We're running a huge MongoDB with a large index (made of of four fields) which was created ad-hoc and should now be superseded by slimmer one (of the first two fields). But the problem is we can't just delete the old one as the warmup of the new one may take hours (or days!). We have two secondary instances, is it possible to only delete the large index on one of those and have that instance take over when the new index is warmed? Or is there some way to guide Mongo to the new indices?
Edit: on a small test database Mongo rejects the new index after I delete the old one and instead uses half of third index, even though the new one is a perfect fit for the query. How to guide/update the query plan?