setFeatureCompatibilityVersion (database command数据库命令)

setFeatureCompatibilityVersion

Required

The possible values for version are:version的可能值为：

confirm确认

Required必需的

Set to true to confirm the feature compatibility change and allow the operation to proceed.设置为true以确认功能兼容性更改并允许操作继续。

If you omit the confirm parameter or set confirm to a value other than true, the command fails and returns a warning about modifying the feature compatibility version. 如果省略confirm参数或将confirm设置为true以外的值，则该命令将失败，并返回有关修改功能兼容性版本的警告。The warning states that after you upgrade or downgrade your cluster's FCV, you cannot downgrade the binary version without support assistance.警告指出，升级或降级集群的FCV后，如果没有支持帮助，您将无法降级二进制版本。

writeConcern

Optional可选

The writeConcern specifies the write concern wtimeout value in milliseconds:writeConcern指定写入关注wtimeout值（以毫秒为单位）：

• The time period that the primary waits for acknowledgment from the majority of the replica set members. If the acknowledgment is not received in the time period, the operation fails.primary等待大多数副本集成员确认的时间段。如果在该时间段内未收到确认，则操作失败。
• Default is 60000 milliseconds. 默认值为60000毫秒。Use a longer time period if the secondary members of the replica set have a delay that exceeds the wtimeout default.如果副本集的secondary成员的延迟超过wtimeout默认值，请使用更长的时间段。

Downgrade with Backward-Incompatible Data因数据向后不兼容而降级

If you try to downgrade the FCV of a cluster that contains incompatible data in the downloaded version, you receive a CannotDowngrade error. When this error occurs, the cluster remains in the transitionary downgrading state.如果您尝试降级下载版本中包含不兼容数据的集群的FCV，您将收到CannotDowngrade错误。当发生此错误时，集群仍处于过渡降级状态。

To move the cluster out of the downgrading state, either:要将集群移出downgrading（降级）状态，请执行以下操作之一：

• Modify your cluster data to remove backwards-incompatible features, then re-run the setFeatureCompatibilityVersion command with the downgraded version to set the FCV to the downgraded version.修改集群数据以删除向后不兼容的功能，然后使用降级版本重新运行setFeatureCompatibilityVersion命令，将FCV设置为降级版本。

• Run the setFeatureCompatibilityVersion command with the original upgraded version to set the FCV back to the original version.使用原始升级版本运行setFeatureCompatibilityVersion命令，将FCV设置回原始版本。

  Important

  Setting the FCV to the original version stops the downgrade procedure and changes the FCV back to the upgraded version. This procedure does not reset the cluster back to the state before the FCV downgrade began.将FCV设置为原始版本会停止降级过程，并将FCV更改回升级版本。此过程不会将群集重置回FCV降级开始前的状态。

  If a failed FCV downgrade's internal metadata is not cleaned up, any subsequent FCV upgrade attempt fails with an error message. You must complete the FCV downgrade before trying to upgrade the FCV.如果失败的FCV降级的内部元数据未被清理，则任何后续的FCV升级尝试都会失败，并显示错误消息。在尝试升级FCV之前，您必须完成FCV降级。

Downgrade Policy Changes in MongoDB 7.0MongoDB 7.0中的降级策略更改

Starting in MongoDB 7.0, you cannot downgrade your deployment's FCV to or from a minor release version of MongoDB.从MongoDB 7.0开始，您不能将部署的FCV降级到MongoDB的次要版本或从MongoDB的次要发布版本降级。

If you upgrade or downgrade your deployment's FCV, you cannot downgrade your deployment's binary version without assistance from support.如果升级或降级部署的FCV，则在没有支持人员帮助的情况下，无法降级部署的二进制版本。

To learn more, see Downgrade 7.0 to 6.0.要了解更多信息，请参阅降级7.0到6.0。

Conflicts with Background Operations与后台操作冲突

Certain background operations may prevent execution of setFeatureCompatibilityVersion. Use currentOp to identify any ongoing operations.某些后台操作可能会阻止执行setFeatureCompatibilityVersion。使用currentOp识别任何正在进行的操作。

Sync Failures同步失败

If you trigger a setFeatureCompatibilityVersion change during an initial sync, the sync may fail with an OplogOperationUnsupported error message when replaying entries on the oplog application phase. 如果在初始同步期间触发setFeatureCompatibilityVersion更改，则在oplog应用程序阶段重放条目时，同步可能会失败，并显示OplogOperationUnsupported错误消息。The sync following this attempt succeeds because the operation phase no longer replays the operation.此尝试后的同步成功，因为操作阶段不再重放操作。

Default Values默认值

Idempotency幂等性

This command must perform writes to an internal system collection. If for any reason the command does not complete successfully, you can safely retry the command as the operation is idempotent.此命令必须对内部系统集合执行写入操作。如果由于任何原因命令未成功完成，您可以安全地重试该命令，因为该操作是幂等的。

Cluster-to-Cluster Sync and User Write Blocking群集到群集同步和用户写入阻止

Starting in MongoDB 6.0, if you need to downgrade the feature compatibility version, ensure you disable cluster-to-cluster replication and user write blocking.从MongoDB 6.0开始，如果需要降级功能兼容性版本，请确保禁用集群到集群的复制和用户写阻塞。

1. If you enabled cluster-to-cluster replication, disable it.如果启用了群集到群集复制，请禁用它。

2. If you enabled user write blocking, disable it:如果启用了用户写阻止，请禁用它：

   db.runCommand( { setUserWriteBlockMode: 1, global: false } )

3. Wait for the previous command to complete.等待上一个命令完成。
4. Downgrade the feature compatibility version using setFeatureCompatibilityVersion.使用setFeatureCompatibilityVersion降级功能兼容性版本。

For more information on MongoDB Cluster-to-Cluster Sync, see the documentation.有关MongoDB集群到集群同步的更多信息，请参阅文档。

Feature Compatibility in ArbitersArbiters中的功能兼容性

Arbiters do not replicate the admin.system.version collection. Because of this, arbiters always have a feature compatibility version equal to the downgrade version of the binary, regardless of the FCV value of the replica set.仲裁器不会复制admin.system.version集合。因此，无论副本集的FCV值如何，仲裁器的功能兼容性版本始终等于二进制文件的降级版本。

For example, an arbiter in a MongoDB 5.0 cluster, has an FCV value of 4.4.例如，MongoDB 5.0集群中的仲裁器的FCV值为4.4。

Get 获取FeatureCompatibilityVersion

To view the featureCompatibilityVersion for a mongod instance, run the getParameter command on a mongod instance:要查看mongd实例的featureCompatibilityVersion，请在mongod实例上运行getParameter命令：

db.adminCommand(
   {
      getParameter: 1,
      featureCompatibilityVersion: 1
   }
 )

The output resembles:输出类似于：

{
  featureCompatibilityVersion: { version: '5.0' },
  ok: 1,
  '$clusterTime': {
    clusterTime: Timestamp({ t: 1660318752, i: 5 }),
    signature: {
      hash: Binary(Buffer.from("ce0cff3621e9b089fa6d8e9a1e1efc1a1ff15dab", "hex"), 0),
      keyId: Long("7129893797260951557")
    }
  },
  operationTime: Timestamp({ t: 1660318752, i: 5 })
}

Set Feature Compatibility Version on MongoDB 7.0 Deployments在MongoDB 7.0部署上设置功能兼容版本

db.adminCommand(
   {
      setFeatureCompatibilityVersion: "7.0",
      confirm: true
   }
)

db.adminCommand(
   {
      setFeatureCompatibilityVersion: "6.0",
      confirm: true
   }
)

Set Feature Compatibility Version on MongoDB 6.0 Deployments在MongoDB 6.0部署上设置功能兼容版本

db.adminCommand( { setFeatureCompatibilityVersion: "6.0" } )

db.adminCommand( { setFeatureCompatibilityVersion: "5.0" } )

Set Write Concern Timeout设置写入关注超时

The following example sets the optional write concern wtimeout field to 5000 (5 seconds).以下示例将可选的写入关注wtimeout字段设置为5000(5秒）。

db.adminCommand( {
   setFeatureCompatibilityVersion: "5.0",
   writeConcern: { wtimeout: 5000 }
} )