Re: empty string causes planner to avoid index. Makes me sad.

Le vendredi 27 novembre 2009 à 23:32:14, Jeff Amiel a écrit :
> --- On Fri, 11/27/09, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > You didn't show us any evidence of that, either. Both
> > of your test
> > cases are using the index.
>
> Ok...third try. The cost when passing in an empty string is SIGNIFICANTLY
> higher than when not. Wouldn't seem that the planner is using the index
> effectively.
>
> Aggregate (cost=231884.57..231884.57 rows=1 width=0)
>
> versus
>
> Aggregate (cost=34.83..34.83 rows=1 width=0)
>

But in the first example (the empty string one), it fetched 170468 rows from
the index, and in the second one (the 17-spaces string), it fetched only 18
rows. It seems quite normal that the first one is costier then the second one.

--
Guillaume.
http://www.postgresqlfr.org
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