| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | "Florian G(dot) Pflug" <fgp(at)phlo(dot)org> |
| Cc: | Rod Taylor <pg(at)rbt(dot)ca>, Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org, Martin Lesser <ml-pgsql(at)bettercom(dot)de> |
| Subject: | Re: "Constraint exclusion" is not general enough |
| Date: | 2006-08-08 02:01:15 |
| Message-ID: | 24484.1155002475@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
"Florian G. Pflug" <fgp(at)phlo(dot)org> writes:
> Tom Lane wrote:
>> But you don't have any cost numbers until after you've done the plan.
> Couldn't this work similar to geqo_effort? The planner could
> try planning the query using only cheap algorithmns, and if
> the cost exceeds a certain value, it'd restart, and use
> more sophisticated methods.
AFAICS this would be a net loss on average. Most of the time, the
constraint exclusion code doesn't win, and so throwing away all your
planning work to try it is going to be a loser most of the time.
regards, tom lane
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