Richard Neill <rn214(at)richardneill(dot)org> writes:
> Also, I wonder whether it matters which order the indexes are created in?
IIRC, if the estimated costs of using two different indexes come out the
same (to within 1% or so), then the planner keeps the first-generated
path, which will result in preferring the index with smaller OID. This
effect doesn't apply to your problem query though, since we can see from
the drop-experiments that the estimated costs are quite a bit different.
A more likely explanation if you see some effect that looks like order
dependency is that the more recently created index has accumulated less
bloat, and thus has a perfectly justifiable cost advantage.
regards, tom lane