October 2008: It’s somewhat funny and somewhat sad to read this thread on the old USENET. Starting out with Andy Tanenbaum’s proposed list of accepted truths (most of which I thought wrong at the time)
GENERALLY ACCEPTED AS TRUE BY RESEARCHERS IN DISTRIBUTED SYSTEMS
- – The client-server paradigm is a good one
- – Microkernels are the way to go
- – UNIX can be successfully run as an application program
- – RPC is a good idea to base your system on
- – Atomic group communication (broadcast) is highly useful
- – Caching at the file server is definitely worth doing
- – File server replication is an idea whose time has come
- – Message passing is too primitive for application programmers to use
- – Synchronous (blocking) communication is easier to use than asynchronous
- – New languages are needed for writing distributed/parallel applications
- – Distributed shared memory in one form or another is a convenient model
and then Rob Pike’s refutation entitled “Andy Tanenbaum hasn’t learned anything”. A key point that comes up later in the discussion is Tanenbaum’s (incorrect) assertion that a “factor of two” performance loss is nothing to worry about. The date of the discussion is interesting, because in a few years the Linux Tsunami washed away most of the landscape of this discussion. As for my contribution it is very disturbing to see that I have not learned much about those topics in the last 14
16 23 years. (updated again in 2015)
It is clear that Rob Pike was right on many more issues than AST, but that seemed clear at the time too.
Subject: Andy Tanenbaum hasn’t learned anything
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
– 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)
– 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.
Distributed shared memory – an idea that never made any sense to me.
[edited to reflect the passage of time][ and again to add the Pike/Presott/Thompson/Winterbottom text]