Re: verbatim notes from London bt models meeting

[Mark Little <mcl@arjuna.com>]

> The mechanisms used would be considered internal to the service. But those
> in London wanted the first to be possible.
>
> I think this effectively means we are looking at a two-phase exchange (I
> think this was the assumption of those physically at the meeting, though I
> don't remember it being stated quite that directly). But a two-phase
> exchange (meaning just "can you do your part ?", "yes", "then let it be
> done"/"dont do it after all") is inevitable if we are to have any level of
> atomicity or consistent application of operations anyway.

Agreed. And the argument that you can't guarantee ACID because the
participants may simply release locks and generate heuristics if the outcome
is "slow" is subjective anyway since "slow" can be seconds and not just
hours, i.e., from that argument you can never guarantee ACID properties. I
think that if an application required ACID properties for its business
transaction then we should not prevent it from happening with this protocol.

> Separately - most of the timelimits discussion was on the possibility of
the
> compensation itself having a limit, as in reservation situations, where
the
> reservation is held for some period and then service will decide for you
if
> you haven't got back to them.  I don't think this can be avoided - it's
just
> the way some people will do business.  If the timeout is hit, then it does
> rather break the model (it's similar to heuristic decisions, but at least
> there can be prior warning in this case).

I would still prefer to see compensations as simple another "cohesion" that
is fired off due to a specific outcome. If this cohesion can only be invoked
within the next X hours or it makes no sense, say, then that's part of the
business logic.

Mark.

----------------------------------------------
Dr. Mark Little (mark@arjuna.com)
Transactions Architect, HP Arjuna Labs
Phone +44 191 2064538
Fax   +44 191 2064203