shardCollection¶

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Definition
Considerations
Example
Additional Information

Definition¶

shardCollection¶

Enables a collection for sharding and allows MongoDB to begin distributing data among shards. You must run enableSharding on a database before running the shardCollection command. shardCollection has the following form:

{ shardCollection: "<database>.<collection>", key: <shardkey> }

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 index specification document to use as the shard key. The index must exist prior to the `shardCollection` command, unless the collection is empty. If the collection is empty, in which case MongoDB creates the index prior to sharding the collection. New in version 2.4: The key may be in the form `{ field : "hashed" }`, which will use the specified field as a hashed shard key.
`unique`	boolean	When `true`, the `unique` option ensures that the underlying index enforces a unique constraint. Hashed shard keys do not support unique constraints.
`numInitialChunks`	integer	Specifies the number of chunks to create initially when sharding an empty collection with a hashed shard key. MongoDB will then create and balance chunks across the cluster. The `numInitialChunks` must be less than `8192` per shard. If the collection is not empty, `numInitialChunks` has no effect.

Considerations¶

Use¶

Do not run more than one shardCollection command on the same collection at the same time.

MongoDB provides no method to deactivate sharding for a collection after calling shardCollection. Additionally, after shardCollection, you cannot change shard keys or modify the value of any field used in your shard key index.

Shard Keys¶

Choosing the best shard key to effectively distribute load among your shards requires some planning. Review Shard Keys regarding choosing a shard key.

Hashed Shard Keys¶

New in version 2.4.

Hashed shard keys use a hashed index of a single field as the shard key.

Note

If chunk migrations are in progress while creating a hashed shard key collection, the initial chunk distribution may be uneven until the balancer automatically balances the collection.

Example¶

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

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

Additional Information¶

Sharding, Sharding Concepts, and Deploy a Sharded Cluster.

← setShardVersion shardingState →

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