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dropIndexes

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  • Definition
  • Syntax
  • Command Fields
  • Behavior
  • Examples

Definition

dropIndexes

Changed in version 6.0.

The dropIndexes command drops one or more indexes (except the index on the _id field and the last remaining shard key index, if one exists) from the specified collection.

Tip

In mongosh, this command can also be run through the db.collection.dropIndex() and db.collection.dropIndexes() helper methods..

Helper methods are convenient for mongosh users, but they may not return the same level of information as database commands. In cases where the convenience is not needed or the additional return fields are required, use the database command.

Syntax

The command has the following syntax:

db.runCommand(
   {
     dropIndexes: <string>,
     index: <string|document|arrayofstrings>,
     writeConcern: <document>, comment: <any>
   }
)

Command Fields

The command takes the following fields:

Field
Type
Description
dropIndexes
String
The name of the collection whose indexes to drop.
index
string or document or array of strings

The index or indexes to drop.

  • To drop all indexes except the _id index and the last remaining shard key index from the collection if one exists, specify "*".

  • To drop a single index, specify either the index name, the index specification document (unless the index is a text index), or an array of the index name. To drop a text index, specify the index names instead of the index specification document. If this index is the last remaining shard key index, dropIndexes raises an error.

  • To drop multiple indexes (Available starting in MongoDB 4.2), specify an array of the index names.

writeConcern
document
Optional. A document expressing the write concern of the drop command. Omit to use the default write concern.
comment
any

Optional. A user-provided comment to attach to this command. Once set, this comment appears alongside records of this command in the following locations:

A comment can be any valid BSON type (string, integer, object, array, etc).

New in version 4.4.

Behavior

Starting in MongoDB 6.0, dropIndexes raises an error if you attempt to use it to remove the last remaining shard key compatible index. Passing "*" to dropIndexes drops all indexes except the _id index and the last remaining shard key compatible index, if one exists.

Starting in MongoDB 5.2, you can use dropIndexes to drop existing indexes on the same collection even if there is a build in progress on another index. In earlier versions, attempting to drop a different index during an in-progress index build results in a BackgroundOperationInProgressForNamespace error.

Kill related queries only

Starting in MongoDB 4.2, the dropIndexes operation only kills queries that are using the index being dropped. This may include queries considering the index as part of query planning.

Prior to MongoDB 4.2, dropping an index on a collection would kill all open queries on the collection.

Resource Locking

Changed in version 4.2.

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

Prior to MongoDB 4.2, dropIndexes obtained an exclusive lock on the parent database, blocking all operations on the database and all its collections until the operation completed.

Index Names

If the method is passed an array of index names that includes a non-existent index, the method errors without dropping any of the specified indexes.

_id Index

You cannot drop the default index on the _id field.

text Indexes

To drop a text index, specify the index name instead of the index specification document.

Stop In-Progress Index Builds

Starting in MongoDB 4.4, if an index specified to dropIndexes is still building, dropIndexes attempts to stop the in-progress build. Stopping an index build has the same effect as dropping the built index. In versions earlier than MongoDB 4.4, dropIndexes returns an error if there are any index builds in progress on the collection.

For replica sets, run dropIndexes on the primary. The primary stops the index build and creates an associated "abortIndexBuild" oplog entry. Secondaries which replicate the "abortIndexBuild" oplog entry stop the in-progress index build and discard the build job. See Index Build Process for detailed documentation on the index build process.

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

Hidden Indexes

Starting in version 4.4, MongoDB adds the ability to hide or unhide indexes from the query planner. By hiding an index from the planner, users 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, the user 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.

Examples

  • To drop all non-_id indexes , specify "*" for the index (See Indexes Named *).

    db.runCommand( { dropIndexes: "collection", index: "*" } )

  • To drop a single index, issue the command by specifying the name of the index you want to drop. For example, to drop the index named age_1, use the following command:

    db.runCommand( { dropIndexes: "collection", index: "age_1" })

    mongosh provides the helper methods db.collection.dropIndex() and db.collection.dropIndexes():

    db.collection.dropIndex("age_1");

  • To drop multiple indexes, issue the command by specifying an array of the index names:

    db.runCommand( { dropIndexes: "collection", index: [ "age_1", "age_1_status_1" ] } )

Tip

See also:

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