With the new btree skipping implementation, currently nscanned counts the number of documents which match the query according to the index spec. But this can result in situations in which indexes which require skipping have the same nscanned as indexes not requiring skipping.

One solution is to include in nscanned the number of btree entries touched during skipping. Currently there's no way to transfer that information from the btree implementation to the query optimizer, but that can be added.

I can implement, but sounds like a good idea Eliot?