balancerStart

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Definition

Compatibility
Syntax
Example

Definition

balancerStart

Starts the balancer thread. The command does not wait for a balancing round to start.

Tip

In mongosh, this command can also be run through the sh.startBalancer() 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.

Starting in MongoDB 6.0.3, automatic chunk splitting is not performed. This is because of balancing policy improvements. Auto-splitting commands still exist, but do not perform an operation. For details, see Balancing Policy Changes.

In MongoDB versions earlier than 6.0, the command enables auto-splitting for the sharded cluster. To disable auto-splitting when the balancer is enabled, you can use sh.disableAutoSplit().

Compatibility

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

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

Important

This command is not supported in serverless instances. For more information, 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

You can only issue the balancerStart against the admin database on a mongos instance.

The command has the following syntax:

db.adminCommand(
   {
     balancerStart: 1,
     maxTimeMS: <number>
   }
)

Command Fields

Field	Type	Description
`balancerStart`	any	Any value.
`maxTimeMS`	integer	Optional. Time limit for enabling the balancer. Defaults to 60000 milliseconds.

Example

To start the balancer thread, connect to a mongos instance and issue the following command:

db.adminCommand( { balancerStart: 1 } )