moveChunk (database command)

Definition

moveChunk

Internal administrative command. Moves chunks between shards. Issue the moveChunk command via a mongos instance while using the admin database. Use the following forms:

Tip

In mongosh, this command can also be run through the sh.moveChunk() helper method.

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.

db.adminCommand( { moveChunk : <namespace> ,
                 find : <query> ,
                 to : <string>,
                 forceJumbo: <boolean>,
                 _secondaryThrottle : <boolean>,
                 writeConcern: <document>,
                 _waitForDelete : <boolean> } )

Alternatively:

db.adminCommand( { moveChunk : <namespace> ,
                 bounds : <array> ,
                 to : <string>,
                 forceJumbo: <boolean>,
                 _secondaryThrottle : <boolean>,
                 writeConcern: <document>,
                 _waitForDelete : <boolean> } )

The moveChunk command has the following fields:

Field	Type	Description
moveChunk	string	The namespace of the collection where the chunk exists. Specify the collection's full namespace, including the database name.
find	document	An equality match on the shard key that specifies the shard-key value of the chunk to move. Specify either the bounds field or the find field but not both. Do not use the find field to select chunks in collections that use a hashed shard key.
bounds	array	The bounds of a specific chunk to move. The array must consist of two documents that specify the lower and upper shard key values of a chunk to move. Specify either the bounds field or the find field but not both. Use bounds to select chunks in collections that use a hashed shard key.
to	string	The name of the destination shard for the chunk.
forceJumbo	boolean	Optional. A flag that determines if the command can move a chunk that is too large to migrate. The chunk may or may not be labeled as jumbo. If true, the command can move the chunk. If false, the command cannot move the chunk. The default is false. WARNING: The moveChunk command with forceJumbo=true blocks write operations on the collection. This option causes the shard to migrate chunks even when they are larger than the configured chunk size. The collection remains unavailable for writes for the duration of the migration. To migrate these large chunks without this long blocking period, see Balance Ranges that Exceed Size Limit instead.
_secondaryThrottle	boolean	Optional. For WiredTiger, defaults to false. If true, then by default, each document move during chunk migration propagates to at least one secondary before the balancer proceeds with the next document. This is equivalent to a write concern of { w: 2 }. Use the writeConcern option to specify a different write concern. If false, the balancer does not wait for replication to a secondary and instead continues with the next document. For more information, see Secondary Throttle.
writeConcern	document	Optional. A document that expresses the write concern that the _secondaryThrottle will use to wait for secondaries during the chunk migration. writeConcern requires _secondaryThrottle: true.
_waitForDelete	boolean	Optional. If set to true, the delete phase of a moveChunk operation is blocking. _waitForDelete defaults to false. When the _waitForDelete field is set, MongoDB does not wait on the orphanCleanupDelaySecs delay before performing the range deletion. If you use the _waitForDelete parameter and have any read operations occurring on secondaries, the read may miss documents due to the migration's delete phase.

The value of bounds takes the form:

[ { hashedField : <minValue> } ,
  { hashedField : <maxValue> } ]

The chunk migration section describes how chunks move between shards on MongoDB.

Compatibility

This command is available in deployments hosted in the following environments:

• MongoDB Atlas: The fully managed service for MongoDB deployments in the cloud

• MongoDB Enterprise: The subscription-based, self-managed version of MongoDB

• MongoDB Community: The source-available, free-to-use, and self-managed version of MongoDB

Considerations

Only use the moveChunk in special circumstances such as preparing your sharded cluster for an initial ingestion of data, or a large bulk import operation. In most cases allow the balancer to create and balance chunks in sharded clusters. See Create Ranges in a Sharded Cluster for more information.

Behavior

errmsg: "The collection's metadata lock is already taken."