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Subject: RE: [ws-tx] Issue 016: WS-C: ReplaceParticipant (and partly 007 too)
There is a general problem with assuming a recovered ws-tx entity can't get back to the endpoint it started on, so they have to tell the other side what the new EPR is. What happens if both side suffer such forced moves at the same time (not at all improbable, especially with long-running cases). If both sides fail, recover and come up on different endpoint addresses and there is no forwarding/fallback how will they ever find each other to complete the coordination protocol exchange ? Timeouts won't help if the relationship has already reached committing/prepared (in AT) or its equivalent. I think we must assume (and perhaps state explicitly) that we are assuming the EPR's exchanged on Register/RegisterResponse will continue to be valid for the lifetime of the Participant/Coordinator. It would still make sense to provide replacement (redirected) EPR's on by one means or another, but it needs to be ensured that a message sent to the original EPR will get there (though perhaps less efficiently than for the new EPR). In general, for EPRs this shouldn't be that onerous (certainly compared to middle-period CORBA, say) given the flexibility of dns, the possibility of local interpretation of the latter part of URI and the use of returning ReferenceParameters. There are other possibilities, but perhaps a seasonal analogy would be helpful. In sending our Christmas cards, there were some cases where we aren't sure whether the address we have is correct. If it isn't and the friends from the past have lost our address too, we are probably never going to be in contact again. But if the uncertainty is over my cousins' address, I know I can ask my aunt, and can ensure communication is maintained (assuming I want to, of course). Of course, for the long-lost friend, I could always try FriendsReunited. But I'm not sure of the feasibility of ParticipantsReunited. Peter
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