Manage Sharded Cluster Balancer管理分片集群平衡器

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). 检查平衡器是否启用（即允许平衡器运行）。sh.getBalancerState() does not check if the balancer is actively migrating data.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, run the following command, which returns a boolean:要查看分片集群中是否启用了平衡器，请运行以下命令，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()查看是否启用了平衡器。The currently-enabled field indicates whether the balancer is enabled, and the currently-running field indicates if the balancer is currently running.currently-enabled字段指示平衡器是否已启用，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:要查看平衡器进程是否在集群中处于活动状态，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. In most situations, the default size is appropriate for splitting and migrating chunks. For information on how range size affects deployments, see details, see Range Size.分片集群的默认范围大小为128 MB。在大多数情况下，默认大小适合分割和迁移块。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范围，但不会追溯影响所有范围。

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并且迁移会影响性能时，确保平衡器仅在特定时间处于活动状态是有用的。By default, the balancer process is always enabled and migrating chunks. The following procedure specifies the activeWindow, which is the timeframe during which the balancer is able to migrate chunks:默认情况下，平衡器进程始终处于启用状态并迁移块。以下过程指定了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 }
)

Check Balancing Window检查平衡窗口

To see the current balancing window, run the following command:要查看当前的平衡窗口，请运行以下命令：

use config
db.settings.find( { _id: "balancer" } )

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 $unset to clear the activeWindow, as in the following:如果您已设置平衡窗口并希望删除计划，以便平衡器始终运行，请使用$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. To disable the balancer for a short period of time and prevent all migration, use the following procedure:默认情况下，平衡器可以随时运行，并且只在需要时移动块。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:执行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。

3. To verify that the balancer won't start, run the following command, which returns false if the balancer is disabled:要验证平衡器不会启动，请运行以下命令，如果平衡器被禁用，则返回false：

   sh.getBalancerState()

   Optionally, to verify no migrations are in progress after disabling, run the following operation in the mongosh shell:（可选）要验证禁用后没有正在进行的迁移，请在mongosh shell中运行以下操作：

   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:如果您已禁用平衡器并准备重新启用它，请使用此过程：

1. Connect to any mongos in the cluster using the mongosh shell.

2. Issue one of the following operations to enable the balancer:执行以下操作之一以启用平衡器：

   From the mongosh shell, issue:来自猫鼬壳，问题：

   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 } )

Disable Balancing During Backups禁用备份期间的平衡

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admin块，您可能会以分片集群的不一致快照结束。Never run a backup while the balancer is active. To ensure that the balancer is inactive during your backup operation:平衡器处于活动状态时，切勿运行备份。为确保平衡器在备份操作期间处于非活动状态：

• 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。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. The balancer completes the chunk move in-progress and then ceases all further balancing rounds.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。平衡器完成正在进行的块移动，然后停止所有进一步的平衡轮。

Before starting a backup operation, confirm that the balancer is not active. You can use the following command to determine if the balancer is active:在开始备份操作之前，请确认平衡器未处于活动状态。您可以使用以下命令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. 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.您可以使用sh.disableBalancing()方法禁用特定集合的平衡。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，例如在数据摄入或数据导出期间。

When you disable balancing on a collection, MongoDB will not interrupt in progress migrations.当您禁用集合上的平衡时，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在集合上启用平衡

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. However, if the data in your sharded collection is not balanced, MongoDB will be able to begin distributing the data more evenly.当您为集合启用平衡时，MongoDB不会立即开始平衡数据。但是，如果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. For example:要确认是否启用或禁用了集合的平衡，请在config数据库中查询collections集合命名空间中的集合集合集合，并检查noBalance字段。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. Balancing of this collection will begin the next time the balancer runs.如果结果为false，则当前已启用平衡，但过去已禁用该集合的平衡。下次平衡器运行时，将开始对此集合进行平衡。
• If the operation returns no output, balancing is enabled currently and has never been disabled in the past for this collection. Balancing of this collection will begin the next time the balancer runs.如果操作没有返回输出，则当前启用了平衡，并且过去从未为此集合禁用过平衡。下次平衡器运行时，将开始对此集合进行平衡。

You can also see if the balancer is enabled using sh.status(). 您还可以使用sh.status()查看是否启用了平衡器。The currently-enabled field indicates if the balancer is enabled.currently-enabled的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 }
)