shardCollection

Definition

shardCollection

Shards a collection to distribute its documents across shards. You must run enableSharding on a database before running the shardCollection command. The shardCollection command must be run against the admin database.

To run shardCollection, use the db.runCommand( { <command> } ) method.

Tip

In the mongo Shell, this command can also be run through the sh.shardCollection() helper method.

Helper methods are convenient for mongo 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.

shardCollection has the following form:

{
   shardCollection: "<database>.<collection>",
   key: { <field1>: <1|"hashed">, ... },
   unique: <boolean>,
   numInitialChunks: <integer>,
   presplitHashedZones: <boolean>,
   collation: { locale: "simple" }
}

shardCollection has the following fields:

Field	Type	Description
shardCollection	string	The namespace of the collection to shard in the form <database>.<collection>.
key	document	The document that specifies the field or fields to use as the shard key. { <field1>: <1|"hashed">, ... } Set the field values to either: 1 for ranged based sharding "hashed" to specify a hashed shard key. shard key must be supported by an index. Unless the collection is empty, the index must exist prior to the shardCollection command. If the collection is empty, MongoDB creates the index prior to sharding the collection if the index that can support the shard key does not already exist. See also Shard Key Indexes
unique	boolean	Specify true to ensure that the underlying index enforces a unique constraint. Defaults to false. You cannot specify true when using hashed shard keys.
numInitialChunks	integer	Specifies the initial number of chunks to create across all shards in the cluster when sharding an empty collection with a hashed shard key. MongoDB will then create and balance chunks across the cluster. The numInitialChunks must result in less than 8192 per shard. If the collection is not empty or the shard key does not contain a hashed field, the operation returns an error. If sharding with presplitHashedZones: true, MongoDB attempts to evenly distribute the specified number of chunks across the zones in the cluster. If sharding with presplitHashedZones: false or omitted and no zones and zone ranges are defined for the empty collection, MongoDB attempts to evenly distributed the specified number of chunks across the shards in the cluster. If sharding with presplitHashedZones: false or omitted and zones and zone ranges have been defined for the empty collection, numInitChunks has no effect. Changed in version 4.4.
collation	document	Optional. If the collection specified to shardCollection has a default collation, you must include a collation document with { locale : "simple" }, or the shardCollection command fails. At least one of the indexes whose fields support the shard key pattern must have the simple collation.
presplitHashedZones	boolean	Optional. Specify true to perform initial chunk creation and distribution for an empty or non-existing collection based on the defined zones and zone ranges for the collection. For hashed sharding only. shardCollection with presplitHashedZones: true returns an error if any of the following are true: The shard key does not contain a hashed field (i.e. is not a single field hashed index or compound hashed index). The collection has no defined zones or zone ranges. The defined zone range or ranges do not meet the requirements. New in version 4.4.

Considerations

Example

The following operation enables sharding for the people collection in the records database and uses the zipcode field as the shard key:

db.adminCommand( { shardCollection: "records.people", key: { zipcode: 1 } } )