Why is mongodb slow when searching?

Question

MongoDB

There is a collection, it has a little more than 21 million documents, some documents have a field: true, the rest do not have this field at all.
db.collection.find({"field": {$ne: true}}).count()
It always takes from 14 seconds, such documents are 18.5KK. An index on this field has been created, in total, documents in this collection have 4 fields, indexes for each.
Is there any way to increase the speed?

Answer 1

indexes on true/false are not effective in any bases, it is easier to transfer them to a separate collection.
it is quite possible that the search does not go by the index (but a full enumeration), for the index you need to fill in the field and search for false.
You can also try $exists: false