Do I need composite indices if each attribute is indexed in mongodb collection?

Question

Suppose I have a collection in a mongo database with the following documents

{
    "name" : "abc",
    "email": "abc@xyz.com",
    "phone" : "+91 1234567890"
}

The collection has a lot of objects (a million or so), and my application, apart from regularly adding objects to this collection, does a few different types of finds on this data.

One method does a find with all the three attributes (name, email and phone), so I can make a composite index for those three fields to make sure this find works effiently.

db.mycollection.ensureIndex({name:1,email:1,phone:1})

Now, I also have methods in my application which fetch all the objects with the same name (bad example, I know). So I need an index for the name field.

db.mycollection.ensureIndex({name:1})

Gradually, my application grows to a point where I have to index the other fields.

Now, my question. If I have each of the attributes indexed individually, does it still make sense to maintain composite indices for all three attributes (or 2 of the attributes)?

Obviously, this is a bad example... If I were making a collection to store multiple contact info for a person, I'd use arrays. But, this question is purely about the indexes.

Answer 1

Just to answer my own question for sake of completion:
Compound indexes don't mean that each of the individual attributes are indexed, only the first attribute in the compound index can be used alone in a find with efficiency. The idea is to strike a balance and optimize queries, as too many indexes increase disk storage and insertion time.

Answer 2

It depends on your queries.

If you are doing a query such as:

db.mycollection.find({"name": "abc", email: "abc@xyz.com", phone: "+91 1234567890"});

then a composite index would be the most efficient.