Andy Tanenbaum hasn't learned anything

[rob@alice.att.com (research!rob)]

The implementers of Plan 9 are baffled by Andy Tanenbaum's recent posting.
We suspect we are not representative of the mainline view, but we disagree
at some level with most of the "GENERALLY ACCEPTED" truths Andy claims.
Point by point:

   - The client-server paradigm is a good one
	Too vague to be a statement.  "Good" is undefined.
   - Microkernels are the way to go
	False unless your only goal is to get papers published.
	Plan 9's kernel is a fraction of the size of any microkernel
	we know and offers more functionality and comparable
	or often better performance.
   - UNIX can be successfully run as an application program
	`Run' perhaps, `successfully' no.  Name a product that succeeds
	by running UNIX as an application.
   - RPC is a good idea to base your system on
	Depends on what you mean by RPC.  If you predefine the complete
	set of RPC's, then yes.  If you make RPC a paradigm and expect
	every application to build its own (c.f. stub compilers), you
	lose all the discipline you need to make the system comprehensive.
   - Atomic group communication (broadcast) is highly useful
	Perhaps.  We've never used it or felt the need for it.
   - Caching at the file server is definitely worth doing
	True, but caching anywhere is worthwhile.  This statement is
	like saying 'good algorithms are worth using.'
   - File server replication is an idea whose time has come
	Perhaps.  Simple hardware solutions like disk mirroring solve a
	lot of the reliability problems much more easily.  Also, at least
	in a stable world, keeping your file server up is a better way to
	solve the problem.	
   - Message passing is too primitive for application programmers to use
	False.
   - Synchronous (blocking) communication is easier to use than asynchronous
	They solve different problems.  It's pointless to make the distinction
	based on ease of use.  Make the distinction based on which you need.
   - New languages are needed for writing distributed/parallel applications
	`Needed', no.  `Helpful', perhaps.  The jury's still out.
   - Distributed shared memory in one form or another is a convenient model
	Convenient for whom?  This one baffles us: distributed shared memory
	is a lousy model for building systems, yet everyone seems to be
	doing it.  (Try to find a PhD this year on a different topic.)

How about the "CONTROVERSIAL" points?  We should weigh in there, too:

   - Client caching is a good idea in a system where there are many more
     nodes than users, and users do not have a "home" machine (e.g., hypercubes)
	What?
   - Atomic transactions are worth the overhead
	Worth the overhead to whom?
   - Causal ordering for group communication is good enough
	We don't use group communication, so we don't know.
   - Threads should be managed by the kernel, not in user space
	Better: have a decent process model and avoid this process/thread
	dichotomy.


Rob Pike
Dave Presotto
Ken Thompson
Phil Winterbottom