sh.reshardCollection()

Initialization Phase初始化阶段

During the initialization phase, the resharding coordinator determines the new data distribution for the sharded collection.在初始化阶段，重新分片协调器确定分片集合的新数据分布。

Index Phase索引阶段

During the index phase:在索引阶段：

• Each shard recipient creates a new, empty sharded collection with the same collection options as the existing sharded collection. 每个分片接收者都会创建一个新的空分片集合，该集合具有与现有分片集合相同的集合选项。This new sharded collection is the target for where recipient shards write the new data.这个新的分片集合是接收方分片写入新数据的目标。
• Each shard recipient builds the necessary new indexes. 每个分片接收者都构建必要的新索引。These include all existing indexes on the sharded collection and an index compatible with the new shard key pattern if such an index doesn’t already exist on the sharded collection.其中包括分片集合上的所有现有索引，以及与新的分片键模式兼容的索引（如果分片集合中还不存在这样的索引）。

Clone, Apply, and Catch-up Phase克隆、应用和追赶阶段

During the clone, apply, and catch-up phase:在克隆、应用和追赶阶段：

• Each shard recipient clones an initial copy of the documents it would own under the new shard key.每个分片接收者都会在新的分片键下克隆其将拥有的文档的初始副本。
• Each shard recipient begins applying oplog entries from operations that happened after the recipient cloned the data.每个分片接收方都开始应用接收方克隆数据后发生的操作中的oplog条目。
• When the estimate for the time remaining to complete the resharding operation is under two seconds, the resharding coordinator blocks writes for the collection.当完成重新分片操作的剩余时间估计不到两秒时，重新分片协调器会阻止对集合的写入。
  Note

  If desired, you can manually force the resharding operation to complete by issuing the sh.commitReshardCollection() method. 如果需要，可以通过发出sh.commitReshardCollection()方法手动强制完成重新分片操作。This is useful if the current time estimate to complete the resharding operation is an acceptable duration for your collection to block writes. 如果完成重新分片操作的当前时间估计值是集合阻止写入的可接受持续时间，则此选项非常有用。The sh.commitReshardCollection() method blocks writes early and forces the resharding operation to complete. sh.commitReshardCollection()方法会提前阻止写入并强制完成重新分片操作。During the time period where writes are blocked your application experiences an increase in latency.在写入被阻止的时间段内，应用程序的延迟会增加。

Commit Phase提交阶段

• Once the resharding process reaches the commit phase, it may no longer be aborted with sh.abortReshardCollection().一旦重新分片过程到达提交阶段，它可能不再使用sh.abortReshardCollection()中止。
• When all shards have reached strict consistency, the resharding coordinator commits the resharding operation and installs the new routing table.当所有分片都达到严格的一致性时，重新分片协调器提交重新分片操作并安装新的路由表。
• The resharding coordinator instructs each donor and recipient shard primary, independently, to rename the temporary sharded collection. The temporary collection becomes the new resharded collection.重新分片协调器分别指示每个施主和受主分片器重命名临时分片集合。临时集合将成为新的重新分片的集合。
• Each donor shard drops the old sharded collection.每个捐赠分片都会丢弃旧的分片集合。
  Tip

  See also: 另请参阅：

  Reshard a Collection重新分片集合

Reshard a Collection重新分片集合

The following example reshards the sales.orders collection with the new shard key { order_id: 1 }:以下示例使用新的分片键{ order_id: 1 }重新分片sales.orders集合：

sh.reshardCollection("sales.orders", { order_id: 1 })

MongoDB returns the following:MongoDB返回以下内容：

{
  ok: 1,
  '$clusterTime': {
    clusterTime: Timestamp(1, 1624887954),
    signature: {
      hash: Binary(Buffer.from("0000000000000000000000000000000000000000", "hex"), 0),
      keyId: 0
    }
  },
  operationTime: Timestamp(1, 1624887947)
}