Re: Boxcarring and its implications (was Re: Open-top coordinators andprotocol)

[Alastair Green <alastair.green@choreology.com>]

>
> Obviously you have to understand the message if you receive it. However,
> what I am against is a protocol that only works with piggybacking of
> messages. This is an optimisation that may well work in some situations but
> not in others, and as such, if you can't understand the compound message the
> protocol should still work (albeit with more message exchange).

Are you saying that implicit context propagation should be optional? (Receiver
does not have to understand this?)

>
> This would work, as long as that actor is not mandated. There will be
> communications protocols/distributed infrastructures that simply do not let
> you do this optimisation, and we should not remove ourselves from those
> arenas by mandating boxcarring.

Don't buy this. If something can receive a message, and the receipt can be
associated with computation, then boxcars can be unloaded and messages
forwarded. The carrier protocol itself may not be capable, that doesn't end the
matter. Analogy, that I have already raised some weeks ago: if a protocol
doesn't support headers or contexts, then one can simulate the effect by a BTP
envelope or array structure, which can be carried over any carrier.

> However, if it's optional, then that's
> great. Application-level negotiation can be conducted between end-points to
> figure out whether or not they are going to us boxcarring, and this could
> occur dynamically with the first message exchange, so no-one sees it anyway.

I'm not convinced this is the way to go. I would prefer to see boxcarring as an
mandatory interoperable feature.

Alastair

>
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