The type int8 and the use of indexes

   Hi,

   I realized that PostgreSQL (7.0.3) optimizer doesn´t use indexes in a query
like "select * from my table where pk=1", where the field pk is of  type int8.
I changed the type to int4, and now it uses the index (a lot faster). I also
tryed changing the type to numeric, with the same results.
   Why does it happen? Is there something special with type int8 ???


                                       Thanks,
                                            Nelson