MongoDB versions prior to 2.0, however, support only the {v:0} format. If you need to roll back MongoDB to a version prior to 2.0, you must drop and re-create your indexes. 

To build pre-2.0 indexes, use the dropIndexes() and createIndex() methods. You cannot simply reindex the collection. When you reindex on versions that only support {v:0} indexes, the v fields in the index definition still hold values of 1 , even though the indexes would now use the {v:0} format. If you were to upgrade again to version 2.0 or later, these indexes would not work. 

## Example 

Suppose you rolled back from MongoDB 2.0 to MongoDB 1.8, and suppose you had the following index on the items collection: 

{ "v" : 1, "key" : { "name" : 1 }, "ns" : "mydb.items", "name" : "name_1" } 

The v field tells you the index is a {v:1} index, which is incompatible with version 1.8. To drop the index, issue the following command: 

db.items.dropIndex( { name : 1 } ) 

To recreate the index as a {v:0} index, issue the following command: 

db.foo.createIndex( { name : 1 } , { v : 0 } ) 

## See also: 

Index Performance Enhancements (page 910). 

## 8.3.2 Index Management Tutorials 

Instructions for managing indexes and assessing index performance and use. 

Remove Indexes (page 524) Drop an index from a collection. 

Modify an Index (page 525) Modify an existing index. 

Rebuild Indexes (page 526) In a single operation, drop all indexes on a collection and then rebuild them. 

Manage In-Progress Index Creation (page 527) Check the status of indexing progress, or terminate an ongoing in- dex build. 

Return a List of All Indexes (page 527) Obtain a list of all indexes on a collection or of all indexes on all collections in a database. 

Measure Index Use (page 528) Study query operations and observe index use for your database. 

## Remove Indexes 

To remove an index from a collection use the dropIndex() method and the following procedure. If you simply need to rebuild indexes you can use the process described in the Rebuild Indexes (page 526) document. 

## See also: 

Indexing Tutorials (page 517) and Index Concepts (page 486) for more information about indexes and indexing oper- ations in MongoDB. 

