setDefaultRWConcern
Definition
setDefaultRWConcern
The
setDefaultRWConcern
administrative command sets the global default read or write concern configuration for a replica set or sharded cluster.setDefaultRWConcern
must be run against theadmin
database.For replica sets, issue the
setDefaultRWConcern
command on the primarymongod
.For sharded clusters, issue the
setDefaultRWConcern
on amongos
.
Compatibility
This command is available in deployments hosted in the following environments:
MongoDB Atlas: The fully managed service for MongoDB deployments in the cloud
Note
This command is supported in all MongoDB Atlas clusters. For information on Atlas support for all commands, see Unsupported Commands.
MongoDB Enterprise: The subscription-based, self-managed version of MongoDB
MongoDB Community: The source-available, free-to-use, and self-managed version of MongoDB
Syntax
The command has the following syntax:
db.adminCommand( { setDefaultRWConcern : 1, defaultReadConcern: { <read concern> }, defaultWriteConcern: { <write concern> }, writeConcern: { <write concern> }, comment: <any> } )
Command Fields
The command takes the following fields:
Field | Type | Description |
---|---|---|
| Set to | |
| Document containing the global read concern configuration. Specify a valid read concern object.
Omit this document to leave the current global read concern
unmodified. If omitted, | |
| Document containing the global default write concern configuration.
Omit this document to leave the current global write concern
unmodified. If omitted, | |
object | Optional. A document that specifies the
write concern to be used by the
If omitted, | |
| any | Optional. A user-provided comment to attach to this command. Once set, this comment appears alongside records of this command in the following locations:
A comment can be any valid BSON type (string, integer, object, array, etc). |
setDefaultRWConcern
returns an object that contains the
currently configured global default read and write concern. See
getDefaultRWConcern
for more complete documentation on
the returned fields.
Behavior
Note
Requires featureCompatibilityVersion 4.4+
Each mongod
in the replica set or sharded cluster
must have featureCompatibilityVersion set to
at least 4.4
to use setDefaultRWConcern
.
Starting in MongoDB 5.0, once the Cluster Wide Write Concern (CWWC)
is set via the setDefaultRWConcern
command the write
concern cannot be unset.
MongoDB only applies the global default read or write concern to operations which do not explicitly specify a read or write concern.
If MongoDB applies the global default read or write concern to an operation, that operation behaves as if that read or write concern were explicitly specified by the issuing client.
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.
Important
setDefaultRWConcern
requires
featureCompatibilityVersion 4.4+
. If you
downgrade your deployment's featureCompatibilityVersion from 4.4
to 4.2
, all cluster-wide read and write
concern defaults are lost, but mongos
instances may
continue applying the defaults for up to 30 seconds.
Sharding Administrative Commands Override Write Concern Settings
Sharding administrative commands that perform write operations on the
config server, such as the
enableSharding
or addShard
commands,
have specific behavior with global default write concern settings:
The commands use
"majority"
regardless of the configured global default write concern.The commands use a minimum wtimeout of
60000
. The commands only use the global default write concernwtimeout
if it is greater than60000
.
Access Control
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
.
Example
Set Global Default Write Concern
The following operation sets the global write concern to the following:
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 concernlevel: "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.