| From: | Jim Nasby <Jim(dot)Nasby(at)BlueTreble(dot)com> |
|---|---|
| To: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Karl Czajkowski <karlcz(at)isi(dot)edu>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: optimizing immutable vs. stable function calls? |
| Date: | 2017-01-23 15:10:00 |
| Message-ID: | 74793a73-20ac-0e1f-bb61-cafe6b3371cf@BlueTreble.com |
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| Lists: | 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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