frbn(at)efbs-seafrigo(dot)fr writes:
> on a +10 millions rec table, a simple select:
> SELECT * FROM tab where num = x;
> time: 5 secondes
> SELECT * FROM tab WHERE num = x OR num = y;
> time: more than 10 mn !!!
What does EXPLAIN show? Have you VACUUM ANALYZEd the table recently
(or indeed ever)? This looks a lot like the behavior on a
never-vacuumed table --- the default statistical assumptions are such
that an indexscan looks like a win for one equality clause, but not
for two ORed clauses.
regards, tom lane