Re: [bt-spec] BTP Issue 99 : PREPARE_INFERIORS andFAULT(InvalidInferior)

[Mark Little <mark_little@hp.com>]

 

That's basically reasonable, but there is no need to impose it on all implmentations. For safety, in the confirm case, the implementation must check before it confirms, but there is no similar requirement in the other cases. In fact, the other two are really just packaging of "prepare-one-inferior" and "cancel-one-inferior" allowing multiple targets.

For CANCEL I don't think we need to check. However, for PREPARE I'm not persuaded yet. The business logic has decided that it wants to prepare a set of inferiors and has assembled that set, though one of them is invalid. Now maybe we aught to be asking how this is possible, but if we ignore that for now, I think it is reasonable to assume that the prepare set has been assembled for some specific reason. If I scr*w up when making that set it may well affect my choice of the set in the first place, i.e., if I know that id 1234 is invalid then I may very well not have assembled it *and* 6789 5678 ... into the prepare set in the first place - my prepare set may very well be completely different.

 

Now, if I can't check until I've sent the PREPARE_INFERIORS message and when that tells me I scr*wed up all of the other inferiors are prepared, I've got to go and cancel them and then do something else. I'd prefer the ability to know that nothing happened in the first place (it's as though I didn't send the PREPARE_INFERIORS and invoked some CHECK_INFERIORS message instead).

 

 But CONFIRM_TRANSACTION is different, as it defines a new set of inferiors that must confirm together or not at all.  An implementation could choose to implement the prepare and cancel as strictly sequential, just working through the list. This won't work for confrim, whcih must check they are prepared first.

 

Mark.

 

----------------------------------------------
Dr. Mark Little, Distinguished Engineer,
Transactions Architect, HP Arjuna Labs
Email: mark_little@hp.com
Phone: +44 191 2606216
Fax  : +44 191 2606250