I'm hoping to hear some wisdom on the subject so I can decide if I'm
chasing a pipe dream or if it should be expected to work and I just need
to work out the kinks.
Finding things like this makes it sound possible:
but then again, in threads like this:
opinions are that it's just not reliable to trust.
My experience so far is that I eventually get repo corruption when I
stress it with concurrent read/write access from multiple hosts (beyond
any sort of likely levels, but still). Maybe I'm doing something wrong,
missing a configuration setting somewhere, put an unfair stress on the
system, there's a bona fide bug - or, given the inherent difficulty in
achieving perfect coherency between machines on what's visible on the
mount, it's just impossible (?) to truly get it working under all
My eventual usecase is to set up a bunch of (gitolite) hosts that all
are effectively identical and all seeing the same storage and clients
can then be directed to any of them to get served. For the purpose of
this query I assume it can be boiled down to be the same as n users
working on their own workstations and accessing a central repo on an NFS
share they all have mounted, using regular file paths. Correct?
I have a number of load-generating test scripts (that from humble
beginnings have grown to beasts), but basically, they fork a number of
code pieces that proceed to hammer the repo with concurrent reading and
writing. If necessary, the scripts can be started on different hosts,
too. It's all about the central repo so clients will retry in various
modes whenever they get an error, up to re-cloning and starting over.
All in all, they can yield quite a load.
On a local filesystem everything seems to be holding up fine which is
expected. In the scenario with concurrency on top of shared NFS storage
however, the scripts eventually fails with various problems (when the
timing finally finds a hole, I guess) - possible to clone but checkouts
fails, errors about refs pointing wrong and errors where the original
repo is actually corrupted and can't be cloned from. Depending on test
strategy, I've also had everything going fine (ops looks fine in my
logs), but afterwards the repo has lost a branch or two.
I've experimented with various NFS settings (e.g. turning off the
attribute cache), but haven't reached a conclusion. I do suspect that it
just is a fact of life with a remote filesystem to have coherency
problems with high concurrency like this but I'd be happily proven wrong
- I'm not an expert in either NFS or git.
So, any opionions either way would be valuable, e.g. 'it should work' or
'it can never work 100%' is fine, as well as any suggestions. Obviously,
the concurrency needed to make it probable to hit this seems so unlikely
that maybe I just shouldn't worry...
I'd be happy to share scripts and whatever if someone would like to try
it out themselves.
Thanks for your time,
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