dalia@SHUM.HUJI.AC.IL (Dalia Malki) (05/16/91)
According to some of the replies I received, I feel I should re-post my question and clarify it: According to the TR 'Lightweight Causal and Atomic Group Multicast' by Birman, Schiper and Stephenson, causal order is preserved among different groups if they intersect. Thus, if there is a "chain" of intersecting groups, messages in any one of the groups needs to contain information about the whole chain. (The authors further show that a process needs to send information only about all the groups in the 2-connected components it belongs to. I am not sure whether this situation is recognized in practice, or how complicated is the detection). This seems like a great complication to me, one that may be intolerable in a system of hundreds of groups. My question is as follows: Although I understand the theoretical need for causal order preserving among intersecting groups, I wonder whether such situations arise in real life applications. (here I am not looking for the diagram 'a and b belong to A, ...', but for REAL applications and their structure). In other words: Show me an example where there are two or more intersecting groups, there is a need to preserve causal order among them, but it does not make sense to unify all such "logically-connected" groups into one big (happy) group. Either that, or they are completely independent, in which case the relative order of messages should not be kept. Please send replies directly to me, and I will make a summary for the news group eventually. Thanks, - Dalia Malki ------------------------------------------------------------ E-mail: dalia@humus.huji.ac.il Dalia Malki Computer Science dept., The Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904 Israel