Goal

This is test project in order to evaluate different approaches that lead to a dynamic OModel for Apache ODE.

Problem Statement

In Apache ODE, BPEL processes are compiled to an in-memory object model (OModel). This model is being used during runtime, the runtime execution state maintains references to the OModel. In order to keep the memory footprint manageable, the OModel is loaded (hydration) and unloaded (dehydration) on demand. Thus, there are certain requirements to be fulfilled by the OModel:

1. OModel must be evolvable. OModel graph instances may live longer than a certain OModel version. It must be possible that newer OModel versions can still load old OModel serializations.

2. Low memory footprint. The OModel is an object graph, each object should use as little memory as possible.

3. Fast field access. Since the OModel is read frequently, read access should be as fast as possible.

4. Fast loading. The OModel must be serialized and unserialized as fast as possible. Also, the file size should be as small as possible (no compression, just focus in IO and performance).

The OModel in its current form uses public fields and Java's built-in serialization. This leads to massive problems with binary compatibility when the OModel structure evolves.

Considerations

• Requirement 1 is the most important issue. Using a Map as the underlying data structure makes the content structure of a class changeable without affecting the class structure itself. Using a Map, however, can negatively effect requirement 2 and 3.

• Requirement 2+3: TODO: Are there alternatives to Maps that still satisfy requirement 1? Which Map implementation would serve best?

• Requirement 4: According to a JVM serializers benchmark, Jackson is a good candiate for this refactoring effort. It is fast, provides a data mapping to basic Java types, can deal with object graphds (ObjectIdentity, since 2.0) and provides a fast and small binary serialization (Smile).