rihad <rihad(at)mail(dot)ru> writes:
> You mean Postgres wouldn't *always* use created_at's index with such
> access patterns on a big table (even if one exists):
> select * from foo order by created_at desc;
No, it wouldn't necessarily, and that's a good thing. A full-table
indexscan can often be slower than a sort because of inefficient disk
access patterns. The planner will estimate the cost of each possibility
and pick the one that looks cheaper.
regards, tom lane