| From: | Philip Warner <pjw(at)rhyme(dot)com(dot)au> |
|---|---|
| To: | Thomas Lockhart <lockhart(at)alumni(dot)caltech(dot)edu>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Jules Bean <jules(at)jellybean(dot)co(dot)uk>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Constant propagation and similar issues |
| Date: | 2000-09-18 09:34:35 |
| Message-ID: | 3.0.5.32.20000918193435.02f8d210@mail.rhyme.com.au |
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| Lists: | pgsql-hackers |
At 19:05 18/09/00 +1000, Philip Warner wrote:
>
>I guess an alternative would be to define a special 'iscacheable' function:
>eg.
>
> function constant(arg <all-types>) returns <same-type-as-arg>
>
>so we could have:
>
> field < constant(current_timestamp - interval '1 hour')
>
>although this looks suspiciously like an optimizer hint which I think
>people have been opposed to in the past...
>
I just saw the flaw with this: iscacheable is not enough when the args are
deemed non-constant. I guess we'd need some kind of 'evaluate_once' flag,
which is getting a little obtuse.
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