33.2.3. Case #2: Surviving HTTP session replication

The HTTP Session is used when passivating stateful session beans, but in clustered environments that have enabled session replication, the HTTP Session can also be passivated. Since the persistence manager cannot be serialized, passivating the HTTP Session would normally involve destroying the persistence manager.

When an entity instance is first placed into a conversation, Seam embeds the instance in a wrapper that contains information about reassociating the instance with the persistence manager post-serialization. When the application changes nodes (when a server fails, for instance), Seam's MEI reconstructs the persistence context. The persistence context is reconstructed from the database, so pending changes to the instance are lost. However, Seam's optimistic locking ensures that, where files have changed, only the most recent changes are accepted where multiple versions of an instance occur.