| From: | PFC <lists(at)peufeu(dot)com> |
|---|---|
| To: | "Richard Huxton" <dev(at)archonet(dot)com>, "Luke Lonergan" <LLonergan(at)greenplum(dot)com> |
| Cc: | albert(at)sedifa(dot)com, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: Posible planner improvement? |
| Date: | 2008-05-21 16:18:27 |
| Message-ID: | op.ubih81yvcigqcu@apollo13.peufeu.com |
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| Lists: | pgsql-hackers pgsql-performance |
On Wed, 21 May 2008 15:09:49 +0200, Richard Huxton <dev(at)archonet(dot)com>
wrote:
> Luke Lonergan wrote:
>> The problem is that the implied join predicate is not being
>> propagated. This is definitely a planner deficiency.
>
> IIRC only equality conditions are propagated and gt, lt, between aren't.
> I seem to remember that the argument given was that the cost of
> checking for the ability to propagate was too high for the frequency
> when it ocurred.
>
> Of course, what was true for code and machines of 5 years ago might not
> be so today.
>
Suggestion : when executing a one-off sql statement, optimizer should try
to offer "best effort while being fast" ; when making a plan that will be
reused many times (ie PREPARE, functions...) planning time could be
muuuuch longer...
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