Re: [PERFORM] optimizing immutable vs. stable function calls? - Mailing list pgsql-performance

From Jim Nasby
Subject Re: [PERFORM] optimizing immutable vs. stable function calls?
Date
Msg-id 74793a73-20ac-0e1f-bb61-cafe6b3371cf@BlueTreble.com
Whole thread Raw
In response to Re: [PERFORM] optimizing immutable vs. stable function calls?  ("David G. Johnston" <david.g.johnston@gmail.com>)
Responses Re: [PERFORM] optimizing immutable vs. stable function calls?  (Merlin Moncure <mmoncure@gmail.com>)
List pgsql-performance
On 1/18/17 6:09 PM, David G. Johnston wrote:
> ​That would not be a productive exercise for me, or most people who just
> want
> some idea of what to expect in terms of behavior when they write and use a
> Stable function (Immutable and Volatile seem fairly easy to reason about).

Yeah, this isn't an uncommon question for users to have, and "read the
code" isn't a great answer.

If there's a README or comment block that describes this, that might be
a reasonable compromise.

It would certainly be useful to document how to push the planner in the
right direction as well. I didn't realize that SELECT ... (SELECT
slow_stable_function()) was a thing until reading this thread.
--
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com
855-TREBLE2 (855-873-2532)


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