What does setting SubclassFetchMode (Kodo OpenJPA) actually do?

Question

What does setting SubClassFetchMode e.g. to EAGER_PARALLEL actually do?

Why would one want a subclass to have a different FetchMode?

The implementation spec for KODO and OpenJPA is notoriously bad and I can't figure it out.

Answer 1

From http://download.oracle.com/docs/cd/E15523_01/apirefs.1111/e13946/ref_guide_professional_eager.html

"Setting your subclass fetch mode to parallel affects table-per-class and vertical inheritance hierarchies. Under parallel mode, Kodo issues separate selects for each subclass in a table-per-class inheritance hierarchy, rather than UNIONing all subclass tables together as in join mode. This applies to any operation on a table-per-class base class: query, by-id lookup, or relation traversal."