Schema update fails when upgrading from Retain 4.7.0.1 to 4.9.1

Customers that are running a non-Maria DB for their Retain system cannot upgrade directly from 4.7.0.1 to 4.9.1.

The RetainServer log will show:

11:02:38, 164[StartupThreadProcess] [FATAL] StandardStartupListener: PROCESSINFO checkDBSchema SERIOUS ISSUE :==================================== ATTENTION =========================================================================
**** The Message DB Schema needs updating, hence many operations will be disabled. You must log in as Admin to resolve this ****
==================================== ATTENTION =========================================================================

12:06:22, 500[UpdatingSchemaThread] [ERROR] ServerErrorHandlerStrategy: reportError: fixSchema :: com.gwava.exceptions.StartupError.fixSchema:387 :: EXCEPTION : com.gwava.cfg.dao.RetainMessageDataAccessException: Wrong Database Engine detected: unknown com.gwava.cfg.dao.RetainMessageDataAccessException: Wrong Database Engine detected: unknown
    at com.gwava.hibernate.HibernateUtil.validateSchema(HibernateUtil.java:311)

If the upgrade to 4.9.1 has not been attempted, the recommendation would be to upgrade to Retain 4.8.1 first, and then upgrade to 4.9.1.

If the upgrade to 4.9.1 has already been attempted, then there are two options to resolve this:

1) Contact Support and obtain the patch for Defect RET-14142. Apply this patch and reset the Schema version by following TID 7023406

2) Upgrade to Retain 4.9.2 which contains the fix to handle the schema update process.