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Re: Effects of GUC settings on automatic replans

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 (view raw or flat)
Thread:
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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