Concurrency in a GIT repo on a network shared folder

Question

Hello,

I want to have a bare git repository stored on a (windows) network share. I use linux, and have the said network share mounted with CIFS. My coleague uses windows xp, and has the network share automounted (from ActiveDirectory, somehow) as a network drive.

I wonder if I can use the repo from both computers, without concurrency problems.

I've already tested, and on my end I can clone ok, but I'm afraid of what might happen if we both access the same repo (push/pull), at the same time.

In the git FAQ there is a reference about using network file systems (and some problems with SMBFS), but I am not sure if there is any file locking done by the network/server/windows/linux - i'm quite sure there isn't.

So, has anyone used a git repo on a network share, without a server, and without problems?

Thank you,
Alex

PS: I want to avoid using an http server (or the git-daemon), because I do not have access to the server with the shares. Also, I know we can just push/pull from one to another, but we are required to have the code/repo on the share for back-up reasons.

Update:

My worries are not about the possibility of a network failure. Even so, we would have the required branches locally, and we'll be able to compile our sources.

But, we usually commit quite often, and need to rebase/merge often. From my point of view, the best option would be to have a central repo on the share (so the backups are assured), and we would both clone from that one, and use it to rebase.

But, due to the fact we are doing this often, I am afraid about file/repo corruption, if it happens that we both push/pull at the same time. Normally, we could yell at each other each time we access the remote repo :), but it would be better to have it secured by the computers/network.

And, it is possible that GIT has an internal mechanism to do this (since someone can push to one of your repos, while you work on it), but I haven't found anything conclusive yet.

Update 2:

The repo on the share drive would be a bare repo, not containing a working copy.

Answer 1

Why bother? Git is designed to be distributed. Just have a repository on each machine and use the publish and pull mechanism to propagate your changes between them.

For backup purposes, run a nightly task to copy your repository to the share.

Or, create one repository each on the share and do your work from them but use them as distributed repositories from which you can pull changesets from each other. If you use this method, then performance of doing builds and so on will be decreased since you will be constantly accessing over the network.

Or, have distributed repositories on your own computers, and run a periodic task to push your commits to the repositories on the share.

Answer 2

Sounds just as if you'd rather like to use a centralized versioning system, so the query for backup is satisifed. Perhaps with xxx2git in between for you to work locally.

Answer 3

Git requires minimal file locking, which I believe is the main cause of problems when using this kind of shared resource over a network file system. The reason it can get away with this is that most of the files in a Git repo--- all the ones that form the object database--- are named as a digest of their content, and immutable once created. So there the problem of two clients trying to use the same file for different content doesn't come up.

The other part of the object database is trickier-- the refs are stored in files under the "refs" directory (or in "packed-refs") and these do change: although the refs/* files are small and always rewritten rather than being edited. In this case, Git writes the new ref to a temporary ".lock" file and then renames it over the target file. If the filesystem respects O_EXCL semantics, that's safe. Even if not, the worst that could happen would be a race overwriting a ref file. Although this would be annoying to encounter, it should not cause corruption as such: it just might be the case that you push to the shared repo, and that push looks like it succeeded whereas in fact someone else's did. But this could be sorted out simply by pulling (merging in the other guy's commits) and pushing again.

In summary, I don't think that repo corruption is too much of a problem here--- it's true that things can go a bit wrong due to locking problems, but the design of the Git repo will minimise the damage.

(Disclaimer: this all sounds good in theory, but I've not done any concurrent hammering of a repo to test it out, and only share them over NFS not CIFS)

Answer 4

Apparently using a central git repo is supported. Most prescribed uses indicate ssh or http access, neither of which avoid the simultaneous access to the repo. Even if you are doing completely distributed usage, this question arises if more than two collaborators push to the same repo anywhere. So far, no response has answered the question. Does the design of git allows it to handle N simultaneous pushes to a branch?