От: Marc Cousin
Тема: Re: Weird row estimate
Дата: ,
Msg-id: 200707121055.08230.mcousin@sigma.fr
(см: обсуждение, исходный текст)
Ответ на: Re: Weird row estimate  (Tom Lane)
Список: pgsql-performance

Le Wednesday 11 July 2007 22:35:31 Tom Lane, vous avez écrit :
> Marc Cousin <> writes:
> > Nevertheless, shouldn't the third estimate be smaller or equal to the sum
> > of the two others ?
>
> The planner's estimation for subplan conditions is pretty primitive
> compared to joinable conditions.  When you add the OR, it's no longer
> possible to treat the IN like a join, and everything gets an order of
> magnitude dumber :-(
>
> It might be worth trying this as a UNION of the two simple queries.

Yes, it's much better on this query with a UNION.
The problem is that this is a small set of the query, and there are several
nested IN with an OR condition... But at least now I understand where it
comes from.
Thanks a lot.


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