| From: | Gregory Stark <stark(at)enterprisedb(dot)com> |
|---|---|
| To: | "Jim Nasby" <decibel(at)decibel(dot)org> |
| Cc: | "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, <pgsql-hackers(at)postgreSQL(dot)org> |
| Subject: | Re: Effects of GUC settings on automatic replans |
| Date: | 2007-03-25 00:06:58 |
| Message-ID: | 871wje4259.fsf@oxford.xeocode.com |
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| Lists: | pgsql-hackers |
"Jim Nasby" <decibel(at)decibel(dot)org> writes:
> On Mar 21, 2007, at 5:11 AM, Tom Lane wrote:
>> constraint_exclusion
>>
>> I'm inclined not to worry about these, since changing them can't affect
>> the semantics of the query, at worst its performance.
>
> Hrm... wasn't that option added in case there was a bug in the exclusion code?
> I certainly can't think of any performance reason why you'd want to disable
> it... so it might be worth invalidating plans if it changes.
It was added precisely because we didn't have plan invalidation... If you
dropped a constraint there was previously nothing to force the plan to be
recalculated if it depended on the constraint for correctness.
--
Gregory Stark
EnterpriseDB http://www.enterprisedb.com
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