dropIndexes¶

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~~Behavior~~行为
~~Examples~~示例

dropIndexes¶

The dropIndexes command drops one or more indexes (except the index on the _id field) from the specified collection.

The command has the following form:

{ dropIndexes: <string>, index: <string|document|arrayofstrings>, writeConcern: <document>, comment: <any> }

The command takes the following fields:

~~Field~~字段	~~Type~~类型	~~Description~~描述
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 but the _id index from the collection, 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. To drop multiple indexes (Available starting in MongoDB 4.2), specify an array of the index names.
writeConcern	document	~~Optional.~~可选。A document expressing the write concern of the `drop` command. Omit to use the default write concern.
`comment`	any	~~Optional.~~可选。A user-provided comment to attach to this command. Once set, this comment appears alongside records of this command in the following locations: mongod log messages, in the `attr.command.cursor.comment` field. Database profiler output, in the `command.comment` field. `currentOp` output, in the `command.comment` field. A comment can be any valid BSON type (string, integer, object, array, etc). ~~New in version 4.4.~~版本4.4中的新功能。

Behavior行为¶

Resource Locking¶

~~Changed in version 4.2.~~在版本4.2中更改。

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.

Abort In-Progress Index Builds¶

New in version 4.4:If an index specified to dropIndexes is still building, dropIndexes attempts to abort the in-progress build. Aborting an index build has the same effect as dropping the built index. Prior to MongoDB 4.4, dropIndexes would return an error if the collection had any in-progress index builds.

For replica sets, run dropIndexes on the primary. The primary aborts the index build and creates an associated “abortIndexBuild” oplog entry. Secondaries which replicate the “abortIndexBuild” oplog entry abort the in-progress index build and discard the build job. See Index Build Process for detailed documentation on the index build process and the specific timing for terminating an in-progress index build.

The indexes specified to dropIndexes must be the entire set of in-progress builds associated to a single createIndexes or db.collection.createIndexes() operation. To drop a specific index out of a set of related in-progress builds, wait until the index builds complete and specify that index to dropIndexes.

For example, a createIndexes / createIndexes() operation creates three indexes. Assuming all three index builds are in-progress, dropIndexes must specify all three indexes to abort the index builds.

Use currentOp to identify the index builds associated to a createIndexes / 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示例¶

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" })
```
The mongo shell 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" ] } )

dropIndexes¶

Behavior行为¶

Kill related queries only¶

Resource Locking¶

Index Names¶

_id Index¶

text Indexes¶

Abort In-Progress Index Builds¶

Hidden Indexes¶

Examples示例¶

`_id` Index¶