ken@gvax.cs.cornell.edu (Ken Birman) (02/16/91)
A transactional reader of my last posting pointed out that the figure 12 shouldn't actually surprise people. An ISIS multicast is roughly comparable in "strength" to an atomic replicated database update, and those would cost "3*n" RPC's to do one update on n copies too: n to do the update and get confirmation that the copies were up, and then 2*n for the 2-phase commit. Of course, the database system would normally be using persistent memory, so the 2-phase commit stage will be more costly than anything ISIS needs to do. The person who pointed this our (anonymously) argues that things like ISIS belong "over" systems like ARGUS or CAMELOT. Actually, I think the costs are lighter in ISIS because we don't worry about disk IO and log forcing, and that if anything, systems that do transactional replicated data should sit over ISIS. Anyhow, ISIS is probably more like a database system then an RPC system. Your manager may not see the point, but in fact it is remarkable that we may be able to run as fast as RPC in most situations within the near future! -- Ken (Thanks to my anonymous correspondent. Why not post directly to the group?)