When loading the default fetch group fields into a PersistenceCapable object that is not involved in a transaction, Kodo JDO will set the jdoFlags field of the object to READ_OK. This means that subsequent read operations will not be mediated by the StateManager, reducing the number of method calls and therefore increasing performance.

When you modify a default fetch group field in a PersistenceCapable object that is involved in a transaction, Kodo JDO sets the jdoFlags field of the object to READ_WRITE_OK. This means that subsequent write operations to fields in the default fetch group will not perform checks against the data store, or otherwise access the StateManager. Additionally, when writing the data back out to the data store, all fields in the default fetch group will be written. This is because Kodo JDO does not intercept writes to fields in the default fetch group after they have been loaded, so it is impossible to know which of these fields have been modified. This may result in undesirable data store behavior, including unexpected firing of triggers. Explicitly removing elements from the default fetch group will resolve this.

See section 20.9.3 of the JDO specification for more details about this behavior.