Change a Shard Key更改分片键

The ideal shard key allows MongoDB to distribute documents evenly throughout the cluster while facilitating common query patterns. 理想的分片键允许MongoDB在整个集群中均匀分布文档，同时促进常见的查询模式。A suboptimal shard key can lead to uneven data distribution and the following problems:次优的分片键可能会导致数据分布不均匀以及以下问题：

• Jumbo chunks
• Uneven load distribution负荷分布不均
• Decreased query performance over time随着时间的推移，查询性能下降

To address these issues, MongoDB allows you to change your shard key:为了解决这些问题，MongoDB允许您更改分片键：

• Starting in MongoDB 5.0, you can reshard a collection by changing a collection's shard key.从MongoDB 5.0开始，您可以通过更改集合的分片键来重分片集合。
• Starting in MongoDB 4.4, you can refine a shard key by adding a suffix field or fields to the existing shard key.从MongoDB 4.4开始，您可以通过向现有分片键添加一个或多个后缀字段来优化分片键。

In MongoDB 4.2 and earlier, a document's shard key is immutable.在MongoDB 4.2及更早版本中，文档的shard键是不可变的。

For more information on common performance and scaling issues and advice on how to fix them, read Troubleshoot Shard Keys.有关常见性能和扩展问题的更多信息以及如何解决这些问题的建议，请阅读分片键疑难解答。