interposition

Hopefully this is all implicit in what everyone's assuming, but to try to 
clarify what I mean by interposition and participation.

 

We all seem to be agreed that a participant takes part in the termination 
protocol. However, a participant can't simply do sub-coordination: that's 
different functionality. For example, a book purchasing participant can't 
suddenly decide to sub-coordinate on behalf of other participants it may talk 
to. The functionality required for sub-coordination is different from "straight 
forward" participation. A sub-coordinator needs to be a proxy for the 
coordinator, and this has implications on recovery and its interface (e.g., it 
now has to have the enlist etc. interface, which a "normal" participant doesn't 
need to have), as well as context propagation.

 

Therefore, being a subcoordinator is:

 

(i) a conscious choice of the implementer to provide that kind of 
functionality.

 

(ii) a conscious choice of the application/participant to use that 
functionality.

 

If a participant has the sub-coordinator interface and functionality then 
you can (essentially) flick a switch and enable/disable that functionality. 
However, if it doesn't then you can't. I am in no way saying that BTP should 
mandate that all participants should be able to behave as subcoordinators. It's 
a choice, and we should allow it. My original email of days ago was produced 
because it appeared as though we were mandating the opposite, i.e., that no 
participant could behave as a subcoordinator, and all participants, whether 
directly or indirectly communicated with, had to register with the root (and 
only) coordinator.

 

Mark.

 

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: Dr. Mark Little, Architect (Transactions), HP Arjuna Labs
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