setFeatureCompatibilityVersion（数据库命令）

setFeatureCompatibilityVersion

必需

version 的可能值是：

确认

必需

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.

writeConcern

Optional

writeConcern 以毫秒为单位指定写关注 wtimeout 值：

• 主节点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。

• 默认值为 60000 毫秒。如果副本集的次要成员的延迟超过 wtimeout 默认值，则使用更长的时间段。

干运行

Optional

If set to true, MongoDB simulates an upgrade or downgrade of the feature compatibility version. If the cluster contains incompatible data, the operation fails with an error.

Upgrade with Forward-Incompatible Data

If you try to upgrade the FCV of a cluster that contains forwards-incompatible data in the upgraded version, you receive a CannotUpgrade error. Forwards-incompatible data can refer to any data in your cluster that relies on a feature that was removed in the target version.

When this error occurs, either:

• Modify your cluster data to remove forwards-incompatible features, then re-run the setFeatureCompatibilityVersion command with the upgraded version to set the FCV to the upgraded version.

• Run the setFeatureCompatibilityVersion command with the original downgraded version to set the FCV back to the original version.

  重要

  Setting the FCV to the original version stops the upgrade procedure and changes the FCV back to the downgraded version. This procedure does not reset the cluster back to the state before the FCV upgrade began.

  If the FCV upgrade confirms that there is no forwards-incompatible data but otherwise stops or fails, any subsequent FCV downgrade attempts will also fail with an error message. You must complete the FCV upgrade before trying to downgrade the FCV.

使用向后不兼容的数据进行降级

If you try to downgrade the FCV of a cluster that contains backwards-incompatible data in the downgraded version, you receive a CannotDowngrade error. Backwards-incompatible data can refer to any data in your cluster that relies on a feature that isn't available in the target version.

When this error occurs, either:

• 修改集群数据以删除向后兼容的功能，然后使用降级版本重新运行 setFeatureCompatibilityVersion 命令，将 fCV 设置为降级版本。

• 使用原始升级版本运行 setFeatureCompatibilityVersion 命令，以便将 fCV 重新设置为原始版本。

  重要

  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。此过程不会将集群重置回到 FcV 降级开始之前的状态。

  If the FCV downgrade confirms that there is no backwards-incompatible data but otherwise stops or fails, any subsequent FCV upgrade attempts will also fail with an error message. You must complete the FCV downgrade before trying to upgrade the FCV.

Downgrade Policy in MongoDB 8.3

Starting in 8.3, you can downgrade your deployment's FCV to the immediately previous minor version.

要学习；了解更多信息，请参阅将8.3降级至8.2 。

与后台操作冲突

某些后台操作可能会阻止 setFeatureCompatibilityVersion 的执行。使用 currentOp 确定任何正在进行的操作。

同步失败

如果在初始同步过程中触发 setFeatureCompatibilityVersion 更改，在 oplog 应用阶段重放条目时，同步可能会失败，并显示 OplogOperationUnsupported 错误信息。此尝试之后的同步会成功，因为操作阶段不再重放该操作。

Default Values

幂等

此命令执行的必须是对内部系统集合的写入。如果由于任何原因该命令未能成功完成，您都可以安全地重试该命令，因为该操作是幂等的。

Cluster-to-Cluster Sync 和用户写入阻塞

从 MongoDB 6.0 开始，如果需要降级特征兼容性版本，请确保禁用集群到集群复制和用户写入阻止。

1. 如果您启用了集群到集群复制，请将其禁用。

2. 如果启用了用户写入阻止，请将其禁用：

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

3. 等待上一条命令完成。

4. 使用 setFeatureCompatibilityVersion 降级特征兼容性版本。

有关 MongoDB Cluster-to-Cluster Sync 的更多信息，请参阅文档。

仲裁节点中的功能兼容性

仲裁节点不会复制 admin.system.version 集合。因此，无论副本集的 fCV 值如何，仲裁节点始终具有等于二进制文件的降级版本的特征兼容性版本。

示例， MongoDB 5.0集群中的仲裁节点的FCV值为 4.4。

获取 FeatureCompatibilityVersion

要查看 mongod 实例的 featureCompatibilityVersion，请在 mongod 实例上运行 getParameter 命令：

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

输出类似如下所示：

{
  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 8.0 Deployments

db.adminCommand(
   {
      setFeatureCompatibilityVersion: "8.0",
      confirm: true
   }
)

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

在 MongoDB 7.0 部署上设置功能兼容性版本

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

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

设置写关注超时

以下示例将可选写关注 wtimeout 字段设置为 5000（5 秒）。

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