Description

An unhandled exception might be thrown while using MongoDB session state provider. The issue occurs when sending many simultaneous requests with the same session cookies. Sitecore XP instance tries to add the already existent session to the session database. It is not reproducible with other providers.

The following message can be found in the log records:

Exception: MongoDB.Driver.MongoDuplicateKeyException
Message: WriteConcern detected an error ''. (Response was { "ok" : 1, "code" : 11000, "err" : "E11000 duplicate key error collection: prod_TCFBank_com_local_session.sessions index: _id_ dup key: { : { s: \"4b139a8f-2458-4e68-9b03-b1ff5542db2b\", a: \"shared\" } }", "n" : NumberLong(0), "updatedExisting" : false }).
Source: MongoDB.Driver
  at Sitecore.Analytics.Pipelines.CommitSession.SubmitSession.Process(CommitSessionPipelineArgs args)
  ...

Solution

To resolve the issue, consider one of the following options:

• Upgrade Sitecore XP instance to 9.1 Initial Release or later (recommended).
• Download and install the patch compatible with the affected product version:
  https://github.com/SitecoreSupport/Sitecore.Support.155149/releases
  To get a solution for other releases, contact Sitecore Support.