setDefaultRWConcern

Replica Sets

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.

Sharded Clusters

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.

When an application issues an operation against the mongos without explicitly specifying a read or write concern setting, the mongos applies the corresponding global default setting.

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

Access Control

For replica sets or sharded clusters enforcing Authentication, setDefaultRWConcern requires that the authenticated user have the setDefaultRWConcern privilege action.

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

Set Global Default Write Concern

The following operation sets the global write concern to the following:

• w: 2

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

The operation returns a document similar to the following:

{
  "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)
}

Set Global Default Read Concern

The following operation sets the global read concern to "majority":

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

The operation returns a document similar to the following:

{
  "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)
}

Set Global Default Read and Write Concern

The following operation sets the global default read and write concern to the following:

• w: 2 write concern

• level: "majority" read concern.

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

The operation returns a document similar to the following:

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

Unset Global Default Read and Write Concern

You can:

• Unset the global default read concern.

• Only unset the global default write concern if you haven't already set it.

For example, assume the global default read concern is set to level: "majority". To unset the global default read concern, use an empty document {}:

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

The operation returns a document that indicates the operation was successful:

{
   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 })
}

You can only unset the global default write concern if you haven't already set it.

To unset the global default write concern, use an empty document {}:

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

If the global default write concern is:

• Unset, the operation succeeds.

• Already set, the operation returns the following error.

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