The Trace mechanism is inflexible and inefficient - specifically it doesn't enable custom tracing around a node.

What it won't let me do:
I want to be able to correlate the "out" trace with the "in" trace, in one database row without commiting the row until the route has completed.
This requires a JPA transaction to exist around each of the nodes that are called.
I'm finding that the transaction has ended by the time of the "out" trace.

Inefficiencies:
1. It causes the construction of the new Exchange object and a bunch of String objects that I don't want.
2. It causes the invocation of a new route, that is unnecessary.

I think it would be better to:
1. Pass the class to use as the TraceInterceptor into Tracer.
2. Break the existing TraceInterceptor into two, a base class that tracks the RouteNodes and a subclass that implements traceExchange.
3. Change traceExchange so that it returns an Object and pass that Object in to the call to traceExchange for "out" traces.
4. Give the Tracer a payload object that can be used to pass information to the TraceInterceptor.
5. Change the various trace* functions to take in and return a payload Object.
Custom users could then dervice from TraceInterceptor and override the trace* functions as necessary (probably just traceExchange).

I'm working on a patch.