Slide 79
Slide 79 text
Limited Indexes
1. Given a compound index on [a, b]
2. {a: 1, b: 2} and {$and: [{a: 1}, {b: 2}]} are equivalent
3. Only the former picks up the compound index
4. Negations never use indexes
5. {$or: […]} is implemented as two parallel queries,
both clauses might need separate indexes.