I tryed all you suggested me : (forme && '((...))'), drop the index and
recreate it and do a vacuum analyze and it
still do a sequential scan on the whole table.
> Ralf Mattes <rm@mh-freiburg.de> writes:
> > Still, the remarkl about running 'vacuum' after the creation
> > of an index seems valid. I was bitten by this just last week--
> > somehow it seems counterintuitive to have to vacuum a table only
> > to tell the system that an index exists. This should be the job
> > of 'create index' or am i wrong?
>
> The system knows perfectly well that the index exists. The issue
> is whether the planner will conclude that the index is worth using
> for a particular query, in the absence of complete statistical
> information. If you've never done a 'vacuum analyze' on the table
> then the planner is flying blind about what to do (and no, it does
> not matter whether the index exists at the time the vacuum is done).
>
> There are some subtle interactions between the default estimates that
> are made for various parameters. The current behavior clearly needs
> work, but I'm hesitant to "fix" it by just lowering the default
> selectivity estimate (or some such) without careful study.
>
> I'm hoping to have some time to spend on that issue for 7.2 ...
>
> regards, tom lane