[Gluster-users] glusterfs performance issues

[Whit Blauvelt]

On Tue, Jan 08, 2013 at 02:42:49PM +0100, Stephan von Krawczynski wrote:

> What an dead-end argument. _Nothing_ will save you in case of a split-brain.

So then, to your mind, there's _nothing_ Gluster can do to heal after a
split brain? Some non-trivial portion of the error scenarios discussed in
this thread result from a momentary or longer split-brain situation. I'm
using "split-brain" in the broad sense of any situation where two sides of a
replicated system are out-of-touch for some period and thus get out-of-sync.
Isn't that exactly what we're discussing, how to heal from that? Sure, you
can have instances of specific files beyond algorithmic treatment. But
aren't we discussing how to ensure that the largest possible portion of the
set of files amenable to algorithmic treatment are so-handled?

> > That's the thing about complex systems. Trivial solutions are usually both
> > simple and wrong. Some work most of the time, but there are corner cases. As
> > we see with Gluster even complex solutions tend to have corner cases; but at
> > least in complex solutions the corners can be whittled down.
> 
> Can they? I'd rather say if it is non-trivial it is broken most of the time.
> Ask btrfs for confirmation.

Pointing out that a complex system can go wrong doesn't invalidate complex
systems as a class. It's well established in ecological science that more
complex natural systems are far more resiliant than simple ones. A rich,
complex local ecosystem has a higher rate of stability and survival than a
simple, poorer one. That's assuming the systems are evolved and have niches
well-fitted with organisms - that the complexity is organic, not just
random.

Computer software, hardware, and the human culture that supports them also
form complex, evolved ecosystems. Can there be simple solutions that help
optimize such complex systems? Sure. But to look only for simple solutions
is to be like the proverbial drunk looking for his keys under the
streetlight, even though he heard them drop a half-block away, because "The
light is better here." When people try to apply simple solutions to complex,
evolved ecosystems, the "law of unintended consequences" is more the rule
than the exception. Solutions that appear simple and obvious should always
be suspect. Granted, complex, obscure ones also require scrutiny. It's just,
the simple stuff should never get a pass.

Best,
Whit