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Re: Constraint exclusion can't process simple constant expressions?

From: Claudio Freire <klaussfreire(at)gmail(dot)com>
To: Brendan Jurd <direvus(at)gmail(dot)com>
Cc: Josh Berkus <josh(at)agliodbs(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Constraint exclusion can't process simple constant expressions?
Date: 2011-04-21 07:30:36
Message-ID: BANLkTimvHBwg88a-WDxhz-=Ts6Ry6wNApQ@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Thu, Apr 21, 2011 at 4:05 AM, Brendan Jurd <direvus(at)gmail(dot)com> wrote:
>
> "IMMUTABLE indicates that the function cannot modify the database and
> always returns the same result when given the same argument values"
>
> Emphasis on "always".  If the result of the function, given the same
> argument values, can be different after a SET, then it doesn't qualify
> for immutability.  At least, that's my understanding.

That's a ridiculous use of the word "Immutable"

In any CS class, the timezone would be an implicit input to the
function. So it would be immutable in *that* sense (it also takes
timezone into consideration).

Perhaps the optimizer should take contextual information that cannot
change inside a query as input too.

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Subject: Re: Constraint exclusion can't process simple constant expressions?
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