[Spread-users] multigroup_multicast

Paul Rubel prubel at bbn.com
Fri Jan 6 10:56:08 EST 2006


 I've been moving along with Spread. Before the new year I had some
questions about tweaking the timeouts to achieve sub-second detection
of failures. Lowering the parameters by a factor of 100 across the
board seems to have done the trick. I'm able to detect failure in ~.2
seconds using 12 daemons in 3 LANS.

Moving forward I'd like to use the multigroup_multicast calls. We were
looking for something like that and lo and behold it was already there,
thanks! I'm curious about the semantics when a message is sent to
multiple groups. Are the messages delivered as if all the members of
the groups were in one large group? In the multigroup case does the
notion of the individual groups mean anything? For example, could a
message be delivered to the members of one group while still trying to
reach agreement for members of another or does Spread wait until all
the members are in agreement as it would with a multicast to a single

On a related topic, when we have been measuring the detection time for
failures it seems like the first members of a segment, as listed in
the spread.conf, get the message before members further down in the
segment list. We're guessing this is caused by the first daemon listed
in each segment receiving the message/token first and then passing it
to the others, who receive (and therefore process) it later. Is the
correct that the ordering of daemons in the file affects the order in
which daemons get messages?

       thank you,

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