db.collection.dropIndex()

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Definition

Behavior
Example

Definition

db.collection.dropIndex(index)

MongoDB with drivers

This page documents a mongosh method. To see the equivalent method in a MongoDB driver, see the corresponding page for your programming language:

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Drops or removes the specified index from a collection.

Note

You cannot drop the default index on the _id field.
You cannot specify db.collection.dropIndex("*") to drop all non-_id indexes. Use db.collection.dropIndexes() instead.

To get the index name or the index specification document for the db.collection.dropIndex() method, use the db.collection.getIndexes() method.

The db.collection.dropIndex() method takes the following parameter:

Parameter	Type	Description
`index`	string or document	Optional. Specifies the index to drop. You can specify the index either by the index name or by the index specification document. To drop a text index, specify the index name. You cannot specify `"*"` to drop all non-`_id` indexes. Use `db.collection.dropIndexes()` instead. If an index specified to `db.collection.dropIndex()` is still building, `db.collection.dropIndex()` attempts to stop the in-progress build. Stopping an index build has the same effect as dropping the built index. See Aborts In-Progress Index Builds for more complete documentation.

Behavior

The dropIndex() operation only kills queries that are using the index being dropped. This may include queries considering the index as part of query planning.

Resource Locking

db.collection.dropIndex() obtains an exclusive lock on the specified collection for the duration of the operation. All subsequent operations on the collection must wait until db.collection.dropIndex() releases the lock.

Aborts In-Progress Index Builds

New in version 4.4: If an index specified to db.collection.dropIndex() is still being built, dropIndex() attempts to abort the build. Aborting an index build has the same effect as dropping the built index. Prior to MongoDB 4.4, dropIndex() returned an error if the specified index was still building.

The index specified to dropIndex() must be the only index associated to the index builder, i.e. the indexes built by a single createIndexes or db.collection.createIndexes() operation. If the associated index builder has other in-progress builds, wait until the builds complete and specify the index to dropIndex().

For example, a createIndexes / createIndexes() operation creates three indexes. Assuming all three index builds are still in-progress, dropIndex() cannot successfully abort any of the index builds and therefore cannot drop any of those indexes.

Use currentOp to identify the index builds associated to a createIndexes / createIndexes() operation. See Active Indexing Operations for an example.

For replica sets or shard replica sets, aborting an index on the primary does not simultaneously abort secondary index builds. dropIndex() attempts to abort the in-progress builds for the specified indexes on the primary and if successful creates an associated "abort" oplog entry. Secondary members with replicated in-progress builds wait for a commit or abort oplog entry from the primary before either committing or aborting the index build.

Hidden Indexes

MongoDB offers the ability to hide or unhide indexes from the query planner. By hiding an index from the planner, you can evaluate the potential impact of dropping an index without actually dropping the index.

If after the evaluation, the user decides to drop the index, you can drop the hidden index; i.e. you do not need to unhide it first to drop it.

If, however, the impact is negative, the user can unhide the index instead of having to recreate a dropped index. And because indexes are fully maintained while hidden, the indexes are immediately available for use once unhidden.

For more information on hidden indexes, see Hidden Indexes.

Example

Consider a pets collection. Calling the getIndexes() method on the pets collection returns the following indexes:

[
   {
      "v" : 2,
      "key" : {
         "_id" : 1
      },
      "name" : "_id_"
   },
   {
      "v" : 2,
      "key" : {
         "cat" : -1
      },
      "name" : "catIdx"
   },
   {
      "v" : 2,
      "key" : {
         "cat" : 1,
         "dog" : -1
      },
      "name" : "cat_1_dog_-1"
   }
]

The single field index on the field cat has the user-specified name of catIdx [1] and the index specification document of { "cat" : -1 }.

To drop the index catIdx, you can use either the index name:

db.pets.dropIndex( "catIdx" )

Or you can use the index specification document { "cat" : -1 }:

db.pets.dropIndex( { "cat" : -1 } )

[1]	During index creation, if the user does not specify an index name, the system generates the name by concatenating the index key field and value with an underscore, e.g. `cat_1`.

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