If you configure a single instance of Java Message Queue Broker and as single instance of Berkeley Database to provide session failover for your deployment, no session data replication is possible. If either Message Queue Broker or Berkeley Database fails, then all the stored user sessions are lost. The OpenSSO Enterprise server would operate as if session failover was not configured.
A good practice is to use two instances of Message Queue Broker configured with two instances of Berkeley Database. User sessions are replicated among the Berkeley Database instances. This dual-host configuration is for failover purposes and not for load sharing. Adding more Message Queue Broker instances and Berkeley Database instances does not increase processing capacity. Adding more instances actually reduces the overall session failover processing capacity due to the extra data replication overhead.
The Java Message Queue Broker and Berkeley Database pair should be configured in an active-standby mode so that at any given time only one of the pair is up and running.
The Java Message Queue Broker and Berkeley Database pair on the backup host is be used only for failover purposes.
When the primary Java Message Queue Broker and Berkeley Database pair fail, other pair on the backup host can be started to provide uninterrupted session service.