Refine a Shard Key优化分片关键点

New in version 4.4.在版本4.4中新增。

Refining a collection's shard key allows for a more fine-grained data distribution and can address situations where the existing key has led to jumbo chunks due to insufficient cardinality.优化集合的分片键可以实现更细粒度的数据分发，并且可以解决现有键由于基数不足而导致大块的情况。

Note注意

Starting in MongoDB 5.0, you can also reshard your collection by providing a new shard key for the collection.从MongoDB 5.0开始，您还可以通过为集合提供新的分片键来重分片集合。

To refine a collection's shard key, use the refineCollectionShardKey command. 要优化集合的分片键，请使用refineCollectionShardKey命令。The refineCollectionShardKey adds a suffix field or fields to the existing key to create the new shard key.refineCollectionShardKey向现有密钥添加一个或多个后缀字段，以创建新的分片键。

For example, you may have an existing orders collection in a test database with the shard key { customer_id: 1 }. 例如，您可能在test数据库中有一个现有的orders集合，其分片键为{ customer_id: 1 }。You can use the refineCollectionShardKey command to change the shard key to the new shard key { customer_id: 1, order_id: 1 }:您可以使用refineCollectionShardKey命令将分片键更改为新的分片键{ customer_id: 1, order_id: 1 }：

db.adminCommand( {
   refineCollectionShardKey: "test.orders",
   key: { customer_id: 1, order_id: 1 }
} )
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