[Gluster-users] glusterfs performance issues - meta

[Stephan von Krawczynski]

On Tue, 8 Jan 2013 11:44:15 -0500
Whit Blauvelt <whit.gluster at transpect.com> wrote:

> On Tue, Jan 08, 2013 at 04:49:30PM +0100, Stephan von Krawczynski wrote:
> 
> > > 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 resilient 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.
> > 
> > That is a good example for excluded corner cases, just like the current split
> > brain discussion. All I need to do to your complex natural system to
> > invalidate is to throw a big stone on it. Ask dinosaurs for real life
> > experience after that. 
> 
> Throw a big enough stone and anything can be totally crushed. The question
> is one of resilience when the stone is less than totally crushing. The
> ecosystem the big stone was thrown at which included the dinosaurs survived,
> because in its complexity it also included little mammals - which themselves
> were more complex organisms than the dinosaurs. Not that some simpler
> organisms didn't make it through the extinction event too. Plenty did. The
> chicken I ate for dinner is a descendant of feathered dinosaurs.
> 
> Take two local ecosystems, one more complex than the other. Throw in some
> big disturbance, the same size of disruption in each. On average, the
> complex local ecosystem is more likely to survive and bounce back, while the
> simple one is more likely to go into terminal decline. This is field data,
> not mere conjecture. Your argument here could be that technological systems
> don't obey the same laws as ecosystems. But work in complexity theory shows
> that the right sorts of complexity produce greater stability across a broad
> range of systems, not just biological ones. 
> 
> Free, open source software's particular advantage is that it advances in a
> more evolutionary manner than closed software, since there is evolutionary
> pressure from many directions on each part of it, at every scale.
> Evolutionary pressure produces complexity, the _right sort_ of complexity.
> That's why Linux systems are more complex, and at the same time more stable
> and manageable, than Windows systems. 
> 
> Simplicity does not have the advantage. Even when smashing things with
> rocks, the more complex thing is more likely to survive the assault, if it
> has the right sort of complexity.

Listen, I don't really want to lengthen the discussion about complexity issues
in ecosystems. But let me please point out that the fundamental flaw in your
example as you turn it now is that a natural ecosystem has no _goal_ of
existence. Whereas programmed code should at least have _some_.
Which means you can take it as negative example for reasons why something does
not work. But you cannot elaborate it as positive example why something should
work. Glusterfs(d) has a clearly stated goal of being, an ecosystem has not.
So you cannot say that only because _something_ survived a crashing ecosystem
proves that an equally complex code does something useful after an equally
complex crash. In fact it most certainly does not.
Contrary is true. You should strip down complexity to the lowest possible
level to make the code more obvious and therefore more debuggable and readable
to a larger number of people. That will have a positive effect on its
stability. But if you throw in more and more code for fragile corner cases
instead of drawing a clear line between "clearly working" and "clearly
failing" you will not end up at the desired state where everything works
stable.
This path is as wrong as it was to release a complete fileserver installation
image back in the old days of glusterfs.
In the end, everything boils down to the question where efforts are invested
best in order to make the project more successful. And its really not that
hard to find out what the biggest show stopper is. simply count the articles
in the list dealing with performance issues and strange effects of not-synced
files during _normal_ operation. there is not much left.
Read the fs comparison between NFS, Samba, Ceph and Glusterfs in some german
linux magazine lately? Guess who's last...

> Best,
> Whit

-- 
Regards,
Stephan