Please add documentation of JBPAPP-2257 to the clustering section of the Administration and Configuration guide. Should go in the HTTP chapter[1]. After the "Using FIELD-level replication" seems like a good spot.

Source material for the documentation can be found at http://www.jboss.org/community/wiki/HAWebSessionsviaDatabasePersistence.

[1] http://www.redhat.com/docs/en-US/JBoss_Enterprise_Application_Platform/5.0.1/html/Administration_And_Configuration_Guide/clustering-http.html