Question

Is tip #25 in Tips and Tricks for MongoDB Developers correct?

It says that this query:

collection.find({"x" : criteria, "y" : criteria, "z" : criteria})

can be optimized with

collection.ensureIndex({"y" : 1, "z" : 1, "x" : 1})

I think it’s false because for this to work, x should be in front. I thought the order of indexes matter.

So where did I go wrong?

Answer 1

The order of the fields in the index only matters if the query doesn’t include all of the fields in the index. This query is referencing all three fields so the order of the fields in the index doesn’t matter.

See more details in the docs on compound indexes.

The order of the fields in the find query object is not relevant.