[Telepathy] Properties of D-Bus MUC tubes

Sjoerd Simons sjoerd at luon.net
Fri Oct 9 01:54:23 PDT 2009


On Sat, Sep 26, 2009 at 08:00:57PM +0100, Simon McVittie wrote:
> I consider this to be an invariant of Tubes - clients that cannot guarantee
> that they have received every message should signal it as disconnection from
> the tube, dropping messages if necessary to avoid violating causal ordering.
> 
> Clique does this correctly - if it takes too long to fetch the old messages
> necessary to provide causal ordering, Salut will leave the Clique room,
> dropping the unprocessed messages.

Slight correction here. In Clique if a node fails to get an old message
it will re-establish the membership of the group, with only those members it
can still communicate directly or indirectly with [0]. In practise that means
that when this happens you will end up with a smaller group (which can have
just you in it).

The practical side-effect of this is that in Clique groups can split and later
merge again (similar to a netsplit on IRC)! Which means that if you're a fully
pedantically correct tubes application you can't assume that new members start
from scratch.

  Sjoerd

0: For the mathematicians under us, in Clique communication is a transitive
   property. If node A can communicate with node B and B can communicate with
   node C, then A can communicate with C regardless of what the underlying
   network does.

-- 
If you find a solution and become attached to it, the solution may become
your next problem.


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