moveChunk (database command数据库命令)

Definition定义

moveChunk

Internal administrative command. Moves chunks between shards. 内部行政指挥。在分片之间移动块。Issue the moveChunk command via a mongos instance while using the admin database. Use the following forms:在使用admin数据库时，通过mongos实例发出moveChunk命令。使用以下表格：

Tip

In mongosh, this command can also be run through the sh.moveChunk() helper method.在mongosh中，此命令也可以通过sh.moveChunk()辅助方法运行。

Helper methods are convenient for mongosh users, but they may not return the same level of information as database commands. 助手方法对mongosh用户来说很方便，但它们可能不会返回与数据库命令相同级别的信息。In cases where the convenience is not needed or the additional return fields are required, use the database command.如果不需要便利性或需要额外的返回字段，请使用database命令。

db.adminCommand( { moveChunk : <namespace> ,
                 find : <query> ,
                 to : <ID of the recipient shard>,
                 forceJumbo: <boolean>,
                 _secondaryThrottle : <boolean>,
                 writeConcern: <document>,
                 _waitForDelete : <boolean> } )

Alternatively:或者：

db.adminCommand( { moveChunk : <namespace> ,
                 bounds : <array> ,
                 to : <ID of the recipient shard>,
                 forceJumbo: <boolean>,
                 _secondaryThrottle : <boolean>,
                 writeConcern: <document>,
                 _waitForDelete : <boolean> } )

Note

Use the listShards command to retrieve the ID of the recipient shard.使用listShards命令检索收件人分片的ID。

The moveChunk command has the following fields:moveChunk命令有以下字段：

Field字段	Type类型	Description描述
moveChunk	string字符串	The namespace of the collection where the chunk exists. Specify the collection's full namespace, including the database name.块所在集合的命名空间。指定集合的完整命名空间，包括数据库名称。
find	document文档	An equality match on the shard key that specifies the shard-key value of the chunk to move. Specify either the bounds field or the find field but not both. 分片键上的相等匹配，指定要移动的块的分片键值。指定bounds字段或find字段，但不能同时指定两者。Do not use the find field to select chunks in collections that use a hashed shard key.不要使用find字段来选择使用哈希分片键的集合中的块。
bounds	array数组	The bounds of a specific chunk to move. The array must consist of two documents that specify the lower and upper shard key values of a chunk to move. 要移动的特定块的边界。数组必须由两个文档组成，这两个文档指定要移动的块的下分片键值和上分片键值。Specify either the bounds field or the find field but not both. Use bounds to select chunks in collections that use a hashed shard key.指定bounds字段或find字段，但不能同时指定两者。使用bounds在使用哈希分片键的集合中选择块。
to	string字符串	The ID of the recipient shard for the chunk.块的接收方分片的ID。
forceJumbo	boolean布尔值	Optional. 可选。A flag that determines if the command can move a chunk that is too large to migrate. The chunk may or may not be labeled as jumbo.一个标志，用于确定命令是否可以移动太大而无法迁移的块。该块可能被标记为巨型，也可能没有。 If true, the command can move the chunk.如果为true，则该命令可以移动块。 If false, the command cannot move the chunk.如果为false，则该命令无法移动块。 The default is false.默认值为false。 WARNING:警告： The moveChunk command with forceJumbo=true blocks write operations on the collection.带有forceJumbo=true的moveChunk命令阻止对集合的写入操作。 This option causes the shard to migrate chunks even when they are larger than the configured chunk size. The collection remains unavailable for writes for the duration of the migration.此选项会导致分片迁移块，即使它们大于配置的块大小。在迁移期间，该集合仍不可用于写入。 To migrate these large chunks without this long blocking period, see Balance Ranges that Exceed Size Limit instead.要迁移这些大块而不需要这么长的阻塞期，请参阅超过大小限制的平衡范围。
_secondaryThrottle	boolean布尔值	Optional. 可选。For WiredTiger, defaults to false.对于WiredTiger，默认值为false。 If true, then by default, each document move during chunk migration propagates to at least one secondary before the balancer proceeds with the next document. 如果为true，则默认情况下，块迁移期间的每个文档移动都会在平衡器继续处理下一个文档之前传播到至少一个辅助文档。This is equivalent to a write concern of { w: 2 }.这相当于{w:2}的写入关注。 Use the writeConcern option to specify a different write concern.使用writeConcern选项指定其他写入关注。 If false, the balancer does not wait for replication to a secondary and instead continues with the next document.如果为false，则平衡器不会等待复制到辅助文档，而是继续处理下一个文档。 For more information, see Secondary Throttle.有关更多信息，请参阅辅助阀门。
writeConcern	document文档	Optional. 可选。A document that expresses the write concern that the _secondaryThrottle will use to wait for secondaries during the chunk migration.一个文档，表示_sesecondaryThrottle在块迁移期间将用于等待二级的写入关注。 writeConcern requires _secondaryThrottle: true.
_waitForDelete	boolean布尔值	Optional. 可选。If set to true, the delete phase of a moveChunk operation is blocking. 如果设置为true，则moveChunk操作的删除阶段将被阻塞。_waitForDelete defaults to false.默认为false。 When the _waitForDelete field is set, MongoDB does not wait on the orphanCleanupDelaySecs delay before performing the range deletion. 当设置_waitForDelete字段时，MongoDB在执行范围删除之前不会等待orphanCleanupDelaySecs延迟。If you use the _waitForDelete parameter and have any read operations occurring on secondaries, the read might terminate due to the migration's delete phase. 如果使用_waitForDelete参数并在次服务器上进行任何读取操作，则读取可能会因迁移的删除阶段而终止。To learn more, see terminateSecondaryReadsOnOrphanCleanup.要了解更多信息，请参阅terminateSecondaryReadsOnOrphanCleanup。

The value of bounds takes the form:bounds值的形式如下：

[ { hashedField : <minValue> } ,
  { hashedField : <maxValue> } ]

The chunk migration section describes how chunks move between shards on MongoDB.块迁移部分描述了块如何在MongoDB上的分片之间移动。

Compatibility兼容性

This command is available in deployments hosted in the following environments:此命令在以下环境中托管的部署中可用：

• MongoDB Atlas: The fully managed service for MongoDB deployments in the cloud：云中MongoDB部署的完全托管服务

• MongoDB Enterprise: The subscription-based, self-managed version of MongoDB：MongoDB的基于订阅的自我管理版本
• MongoDB Community: The source-available, free-to-use, and self-managed version of MongoDB：MongoDB的源代码可用、免费使用和自我管理版本

Considerations注意事项

Only use the moveChunk in special circumstances such as preparing your sharded cluster for an initial ingestion of data, or a large bulk import operation. In most cases allow the balancer to create and balance chunks in sharded clusters. See Create Ranges in a Sharded Cluster for more information.仅在特殊情况下使用moveChunk，例如为初始数据摄取或大批量导入操作准备分片集群。在大多数情况下，允许平衡器在分片集群中创建和平衡块。有关详细信息，请参阅在分片群集中创建范围。

Behavior行为

errmsg: "The collection's metadata lock is already taken."