Wednesday, September 30, 2009

SOA transactions and reservations

Arnon and I have spoken about SOA transactions in the past, so it was interesting to read his latest article (book chapter?)

It's a nice paper to read, though I disagree with several things he has to say. For instance, I don't like the term "semi-state" or that somehow the use of compensations increases the service's contract footprint. Furthermore compensations (not just Sagas) don't have to use locks. As we kept saying during BTP development, that's a back-end service implementation choice that doesn't have to be exposed to users.

The reservation pattern is important and it's something that's been described several times before, particularly in the area of specific implementation approaches such as BTP, WS-TX and WS-CAF. So although I haven't seen Arnon's book, I can appreciate why he's including this chapter and I liked the discussions on possible risks when using the pattern. However, it would be good to see the aforementioned approaches referenced, particularly since there's a discussion about how you could do this with EJB3.

But the one thing (the elephant in the room) that is glossed over in the discussion (which isn't if you read about the reservation approach elsewhere) is that there's something in the environment directing the flow of interactions across many services. If it looks like a coordinator, behaves like a coordinator and smells like a coordinator then chances are it's a coordinator.

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