Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!newstop!exodus!noam.Eng.Sun.COM!jyl
From: jyl@noam.Eng.Sun.COM (Jacob Levy)
Newsgroups: comp.sys.isis
Subject: Tool for getting single answer back from broadcast
Summary: Broadcasting is wasteful sometimes
Message-ID: <6934@exodus.Eng.Sun.COM>
Date: 30 Jan 91 04:18:20 GMT
Sender: news@exodus.Eng.Sun.COM
Organization: Sun Microsystems, Mt. View, Ca.
Lines: 20

Sometimes you do a broadcast and want to get exactly one answer
back. The standard example is retrieval of replicated data. In
this case it is OK to wait only for one answer since the other
ones are redundant. ISIS currently still broadcasts to all
members of the group.

My question is: would it be possible to have a tool which, given
a PG address, would try getting the answer from each process in
turn, only attempting to broadcast to the next one after the
current one hasn't answered?

The delay caused by the use of such a tool in the general case
where no failures occur should be the same as that of
broadcasting to the entire group, since we'd be waiting for the
first answer anyway. There are probably a lot of tricky issues
wrt maintaining causality, e.g. those processes that did not
receive the broadcast must still behave as if they are in the
causal path of the broadcast.

--JYL