution

From: Josh Berkus <josh(at)agliodbs(dot)com>
To: pgsql-hackers(at)postgresql(dot)org
Subject: Re: [WIP] Caching constant stable expressions per execution
Date: 2011-09-11 01:02:41
Message-ID: 4E6C08B1.1080804@agliodbs.com (view raw or flat)
Thread:
Lists: pgsql-hackers
> The patch as given has a bunch of implementation issues, but I think
> it's close enough for crude performance testing, and your numbers do
> show a potential performance benefit.  The question that I think is
> unresolved is whether the set of cases covered is wide enough to be
> useful in practice.  I have no data on that ...

Well, I think its use for timestamp/interval/casting functions alone
covers a pretty substantial set of common user actions.  Frankly, the
case of not re-evaluating now() alone would be a significant real-life
improvement.

If I understand the limitations correctly, though, what this would do is
cause functions to perform substantially differently if called with
expressions as arguments instead of text constants, no?  Seems like that
would lead to some user confusion.  Although, with stuff like now(), we
already have that.

-- 
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com

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