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From: douglis@ALLSPICE.BERKELEY.EDU (Fred Douglis)
Newsgroups: comp.os.misc
Subject: Re: Test for distributedness
Keywords: distributed system sprite process migration
Message-ID: <9003260052.AA262747@sprite.Berkeley.EDU>
Date: 26 Mar 90 00:52:08 GMT
References: <6117@star.cs.vu.nl> <6067@star.cs.vu.nl> <2604@quiche.cs.mcgill.ca> <6106@star.cs.vu.nl> <6548@becker.UUCP>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: U.C. Berkeley Sprite Project
Lines: 38

Sprite would not pass Andy's test for distributedness, though it, too,
would come close.  Originally we had the notion that workstations
wouldn't even have hostnames -- a workstation would just be a display
onto a distributed time-sharing system.  The problem is that making
everything anonymous, including machines on people's desks, would make
it harder to distinguish between machines. The rest of the world
believes in separate hosts.  For example, what if someone from sprite
wanted to rlogin to a unix machine?  If rlogin just claimed to be from
a single internet address "sprite.Berkeley.EDU", then all packets
would have to be routed via that machine, even though my own
workstation is capable of running IP/TCP and communicating directly.
But "finger" on sprite lists all users on all sprite workstations,
including which workstation each user is most recently active on, and
mail goes out as "sprite".  There's a single shared file system.  The
real distinction between Sprite and Andy's distributed system is that
we name our workstations and can rlogin between them.

With respect to load sharing, we provide transparent remote execution
(users on one host can run "pmake" and other programs to use multiple
hosts in parallel) but we also provide performance guarantees to the
owner of a workstation.  Andy suggests that in a true distributed
system, all processors are available to all users, and someone on one
machine would notice a performance degradation when someone else on
another machine started a large program.  This is true, and to us it
suggests that we don't necessarily want a "true" distributed system,
only something close.  In Sprite, anyone can use idle hosts, but if a
user comes back to a host that's running someone else's processes, the
foreign processes get migrated back to the originator's machine.
People who are now using Sprite seem to uniformly appreciate the
ability to control their own machine.

I'd be interested in hearing how other people address this issue.  Do
you think workstation ownership is a reasonable notion, or is it
outdated?

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Fred Douglis		douglis@sprite.Berkeley.EDU	ucbvax!douglis
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