setDefaultRWConcern（数据库命令）

副本集

Issue setDefaultRWConcern against the replica set primary. The primary replicates the new global default settings to the remaining members of the replica set. Secondaries which have not yet replicated the updated global default settings continue using their local 'stale' copy of the defaults.

Issue the setDefaultRWConcern command with a writeConcern of w : "majority" to ensure the command only returns after the changes have propagated to a majority of replica set members.

分片集群

Issue the setDefaultRWConcern against a mongos in the cluster. The mongos persists the updated settings to the config server replica set (CSRS). Each mongos periodically issues a getDefaultRWConcern against the CSRS to refresh their local copy of the global settings. A mongos uses its local 'stale' copy of the global defaults during the time period between refreshes.

Issue the setDefaultRWConcern command with a writeConcern of w : "majority" to ensure the command only returns after the changes have propagated to a majority of CSRS members.

当应用程序在未明确指定读关注或写关注设置的情况下针对 mongos 执行操作时，mongos 将应用相应的全局默认设置。

The global default settings do not propagate to the individual shards. You cannot run setDefaultRWConcern against a shard.

访问控制

For replica sets or sharded clusters enforcing Authentication on Self-Managed Deployments, setDefaultRWConcern requires that the authenticated user have the setDefaultRWConcern privilege action.

The clusterManager built-in role provides the required privileges to run setDefaultRWConcern.

设置全局默认写关注

以下操作将全局写关注设置为：

• w: 2

db.adminCommand({
  "setDefaultRWConcern" : 1,
  "defaultWriteConcern" : {
    "w" : 2
  }
})

该操作返回类似于以下内容的文档：

{
  "defaultWriteConcern" : {
   "w" : 2
  },
  "updateOpTime" : Timestamp(1586290895, 1),
  "updateWallClockTime" : ISODate("2020-04-07T20:21:41.849Z"),
  "localUpdateWallClockTime" : ISODate("2020-04-07T20:21:41.862Z"),
  "ok" : 1,
  "$clusterTime" : { ... }
  "operationTime" : Timestamp(1586290925, 1)
}

设置全局默认读关注

以下操作将全局读关注设置为 "majority"：

db.adminCommand({
  "setDefaultRWConcern" : 1,
  "defaultReadConcern" : { "level" : "majority" }
})

该操作返回类似于以下内容的文档：

{
  "defaultReadConcern" : {
    "level" : "majority"
  },
  "updateOpTime" : Timestamp(1586290895, 1),
  "updateWallClockTime" : ISODate("2020-04-07T20:21:41.849Z"),
  "localUpdateWallClockTime" : ISODate("2020-04-07T20:21:41.862Z"),
  "ok" : 1,
  "$clusterTime" : { ... }
  "operationTime" : Timestamp(1586290925, 1)
}

取消设置全局默认读关注和写关注

以下操作将全局默认读关注和写关注设置为：

• w: 2 写入安全机制

• level: "majority" 读关注。

db.adminCommand({
  "setDefaultRWConcern" : 1,
  "defaultWriteConcern" : {
    "w" : 2
  },
  "defaultReadConcern" : { "level" : "majority" }
})

该操作返回类似于以下内容的文档：

"defaultWriteConcern" : {
  "w" : 2
},
"defaultReadConcern" : {
  "level" : "majority"
}

设置全局默认读关注和写关注

您可以：

• 取消设置全局默认读关注。

• 仅当尚未设置全局默认写关注时，才能取消设置。

例如，假设全局默认读关注设置为 level: "majority"。要取消设置全局默认读关注，请使用空文档 {}：

db.adminCommand( {
   "setDefaultRWConcern" : 1,
   "defaultReadConcern" : {}
} )

该操作返回一个文档，指明操作成功：

{
   defaultReadConcern: { level: 'local' },
   defaultWriteConcern: { w: 2, wtimeout: 0 },
   updateOpTime: Timestamp({ t: 1656696934, i: 1 }),
   updateWallClockTime: ISODate("2022-07-01T17:35:40.578Z"),
   defaultWriteConcernSource: 'global',
   defaultReadConcernSource: 'implicit',
   localUpdateWallClockTime: ISODate("2022-07-01T17:35:40.578Z"),
   ok: 1,
   '$clusterTime': {
      ...
   },
   operationTime: Timestamp({ t: 1656632593, i: 1 })
}

仅当尚未设置全局默认写关注时才能取消设置。

要取消设置全局默认写关注，请使用空文档 {}：

db.adminCommand( {
   "setDefaultRWConcern" : 1,
   "defaultWriteConcern" : {}
} )

如果全局默认写关注为：

• 取消设置，操作成功。

• 已设置，操作将返回以下错误。

MongoServerError: The global default write concern cannot be unset
once it is set.