Hi

Basically, I'm at a place where I'm considering giving up getting this to work reliably. In general, my setup work really fine, except for the itty-bitty detail that when I put pressure on things I tend to get into various kinds of trouble with the central repo being corrupted.


Can anyone authoritatively state anything either way?

TIA,

ken1

On 2013-03-28 11:22, Kenneth Ölwing wrote:
Hi,

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:
  http://permalink.gmane.org/gmane.comp.version-control.git/122670
but then again, in threads like this:
  http://kerneltrap.org/mailarchive/git/2010/11/14/44799
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 situations.

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,

ken1

--
To unsubscribe from this list: send the line "unsubscribe git" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html


--
To unsubscribe from this list: send the line "unsubscribe git" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Reply via email to