If your implementation uses session federation (see Session Federation Overview in the ATG Installation and Configuration Guide) consider the following situation: a site visitor triggers a scenario by logging into server A and then follows a link to server B. If session federation is enabled, the person will have a profile object on both servers. If another scenario event (for example, a timer event) occurs, both servers will try to advance the visitor to the next state in a scenario state machine. This behavior could cause conflict or unexpected results.

If you use session federation on servers that process scenarios, you can prevent this type of conflict by setting the SQL repository cache mode to locked for all scenario tables. See the previous section, Configuring SQL Repository Caching for Scenarios, for more information.