[zeromq-dev] ZMQ_MCAST_LOOP with PGM

[Steven McCoy]

On 26 July 2012 11:35, Ian Barber <ian.barber at gmail.com> wrote:

> On Thu, Jul 26, 2012 at 4:27 PM, Pierre Ynard <linkfanel at yahoo.fr> wrote:
>
> >
> > Anyway, is it safe to enable this option if I don't mind about
> > reliability?
> >
>
> I'm sure Steve can give a better answer, but basically multicast
> loopback just doesn't work very well at all, and causes a lot of
> confusion among people trying out PGM.
>
>
It can work well in a restricted environment, the disruptor team have shown
great performance with Java and multicast loop but with the PGM protocol
specifically there are problems and limitations that can break reliability.
>From OpenPGM viewpoint it is recommended to use IPC or ITC for localhost
broadcast, with ZeroMQ this is a simple as adding a new transport to the
socket.

PGM by default is a bi-direction transport and is the back channel that
gets broken with multiple nodes on the same host.  PGM can be made
uni-directional but ZeroMQ does not support this as it is a rather limited
use case.  PGM congestion control requires an additional back channel which
is impossible with multiple nodes on the same host.  It's a complicated
answer.

-- 
Steve-o
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