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  • Definition
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New in version 5.3.

Configures balancer settings for a sharded collection, such as setting the chunk size for and defragmenting the collection.

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

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


This command is supported in all MongoDB Atlas clusters. For information on all commands, see Unsupported Commands.

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

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

The command has the following syntax:

configureCollectionBalancing: "<db>.<collection>",
chunkSize: <num>,
defragmentCollection: <bool>
enableAutoMerger: <bool>

configureCollectionBalancing has the following fields:

The name of the database and sharded collection to configure.
Sets the chunk size in MiB for the collection. The recommended size is 256, 512, or larger. For details on default behavior, see Default Behavior When chunkSize Is Not Specified.
Causes the balancer to defragment the collection. Defaults to false.
Whether or not the AutoMerger takes this collection into account. Defaults to true.

For more information, see Data Partitioning with Chunks.

To configure the chunk defragmentation throttling time parameter, see chunkDefragmentationThrottlingMS.

To learn about defragmenting sharded collections, see Defragment Sharded Collections.

If you do not specify chunkSize for a collection and no custom size has been set previously, the global default chunkSize is used for balancing.

If you use configureCollectionBalancing with chunkSize: 0, the per-collection chunkSize is reset and the global default chunkSize is used for balancing.

For more information on configuring default chunkSize, see Modify Range Size in a Sharded Cluster.

If you do not specify enableAutoMerger for a collection and no custom automerging behavior has been previously set, it defaults to true and will be taken into account by the AutoMerger.

To change the chunk size for a sharded collection, use the chunkSize option:

db.adminCommand( {
configureCollectionBalancing: "test.students",
chunkSize: 256
} )

Use this command to change the chunk size for the given collection.


By default, MongoDB cannot move a chunk if the number of documents in the chunk is greater than 2 times the result of dividing the configured chunk size by the average document size.

To find the average document size, see the avgObjSize field in the output of the db.collection.stats() method.

For more information, see Range Size.


We do not recommend using defragmentCollection to defragment sharded collections for MongoDB 6.0.0 to 6.0.3 and MongoDB 6.1.0 to 6.1.1, as the defragmentation process on these releases can make databases and collections unavailable for extended periods of time.

To tell the balancer to defragment a sharded collection, use the defragmentCollection option:

db.adminCommand( {
configureCollectionBalancing: "test.students",
defragmentCollection: true
} )

Use this command to have the balancer defragment a sharded collection. To monitor the chunk defragmentation process, use the balancerCollectionStatus command.

To learn more about defragmenting sharded collections, see Defragment Sharded Collections.

To defragment a sharded collection while updating the chunk size, use the defragmentCollection option and the chunkSize option together:

db.adminCommand( {
configureCollectionBalancing: "test.students",
chunkSize: 512,
defragmentCollection: true
} )

To explicitly disable the AutoMerger on a collection, set the enableAutoMerger option to false:

db.adminCommand( {
configureCollectionBalancing: "test.students",
enableAutoMerger: false
} )