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From: jfjr@mitre-bedford.ARPA (Jerome Freedman)
Newsgroups: comp.os.research
Subject: Re: Distributed simulation paradigms.
Message-ID: <3558@sdcsvax.UCSD.EDU>
Date: Fri, 31-Jul-87 08:38:18 EDT
Article-I.D.: sdcsvax.3558
Posted: Fri Jul 31 08:38:18 1987
Date-Received: Sun, 2-Aug-87 01:08:42 EDT
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Organization: The MITRE Corporation, Bedford, Mass.
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In article <3557@sdcsvax.UCSD.EDU> unni@sunset.sm.unisys.com (Unni Warrier) writes:
>Two of the more famous paradigms for distributed simulation are the
>Chandy-Misra scheme (CM) and the Jefferson time warp scheme (TW).  CM allows
>the distributed simulation to proceed till a deadlock and then have ways of
>detecting the deadlock, and resolving it.  A deadlock arises when each of the
>processes in a cycle is waiting for a message from the previous process.  TW
>allows the simulation to proceed and has a rollback mechanism for dealing
>with out-of-order timestamped messages.  Hence one question is:  has anyone
>used TW or CM in their distributed simulations? What are your experiences?
>
  
 We are in the process of building a simulation using the Chandy-Misra
paradigm for practical reasons. The big problem(s) with simulation,
especially one big enough to require a distributed implementation 
is validation (debugging). When you build such a thing you would
surely include all types, flavors etc of tracing/dumping facilities.
"Roll backs" would make life difficult. What does it mean to trace,
slowly step through execution, when the execution you are so painfully
following my be rolled back?. I would trade bushels of NULL messages
to avoid having to debug, validate and verify such a monster.
Performance is not the only consideration.
            

PS I am getting mail from the modsim mailing list but I am
an inexperienced mailer and my replies to "unni" and "modsim"
keep getting bounced back. Any advice would be helpful




Jerry Freedman, Jr      "As you wander through life
jfjr@mitre-bedford.arpa   Whatever be your goal
(617)271-6248 or 7555    Keep your eye upon the doughnut
                          and not on the hole"