"Jim Nasby" <[EMAIL PROTECTED]> 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

---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
       choose an index scan if your joining column's datatypes do not

Reply via email to