getDefaultRWConcern¶

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Definition
Behavior
Example

Definition¶

New in version 4.4.

getDefaultRWConcern¶

The getDefaultRWConcern administrative command retrieves the global default read or write concern settings.

For sharded clusters, issue the getDefaultRWConcern on a mongos.

getDefaultRWConcern must be run against the admin database. getDefaultRWConcern has the following form:

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db.adminCommand( { getDefaultRWConcern : 1 , inMemory: <boolean>, comment: <any> } )

getDefaultRWConcern has the following fields:

Field Type Description

getDefaultRWConcern

int

Set to 1.

inMemory

boolean

Optional.

Set to true to return the in-memory cached copy of the global default read or write concern settings. The instance uses the in-memory copy when applying the global defaults to an operation.

Set to false to return the on-disk copy of the deployment’s global default read or write concern. Defaults to false.

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.

getDefaultRWConcern output includes the following fields.

Field	Type	Description
defaultReadConcern	`object`	The global default read concern configuration. If this field is absent, the deployment has no global default read concern settings.
defaultWriteConcern	`object`	The global default write concern configuration. If this field is absent, the deployment has no global default write concern settings.
updateOpTime	Timestamp	The operation timestamp of when any global default read or write concern setting was last modified. Present if a default has ever been set for the cluster.
updateWallClockTime	Date	The wall clock date when an administrator last set the global default read or write concern. This value is informational and should not be used for any recency comparisons.
localUpdateWallClockTime	Date	The wall clock date when the `mongod` or `mongos` last updated its local copy of the global default read and write concern settings. This value is informational and should not be used for any recency comparisons.

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 getDefaultRWConcern. 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.

Replica Sets¶

You can issue getDefaultRWConcern against any data-bearing member of the replica set (i.e. not against an arbiter).

A secondary can return a ‘stale’ version of the global default settings if it has not yet replicated the latest changes from the primary.

Sharded Clusters¶

Issue the setDefaultRWConcern against a mongos in the cluster.

Each mongos periodically refreshes its local copy of the global default settings. A mongos can return a ‘stale’ version of the global default settings if it has not yet refreshed its local copy after a recent update to the global default settings or if it fetched its settings from a lagged config server secondary.

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

Access Control¶

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

The clusterManager or clusterMonitor built-in roles provides the required privileges to run getDefaultRWConcern.

Example¶

The following operation retrieves the currently configured global default read and write concern for the mongod.

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db.adminCommand({
  "getDefaultRWConcern": 1
})

The operation returns output similar to the following:

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{
  "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)
}

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