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. The warning states that after you upgrade or downgrade your cluster's FCV, you cannot downgrade the binary version without support assistance.

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。

使用前向不兼容数据进行升级

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.

出现此错误时，请执行以下任一操作：

• 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 reverts the FCV to the downgraded version. The cluster does not return to its 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 also fail with an error message. You must complete the FCV upgrade before you can 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 incompatible data in the downloaded version, you receive a CannotDowngrade error. When this error occurs, the cluster remains in the transitionary downgrading state.

要将集群移出 downgrading 状态，请执行以下任一操作：

• 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

  Setting the FCV to the original version stops the downgrade procedure and reverts the FCV to the upgraded version. The cluster does not return to its state before the FCV downgrade began.

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

MongoDB 7.0 中的降级策略变更

从 MongoDB 7.0 开始，您无法将部署的 FCV 降级到 MongoDB 的快速发布版或从快速发布版降级。

如果您升级或降级部署的 fCV，没有支持人员的帮助，您无法降级部署的二进制版本。

要了解详情，请参阅《将 7.0 降级至 6.0》。

与后台操作冲突

Certain background operations may prevent execution of setFeatureCompatibilityVersion. Use currentOp to identify any ongoing operations.

同步失败

If you change the FCV during an initial sync, the sync may fail with an OplogOperationUnsupported error when replaying entries on the oplog application phase. The next sync succeeds because the operation phase no longer replays the operation.

Default Values

幂等

此命令必须对内部系统集合执行写入操作。如果命令未能成功完成，则可安全地重试。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. Downgrade the feature compatibility version using setFeatureCompatibilityVersion.

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 })
}

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
   }
)

为 MongoDB 6.0 部署设置特征兼容性版本

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

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

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 }
} )