[ejabberd] How do conference rooms scale?

Heiner Wolf wolf at bluehands.de
Wed May 10 19:33:43 MSD 2006


the scalability issue comes up from time to time.

Yes, rooms with really many users would be interesting. MUC in
ejabberd seems to be not clusterable. I wonder why, because isn't it
Erlang's unique selling proposition, that things you program are
clusterable. Obviously, I don't know enough about Erlang to judge

On the other hand, ejabberd's MUC does not need to be clusterable,
because if there are so many users in one room that you need a cluster
of servers, then your rooms presence list would be way to large. In
other words, the protocol is the first to break.

Even 1000 in a room is a problem, because traffic in the MUC protocol
scales with n^2 of the number of participants. We need another
protocol before we need a clusterable implementation.

You should check the jabber.org list archives. We discussed ideas
about how to extend the MUC protocol for many users. The simplest idea
being not to announce any participant individually, but to send
summaries and let the client fetch the list if it needs it. This list
fetching however has the same traffic issues and would be done in
smart ways with paging, filtering, etc.

My impression is that MUC in ejabberd

On 5/9/06, Peter Saint-Andre <stpeter at jabber.org> wrote:
> I've had some discussions with some people who are interested in very
> large conference rooms distributed across services, but the protocols
> for that kind of mirroring or sharing have not yet been worked out.
> Peter
> On Tue, May 09, 2006 at 07:39:54PM +0100, Joel Reymont wrote:
> > Paul,
> >
> > You are assuming that all the users would be visible in the
> > conference room. I'm thinking of a bunch of MUC servers all having
> > the same JID and implementing the same conference room. You can have
> > a manageable number of users in each and messages from other servers
> > could come from a hidden user or admin or something like that.
> >
> > I'm not trying to implement a chat per se, I'm just piggybacking on
> > the XMPP protocol.
> >
> > On May 9, 2006, at 7:27 PM, Paul Vixie wrote:
> >
> > >>I want to implement "conference rooms" with hundreds of thousands
> > >>of  users
> > >>in them where very few would be "typing" and most would be
> > >>listening.
> > >
> > >just downloading the roster would take a megabyte or more per
> > >user.  this
> > >can't scale for reasons unrelated to ejabberd.
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