Paul <paul(at)wayr(dot)org> writes:
> Why in the first case, pgsql uses the "better" index and if i search
> r_service instead of r_numero pgsql does a "Bitmap Heap scan" first ?
Given the difference in the number of rows to be fetched, both plan
choices look pretty reasonable to me. If you want to experiment,
you can try forcing the other choice in each case (use enable_indexscan
and enable_bitmapscan) and see how fast it is, but I suspect the planner
got it right.
Beware of cache effects when trying two plans in quick succession ---
the second one might go faster just because all the data is already
swapped in.
regards, tom lane