performance - Does field type matter in a MongoDB index?

Question

Here are two examples of a document structure in MongoDB.

{  
 UserId: "123",  
 UserName: "Usain Bolt"  
}



{  
 UserId: NumberLong(123),  
 UserName: "Usain Bolt"  
}

If I were to create an index on UserID, would there be a difference in find query performance between the above two examples?

Answer 1

I don't have a specifically accurate answer on the matter, but here is my understanding:

Indexes

Indexed fields may be of any type, including (embedded) documents

Indexes are mostly likely hashed, regardless of the type, to be able to index the same way. If there were specific considerations to be observed for different types, the standard mongodb docs would make that distinction.

The answer given to a similar question here refers to code samples from mongodb, that suggests the index comparisons are pretty much the same regarding types, but probably performance geared towards the size of the index.