> explain select event_id from history where event_type = 120;
> NOTICE: QUERY PLAN:
>
> Seq Scan on history (cost=0.00..446079.00 rows=200000 width=8)
>
> even if I do a drop index history_idx, explains sais the same.
>
Try
explain select event_id from history where event_type = 120::int8;
See
http://fts.postgresql.org/db/mw/msg.html?mid=1031765
for some further explanation/history.
HTH,
-- Joe