On Fri, May 06, 2005 at 10:14:38AM -0600, Patrick Walsh wrote:
> 	I was under the impression that coda used multicast to broadcast
> updates, but I'm not sure this is happening.  I noticed there is a
> command: vutil -mc 1, that is supposed to turn it on.  Is this stable?
> Where is it used?  When a client does a write, does it multicast it to
> the entire realm (if possible)?  Or is it just when a server is sending
> updates to multiple replicas?  Or can a server use multicast to notify
> all nearby clients of a change to a file?

It used to use some old form of multicast, the VSGDB group numbers would
match the multicast ip addresses. But that hasn't been used for a long
time and most of the needed code has probably disappeared by now.

We do use 'multirpc', where we send out a batch of requests at a time,
and then wait for the responses. This doesn't save any bandwidth, but
does save a lot in latency compared to normal RPC, where each message
would be an individual request/reponse.

> 	There seem to be plenty of places, particularly in the RPC2
> documentation, that talk about multicast, but none that seem to say
> exactly how it is used or when.  

I though most places talked about MultiRPC and not multicast, but then
again, it has been a while since I last looked at the RPC2 documentation.

> 	If it isn't set up to be used by default, I'd be curious to know why
> this is the case.  Was it unreliable? 

Maybe because it really only worked on a local area network. I'm not
sure if it has been used or if it was just an experiment.

Jan