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Subject: Re: Some comments on definition of operation/group and action


Two points I tried to make here
1) if once an operation commits/completes its data is accessible to other operations and transactions thus a backward recovery might not be possible - we cannot guarantee that. In order to guarantee a reversible operation one definitely needs more rigorous rules and mechanisms to prevent any operation to violate that (the constraint). We need an entity, something like a gatekeeper of the group operations and groups defined consistency constrains.
2) Sine a backward recovery (thru compensation) is not always possible one may try forward recovery (thru some compensation and some contingency operations) which makes the group like action defined in the requirements doc. I belive at action level we have both forward and backward operations.
>>>>
I'd like to see us considering the use of nested transactions for groups.
Why applications responsibility? There should be some ways to do some level of check thru some entities that are part of BTP. For example if the structure of transactions known one may check transactional dependencies between transactions to prevent conflicting operations, specially if they are ACID transactions. Letting these checks build/designed by application will surely create applications where cascading rollbacks and compensations are common and creating a lot of problems.
>>>>
In a loosely coupled environment like the Web this is going to be an almost intractable problem. It's similar in problem to distributed deadlock-detection, and that's still an open area of research work! For a start you'd require that the entities used within a transaction are known before you begin, which is certainly not always going to be the case.
 
Mark.
 
----------------------------------------------
Dr. Mark Little (mark@arjuna.com)
Transactions Architect, HP Arjuna Labs
Phone +44 191 2064538
Fax   +44 191 2064203
 
 


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