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Sharding

configureCollectionBalancing

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  • Definition
  • Compatibility
  • Syntax
  • Behavior
  • Examples

Definition

configureCollectionBalancing

New in version 5.3.

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

Compatibility

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

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

Note

This command is supported in all MongoDB Atlas clusters. For information on Atlas support for 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

Syntax

The command has the following syntax:

db.adminCommand(
   {
     configureCollectionBalancing: "<db>.<collection>",
     chunkSize: <num>,
     defragmentCollection: <bool>
   }
)

Command Fields

configureCollectionBalancing has the following fields:

Field
Type
Description
configureCollectionBalancing
string
Required: The name of the database and sharded collection to configure.
chunkSize
integer
Optional: Sets the chunk size in MiB for the collection. The recommended size is 256, 512, or larger.
defragmentCollection
boolean
Optional: Causes the balancer to defragment the collection.

For more information, see Data Partitioning with Chunks.

Behavior

No Collection chunkSize Specified

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.

Specifying chunkSize: 0

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.

Examples

Configure Chunk Size

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.

Warning

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.

Defragment Collections

Warning

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.

Reconfigure and Defragment 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
} )

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