We've a collection with two fields ( A and B ), both have an index.

Getting the disctinct on any of them is amazingly quick. But the actual query is a disctinct in A with a filter on the other field, B.

```
db.getCollection('Collection').distinct( "A" , { "B" : "b1" }  )

```

This is really, really slow as it's scanning the collection ( unfortunatly b1 is not filtering more than a 50% ). Is there a way to make this quicker in MongoDB ?