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New in version 3.6.

The startSession command starts a new logical session for a sequence of operations.


In the mongo Shell, this command can also be run through the Mongo.startSession helper method.

Helper methods are convenient for mongo users, but they may not return the same level of information as database commands. In cases where the convenience is not needed or the additional return fields are required, use the database command.

startSession has the following syntax:

{ startSession: 1 }

To run startSession, use the db.runCommand( { <command> } ) method.

db.runCommand( { startSession: 1 } )


featureCompatibilityVersion must be 3.6 or greater to use the startSession command.


If the deployment enforces authentication/authorization, you must be authenticated to run the startSession command. The user who runs startSession owns the created session, and only that user can use the session.

If the deployment does not enforce authentication/authorization, a created session has no owner and can be used by any user on any connection. If the user authenticates and creates a session for a deployment that does not enforce authentication/authorization, the user owns the session. However, any user on any connection may use the session.

If the deployment transitions to auth without any downtime, any sessions without an owner cannot be used.


In addition to the status and operation time of the command, the startSession returns the following session specific information:

Field Type Description
id Document

The document that contains the 16-byte Universally Unique Identifier (UUID) portion of the session’s identifier.

id: { id: <UUID> }

The session’s identifier consists of this UUID concatenated with the hash of the authenticated user credentials.

timeoutMinutes number The amount of time, in minutes, since the last client use that a session remains active before expiring. By default, sessions have an expiration timeout of 30 minutes. To change the value, set the localLogicalSessionTimeoutMinutes parameter when starting up mongod. For replica sets and sharded clusters, you must specify the same value on every member.