Re: Appending "LIMIT" to query drastically decreases performance

In response to Matthew <matthew(at)flymine(dot)org>:

> On Fri, 30 Nov 2007, cluster wrote:
> > Can anyone explain the following odd behavior?
> > I have a query that completes in about 90 ms. If I append LIMIT to the
> > very end, eg. "LIMIT 500" the evaluation time increases to about 800 ms.
> > How can performance get *worse* by giving the database the option to
> > stop the evaluation earlier (when it reaches the output 500 rows)?
>
> The planner doesn't always get it right. Simple.
>
> Have you done a "VACUUM FULL ANALYSE" recently?

I don't know about the "FULL" part ... but certainly an ANALYZE.

Please post EXPLAIN ANALYZE output for the two queries.

--
Bill Moran
Collaborative Fusion Inc.
http://people.collaborativefusion.com/~wmoran/

wmoran(at)collaborativefusion(dot)com
Phone: 412-422-3463x4023

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