From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-patches(at)postgresql(dot)org |
Subject: | Re: Constraint Exclusion (Partitioning) - Initial Review |
Date: | 2005-07-04 04:16:12 |
Message-ID: | 23470.1120450572@sss.pgh.pa.us |
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Lists: | pgsql-hackers pgsql-patches |
Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> Simon Riggs wrote:
>>> Oh, why would someone want to set enable_constraint_exclusion to false?
>>
>> The included functionality performs the exclusion at plan time. If a
>> query was prepared for later execution, it *could* return the wrong
>> answer when the plan was executed at a later time since plans are not
>> invalidated when constraints change. So, in general, this should be set
>> to false except for circumstances where the user can guarantee no such
>> mistake would be made.
> Ah, so there is a small additional restriction (changing constraints on
> planned queries) that this would affect.
This is a stopgap until we have automatic plan invalidation.
regards, tom lane
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