Compatibility and Index Type Changes in MongoDB 2.4

New Index Types

In 2.4 MongoDB adds two new index types: 2dsphere and text. These index types do not exist in 2.2, and for each database, creating a 2dsphere or text index, will upgrade the data-file version and make that database incompatible with 2.2.

If you intend to downgrade, you should always drop all 2dsphere and text indexes before moving to 2.2.

You can use the downgrade procedure to downgrade these databases and run 2.2 if needed, however this will run a full database repair (as with repairDatabase) for all affected databases.

Index Type Validation

In MongoDB 2.2 and earlier you could specify invalid index types that did not exist. In these situations, MongoDB would create an ascending (e.g. 1) index. Invalid indexes include index types specified by strings that do not refer to an existing index type, and all numbers other than 1 and -1. [1]

In 2.4, creating any invalid index will result in an error. Furthermore, you cannot create a 2dsphere or text index on a collection if its containing database has any invalid index types. [1]

db.coll.ensureIndex( { field: "1" } )

{
  "err" : "Unknown index plugin '1' in index { field: \"1\" }"
  "code": 16734,
  "n": <number>,
  "connectionId": <number>,
  "ok": 1
}