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  • Definition
  • Syntax
  • Behavior
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The startSession command starts a new logical session for a sequence of operations.


In mongosh, this command can also be run through the Mongo.startSession() helper method.

Helper methods are convenient for mongosh 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.

The command has the following syntax:

startSession: 1

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

startSession: 1


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


See also:

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.

A session can only be used with the MongoClient object that created the session. A single session cannot be used concurrently. Operations that use a single session must be run sequentially.

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


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.


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.




Administration Commands