mongodb indexes?

Question

MongoDB

What indexes should be for such a query?

db.foo.find({
        $or : [ { a : 1 } , { b : 2 } ],
        c: {$lte: 3}
    }).sort( { c : -1 } )

I tried to test it, but I don't see an unambiguous dependence of speed on indexing for individual fields or for all together. Whether have in general sense indexes on many fields. Thank you!

Answer 1

> Whether indexes on many fields
have in general sense, if only on these fields there is a search. Example db.user.find({city:'Moscow', sex:0, age:18})
building a composite index on the fields city,sex,age

Answer 2

Definitely need db.foo.ensureIndex({c:1})
Then create a large test set and use explain.