@Kushagra_Kesav There’s another case I would like to discuss for the same collection.
I have a query like following
db.someCollection.find({someKey: {$exists: false},someId:{$in:[<260 objectids>] }}).sort({_id:1})
If I apply index on > {someKey:1, someId:1, _id:1} and run the above query with 180 objectids the index is applied. But if I run the above query as is on 260 objectids, the it does the IXSCAN but on _id. Not sure what is the issue ?
Seems like fields with $exists : false do not accept indexes
The other finding is that if I only apply index on { someId:1, _id:1} the query still uses IXSCAN on _id whereas i believe it should use IXSCAN on { someId:1, _id:1}.
Please help