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Sharding

addShard

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  • Definition
  • Compatibility
  • Syntax
  • Considerations
  • Examples

Definition

addShard

Adds a shard replica set to a sharded cluster.

Tip

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

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.

Syntax

The command has the following syntax:

db.adminCommand(
   {
     addShard: "<replica_set>/<hostname><:port>",
     name: "<shard_name>"
   }
)

Command Fields

Note

Starting in version 6.2, MongoDB removes the maxSize field from the addShard command. As a result:

  • Running addShard with the maxSize field returns an InvalidOptions error.

  • New documents in the shards collection no longer include the maxSize field.

  • Any pre-existing maxSize field entries are ignored.

The command contains the following fields:

Field
Type
Description

addShard

string

The replica set name, hostname, and port of at least one member of the shard's replica set. Any additional replica set member hostnames must be comma separated. For example:

<replica_set>/<hostname><:port>,<hostname><:port>, ...

name

string

Optional. A name for the shard. If this is not specified, MongoDB automatically provides a unique name.

The addShard command stores shard configuration information in the config database. Always run addShard when using the admin database.

Considerations

Balancing

When you add a shard to a sharded cluster, you affect the balance of chunks among the shards of a cluster for all existing sharded collections. The balancer will begin migrating chunks so that the cluster will achieve balance. See Balancer Internals for more information.

Hidden Members

Important

You cannot include a hidden member in the seed list provided to addShard.

DDL Operations

If you add a shard while your cluster executes a DDL operation (operation that modifies a collection such as reshardCollection), addShard only executes after the concurrent DDL operation finishes.

Examples

The following command adds a replica set as a shard:

use admin
db.runCommand( { addShard: "repl0/mongodb3.example.net:27327"} )

Warning

Do not use localhost for the hostname unless your config server is also running on localhost.

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