setDefaultRWConcern¶

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Definition
Behavior
Example

Definition¶

New in version 4.4.

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 the admin database.

For replica sets, issue the setDefaultRWConcern command on the primary mongod.
For sharded clusters, issue the setDefaultRWConcern on a mongos.

setDefaultRWConcern has the following form:

copy

db.adminCommand(
  {
    setDefaultRWConcern : 1,
    defaultReadConcern: { <read concern> },
    defaultWriteConcern: { <write concern> },
    writeConcern: { <write concern> },
    comment: <any>
  }
)

setDefaultRWConcern has the following fields:

Field	Type	Description
setDefaultRWConcern	`int`	Set to `1`.
defaultReadConcern	`object`	Document containing the global read concern configuration. Specify a valid read concern object. `setDefaultRWConcern` supports the following subset of level: `"local"` `"available"` `"majority"` To unset the currently configured default read concern, specify an empty document `{}`. `setDefaultRWConcern` only supports the `levels` read concern setting. You cannot specify any other read concern setting in the default read concern. Omit this document to leave the current global read concern unmodified. If omitted, `setDefaultRWConcern` must specify defaultWriteConcern.
defaultWriteConcern	`object`	Document containing the global default write concern configuration. For the write concern w setting, `setDefaultRWConcern` supports all write concern values except `w : 0`. For the write concern wtimeout setting, `setDefaultRWConcern` defaults to `0` if the setting is omitted. Operations block until the requested write concern is met. If specifying a global default `wtimeout`, ensure the value is large enough to allow write operations to achieve the requested write concern. To unset the currently configured write concern, specify an empty document `{}`. Omit this document to leave the current global write concern unmodified. If omitted, `setDefaultRWConcern` must specify defaultReadConcern.
writeConcern	object	Optional. A document that specifies the write concern to be used by the `setDefaultRWConcern` command itself. If omitted, `setDefaultRWConcern` uses the previously set global default write concern if one was configured.
`comment`	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: mongod log messages, in the `attr.command.cursor.comment` field. Database profiler output, in the `command.comment` field. `currentOp` output, in the `command.comment` field. A comment can be any valid BSON type (string, integer, object, array, etc). New in version 4.4.

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¶

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.

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 concern wtimeout if it is greater than 60000.

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.

Example¶

Set Global Default Write Concern¶

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

w: "majority"

copy

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

The operation returns a document similar to the following:

{
  "defaultWriteConcern" : {
   "w" : "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 Concern¶

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

copy

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: "majority" write concern
level: "majority" read concern.

copy

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

The operation returns a document similar to the following:

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

Unset Global Default Read and Write Concern¶

Consider a deployment with the following default read and write concern:

{
  "defaultWriteConcern" : {
    "w" : "majority"
  },
  "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)
}

The following operation unsets the global default read and write concern settings:

copy

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

The operation returns a document similar to the following:

{
  "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)
}

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