Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!wuarchive!mit-eddie!uw-beaver!cornell!ken From: ken@CS.Cornell.EDU (Ken Birman) Newsgroups: comp.sys.isis Subject: Re: looking for real-life examples of isis-groups Keywords: overlapping groups, semantics, causality Message-ID: <1991May12.174040.24185@cs.cornell.edu> Date: 12 May 91 17:40:40 GMT References: Sender: news@cs.cornell.edu (USENET news user) Distribution: comp Organization: Cornell Univ. CS Dept, Ithaca NY 14853 Lines: 33 Nntp-Posting-Host: fafnir.cs.cornell.edu In article dalia@SHUM.HUJI.AC.IL (Dalia Malki) writes: >This complication arises only if there is causality dependence among them... Two clarifications: First, I want to point people to the more complete discussion of this issue in the paper that I recently wrote with Robert Cooper and Barry Gleeson (Programming with process groups: Group and multicast semantics). Also, readers may want to keep in mind that if they use the ISIS tools in applications that contain multiple groups, they "automatically" need the causal property. This is because the tools are quite asynchronous (i.e. they let processes get quite far out of sync with one another), esp. replicated data update using cbcast or abcast with no replies, and the coordinator cohort tool. In these cases, if you have multiple groups, the ISIS tools themselves would be buggy if we didn't preserve causality over group boundaries. For example, two replicated writes might be seen in inconsistent orders by members of a group or a coordinator-cohort application might simply hang. The reason I wanted to make this point is that, in ISIS, the causal guarantee can be used explicitly, but also enters in an implicit way, in that it lets you do things that are very asynchronous without being aware that you have done so -- i.e. without worrying about race conditions, etc. Thus, if you use these sorts of tools and multiple groups, you may want to respond to Dalia by describing your application, even if you are unclear on whether the causal issue arises in your case. -- Kenneth P. Birman E-mail: ken@cs.cornell.edu 4105 Upson Hall, Dept. of Computer Science TEL: 607 255-9199 (office) Cornell University Ithaca, NY 14853 (USA) FAX: 607 255-4428