[wulczer]

There are cases where a full table scan is faster than an index scan, and there are cases where the index scan is faster. There are even cases where the only option is a full table scan!

I still don't see what a setting that gives errors when a particular access method has been chosen would be good for.

You don't care about the plan, you care about how fast the query runs.

You'll always have to do reactive development when trying to get good performance. There is only so much simulating and testing you can do and real data volume and distribution changes all the time.