I got burned by this recently and found the answer on the net:
When selecting on a column with an INT8 index, alway put
quotes around the constant value:
select * from a where id = '6970';
Otherwise the constant is assumed to be an INT4, which doesn't match the
type in the index, so the index is not used.
> of course i vacuum'ed, but when i select anything from the table i get
> seqscan:
> depesz=# explain select * from a where id = 6970;
> NOTICE: QUERY PLAN:
>
> Seq Scan on a (cost=0.00..465.76 rows=1 width=8)
>
> EXPLAIN
>
> what could be possible reason?
>
