Profiling has shown the code in the enhancer generated pcCopyKeyFields(To/From)ObjectId to be costly when using id classes with an entity that uses field access and has non-public fields. Without public fields, reflection is used to move the values from the parent entity to the id class. This also involves a costly temporary access switch.
I have a fix that interrogates the id class for a public constructor and uses that constructor (instead of costly reflection) during the copy operation. It only works for certain IdClass and entity combinations. IdClasses must have a trivial public constructor with parameters that match those of the id fields. Trivial = the constructor can only do direct field assignments from the parameter values to the id class values. No conversion can take place. The constructor can have other logic, but the assignments must be direct. The entity ids cannot be derived from other identities. If these conditions are not met, the enhancer falls back to using reflection.
Since this change could result in an application behavior change (the provider calling a new constructor) it is gated by the openjpa.OptimizeIdCopy property, with the default being false.