Manage Sharded Cluster Balancer管理分片化群集平衡器

Check the Balancer State检查平衡器状态

sh.getBalancerState() checks if the balancer is enabled (i.e. that the balancer is permitted to run). sh.getBalancerState() does not check if the balancer is actively migrating data.sh.getBalancerState()检查平衡器是否已启用（即是否允许平衡器运行）。sh.getBalancerState()不检查平衡器是否正在主动迁移数据。

To see if the balancer is enabled in your sharded cluster, issue the following command, which returns a boolean:要查看您的分片集群中是否启用了平衡器，请发出以下命令，该命令返回一个布尔值：

sh.getBalancerState()

You can also see if the balancer is enabled using sh.status(). 您还可以使用sh.status()查看平衡器是否已启用。The currently-enabled field indicates whether the balancer is enabled, while the currently-running field indicates if the balancer is currently running.currently-enabled用字段指示平衡器是否已启用，而currently-running字段指示平衡器当前是否正在运行。

Check if Balancer is Running检查平衡器是否正在运行

To see if the balancer process is active in your cluster:要查看平衡器进程在集群中是否处于活动状态，请执行以下操作：

1. Connect to any mongos in the cluster using the mongosh shell.使用mongosh shell连接到集群中的任何mongos。
2. Use the following operation to determine if the balancer is running:使用以下操作来确定平衡器是否正在运行：

   sh.isBalancerRunning()

Configure Default Range Size配置默认范围大小

The default range size for a sharded cluster is 128 megabytes. 分片集群的默认范围大小为128兆字节。In most situations, the default size is appropriate for splitting and migrating chunks. 在大多数情况下，默认大小适用于分割和迁移块。For information on how range size affects deployments, see details, see Range Size.有关范围大小如何影响部署的信息，请参阅详细信息，请参阅范围大小。

Changing the default range size affects ranges that are processes during migrations and auto-splits but does not retroactively affect all ranges.更改默认范围大小会影响迁移和自动拆分过程中的进程范围，但不会追溯到所有范围。

Starting in MongoDB 6.1, automatic chunk splitting is not performed. 从MongoDB 6.1开始，不执行自动区块分割。This is because of balancing policy improvements. 这是因为平衡政策的改进。Auto-splitting commands still exist, but do not perform an operation. 自动拆分命令仍然存在，但不执行操作。For details, see Balancing Policy Changes.有关详细信息，请参阅平衡策略更改。

To configure default range size, see Modify Range Size in a Sharded Cluster.要配置默认范围大小，请参阅修改分片群集中的范围大小。

Schedule the Balancing Window安排平衡窗口

In some situations, particularly when your data set grows slowly and a migration can impact performance, it is useful to ensure that the balancer is active only at certain times. 在某些情况下，特别是当数据集增长缓慢且迁移可能影响性能时，确保平衡器仅在特定时间处于活动状态是非常有用的。The following procedure specifies the activeWindow, which is the timeframe during which the balancer will be able to migrate chunks:以下过程指定activeWindow，这是平衡器能够迁移块的时间段：

use config

sh.startBalancer()

db.settings.updateOne(
   { _id: "balancer" },
   { $set: { activeWindow : { start : "<start-time>", stop : "<stop-time>" } } },
   { upsert: true }
)

Remove a Balancing Window Schedule删除平衡窗口计划

If you have set the balancing window and wish to remove the schedule so that the balancer is always running, use $unset to clear the activeWindow, as in the following:如果您已经设置了平衡窗口，并希望删除时间表，以便平衡器始终运行，请使用$unset清除activeWindow，如下所示：

use config
db.settings.updateOne( { _id : "balancer" }, { $unset : { activeWindow : true } } )

Disable the Balancer禁用平衡器

By default, the balancer may run at any time and only moves chunks as needed. 默认情况下，平衡器可以在任何时候运行，并且只根据需要移动块。To disable the balancer for a short period of time and prevent all migration, use the following procedure:要在短时间内禁用平衡器并阻止所有迁移，请使用以下过程：

1. Connect to any mongos in the cluster using the mongosh shell.使用mongosh shell连接到集群中的任何mongos。
2. Issue the following operation to disable the balancer:发出以下操作以禁用平衡器：

   sh.stopBalancer()

   If a migration is in progress, the system will complete the in-progress migration before stopping.如果正在进行迁移，系统将在停止之前完成正在进行的迁移。

   Starting in MongoDB 6.1, automatic chunk splitting is not performed. This is because of balancing policy improvements. 从MongoDB 6.1开始，不执行自动区块分割。这是因为平衡政策的改进。Auto-splitting commands still exist, but do not perform an operation. 自动拆分命令仍然存在，但不执行操作。For details, see Balancing Policy Changes.有关详细信息，请参阅平衡策略更改。

   In MongoDB versions earlier than 6.1, sh.stopBalancer() also disables auto-splitting for the sharded cluster.在6.1之前的MongoDB版本中，sh.stopBalancer()还禁用了分片集群的自动拆分。

3. To verify that the balancer will not start, issue the following command, which returns false if the balancer is disabled:要验证平衡器是否不会启动，请发出以下命令，如果平衡器被禁用，则返回false：

   sh.getBalancerState()

   Optionally, to verify no migrations are in progress after disabling, issue the following operation in the mongosh shell:（可选）要验证禁用后没有迁移正在进行，请在mongosh shell中发出以下操作：

   use config
   while( sh.isBalancerRunning() ) {
             print("waiting...");
             sleep(1000);
   }

db.adminCommand( { balancerStop: 1 } )

Enable the Balancer启用平衡器

Use this procedure if you have disabled the balancer and are ready to re-enable it:如果已禁用平衡器并准备重新启用，请使用以下步骤：

1. Connect to any mongos in the cluster using the mongosh shell.使用mongosh shell连接到集群中的任何mongos。
2. Issue one of the following operations to enable the balancer:发出以下操作之一以启用平衡器：

   From the mongosh shell, issue:从mongosh shell发布：

   sh.startBalancer()

   Note

   To enable the balancer from a driver, use the balancerStart command against the admin database, as in the following:要从驱动程序启用平衡器，请对admin数据库使用balancerStart命令，如下所示：

   db.adminCommand( { balancerStart: 1 } )

   Starting in MongoDB 6.1, automatic chunk splitting is not performed. 从MongoDB 6.1开始，不执行自动区块分割。This is because of balancing policy improvements. 这是因为平衡政策的改进。Auto-splitting commands still exist, but do not perform an operation. 自动拆分命令仍然存在，但不执行操作。For details, see Balancing Policy Changes.有关详细信息，请参阅平衡策略更改。

   In MongoDB versions earlier than 6.1, sh.startBalancer() also enables auto-splitting for the sharded cluster.在6.1之前的MongoDB版本中，sh.startBalancer()还支持对分片集群进行自动拆分。

Disable Balancing During Backups在备份期间禁用平衡

If MongoDB migrates a chunk during a backup, you can end with an inconsistent snapshot of your sharded cluster. 如果MongoDB在备份过程中迁移了一个区块，那么您可能会得到一个不一致的分片集群快照。Never run a backup while the balancer is active. 平衡器处于活动状态时，切勿运行备份。To ensure that the balancer is inactive during your backup operation:要确保平衡器在备份操作期间处于非活动状态，请执行以下操作：

• Set the balancing window so that the balancer is inactive during the backup. Ensure that the backup can complete while you have the balancer disabled.设置平衡窗口，使平衡器在备份期间处于非活动状态。请确保在禁用平衡器的情况下可以完成备份。
• manually disable the balancer for the duration of the backup procedure.在备份过程期间手动禁用平衡器。

If you turn the balancer off while it is in the middle of a balancing round, the shut down is not instantaneous. 如果在平衡循环进行到一半时关闭平衡器，则关闭不是即时的。The balancer completes the chunk move in-progress and then ceases all further balancing rounds.平衡器完成正在进行的区块移动，然后停止所有进一步的平衡回合。

Before starting a backup operation, confirm that the balancer is not active. 在启动备份操作之前，请确认平衡器未处于活动状态。You can use the following command to determine if the balancer is active:您可以使用以下命令来确定平衡器是否处于活动状态：

!sh.getBalancerState() && !sh.isBalancerRunning()

When the backup procedure is complete you can reactivate the balancer process.备份过程完成后，您可以重新激活平衡器进程。

Disable Balancing on a Collection禁用集合上的平衡

You can disable balancing for a specific collection with the sh.disableBalancing() method. 您可以使用sh.disableBalancing()方法禁用特定集合的平衡。You may want to disable the balancer for a specific collection to support maintenance operations or atypical workloads, for example, during data ingestions or data exports.您可能希望禁用特定集合的平衡器，以支持维护操作或非典型工作负载，例如，在数据摄取或数据导出期间。

When you disable balancing on a collection, MongoDB will not interrupt in progress migrations.当您在集合上禁用平衡时，MongoDB不会中断正在进行的迁移。

To disable balancing on a collection, connect to a mongos with the mongosh shell and call the sh.disableBalancing() method.要禁用集合上的平衡，请使用mongosh shell连接到mongos并调用sh.disableBalancing()方法。

For example:例如：

sh.disableBalancing("students.grades")

The sh.disableBalancing() method accepts as its parameter the full namespace of the collection.sh.disableBalancing()方法接受集合的完整命名空间作为其参数。

Enable Balancing on a Collection对集合启用平衡

You can enable balancing for a specific collection with the sh.enableBalancing() method.您可以使用sh.enableBalancing()方法为特定集合启用平衡。

When you enable balancing for a collection, MongoDB will not immediately begin balancing data. 当您为集合启用平衡时，MongoDB不会立即开始平衡数据。However, if the data in your sharded collection is not balanced, MongoDB will be able to begin distributing the data more evenly.然而，如果您的分片集合中的数据不平衡，MongoDB将能够开始更均匀地分配数据。

To enable balancing on a collection, connect to a mongos with the mongosh shell and call the sh.enableBalancing() method.要在集合上启用平衡，请使用mongosh shell连接到mongos并调用sh.enableBalancing()方法。

For example:例如：

sh.enableBalancing("students.grades")

The sh.enableBalancing() method accepts as its parameter the full namespace of the collection.sh.enableBalancing()方法接受集合的完整命名空间作为其参数。

Confirm Balancing is Enabled or Disabled确认已启用或禁用平衡

To confirm whether balancing for a collection is enabled or disabled, query the collections collection in the config database for the collection namespace and check the noBalance field. 要确认集合的平衡是启用还是禁用，请在config数据库中查询集合命名空间的collections集合，并检查noBalance字段。For example:例如：

db.getSiblingDB("config").collections.findOne({_id : "students.grades"}).noBalance;

This operation will return a null error, true, false, or no output:此操作将返回null错误、true、false或无输出：

• A null error indicates the collection namespace is incorrect.null错误表示集合命名空间不正确。
• If the result is true, balancing is disabled.如果结果为true，则禁用平衡。
• If the result is false, balancing is enabled currently but has been disabled in the past for the collection. 如果结果为false，则当前已启用平衡，但过去已禁用集合的平衡。Balancing of this collection will begin the next time the balancer runs.此集合的平衡将在平衡器下次运行时开始。
• If the operation returns no output, balancing is enabled currently and has never been disabled in the past for this collection. 如果操作未返回任何输出，则当前已启用平衡，并且以前从未对此集合禁用过平衡。Balancing of this collection will begin the next time the balancer runs.此集合的平衡将在平衡器下次运行时开始。

You can also see if the balancer is enabled using sh.status(). 您还可以使用sh.status()查看平衡器是否已启用。The currently-enabled field indicates if the balancer is enabled.currently-enabled字段指示平衡器是否已启用。

Change Replication Behavior for Chunk Migration更改块迁移的复制行为

use config
db.settings.updateOne(
   { "_id" : "balancer" },
   { $set : { "_secondaryThrottle" : { "w": "majority" }  } },
   { upsert : true }
)

db.getSiblingDB("config").settings.updateOne(
   { _id: "balancer" },
   { $set: { attemptToBalanceJumboChunks : true } },
   { upsert: true }
)

Change the Maximum Storage Size for a Given Shard更改给定分片的最大存储大小

Changing a shard's maximum storage size is deprecated. 不赞成更改分片的最大存储大小。Starting in version 4.2, MongoDB uses the WiredTiger Storage Engine to manage how data is stored. WiredTiger compresses data to minimize storage use. 从4.2版本开始，MongoDB使用WiredTiger存储引擎来管理数据的存储方式。WiredTiger压缩数据以最大限度地减少存储使用。To learn more, see Compression.要了解更多信息，请参阅压缩。

For MongoDB versions 6.1 and earlier, you can still set a maximum storage size for a given shard in the sharded cluster by using the maxSize field. 对于MongoDB 6.1及更早版本，您仍然可以使用maxSize字段为分片集群中的给定分片设置最大存储大小。You can find configuration data related to shards in the config.shards collection.您可以在config.shards集合中找到与分片相关的配置数据。

Starting in version 6.2, MongoDB removes the maxSize field from the addShard command. As a result:从6.2版本开始，MongoDB从addShard命令中删除了maxSize字段。因此：

• Running addShard with the maxSize field returns an InvalidOptions error.使用maxSize字段运行addShard会返回InvalidOptions错误。
• New documents in the shards collection no longer include the maxSize field.shards集合中的新文档不再包含maxSize字段。
• Any pre-existing maxSize field entries are ignored.任何预先存在的maxSize字段条目都将被忽略。