[Gluster-devel] file version on glusterfs using libgit

[Niels de Vos]

On Fri, Mar 08, 2013 at 06:00:24AM -0500, Shishir Gowda wrote:
> Hi Niels,
> 
> Thinking out aloud, I think the snaps(in file version context) can be 
> displayed as branches (list).

Well, I am not sure if branches are really needed. Isn't linear history 
sufficient? Every change should be committed to the master branch 
anyway. Branches may be useful for switching between versions, but 
nothing prevents you from checking out (or "git ls-files") with a comit 
or a date.

I'm thinking of a virtual .snaps directory:

$ cd $VOLUME/.snaps
$ ls
2013-03-07/
2013-03-06/
.....
current/
changelog
yesterday -> 2013-03-07/

This makes it possible to do something like:
$ cat changelog
   - virtual file, showing the contents of 'git log'
   - find a commit you're interested in
$ mkdir $GIT_COMMIT_ID
$ ls $GIT_COMMIT_ID/
   - get the state just like 'git checkout $GIT_COMMIT_ID'

Maybe it would be helpful to be able to create tags inside this .snaps 
directory. But I would refrain from branches for now (unless there is 
a clear use-case).

Cheers,
Niels

> Once the user cd's into any one of them, we could do a git checkout of the branch.
> 
> That should mimic the behaviour.
> 
> With regards,
> Shishir
> 
> ----- Original Message -----
> From: "Shishir Gowda" <sgowda at redhat.com>
> To: "Niels de Vos" <ndevos at redhat.com>
> Cc: gluster-devel at nongnu.org
> Sent: Friday, March 8, 2013 4:04:42 PM
> Subject: Re: [Gluster-devel] file version on glusterfs using libgit
> 
> Hi Niels,
> 
> My inclination too is to load git ontop of posix xlator.
> 
> I was thinking of making previous versions (based on some policy) to be treated a new branch.
> 
> We could see how to export these branches as user visible dirs.
> 
> With regards,
> Shishir
> 
> ----- Original Message -----
> From: "Niels de Vos" <ndevos at redhat.com>
> To: "Shishir Gowda" <sgowda at redhat.com>
> Cc: gluster-devel at nongnu.org
> Sent: Friday, March 8, 2013 3:25:57 PM
> Subject: Re: [Gluster-devel] file version on glusterfs using libgit
> 
> On Thu, Mar 07, 2013 at 12:54:41AM -0500, Shishir Gowda wrote:
> > Hi All,
> > 
> > Was playing around with git on glusterfs volume, to provide was of file version support.
> > 
> > And initial run is encouraging.
> > 
> > A brief overview what was tried:
> > 
> > Approach 1: Glusterfs volume as a git repo
> > 
> > 1. created a 2 brick distribute volume
> > 2. inited a git repo on fuse volume
> > 3. created files, committed them in git.
> > 4. Modified files, and committed them again
> > 5. Did branch check-outs, to simulate versions @ point in time
> > 6. reset branch heads, and was able access older version of files (after a stash).
> > 7. Was able to create files/dirs/symlinks/hardlinks
> > 8. Both NFS/FUSE clients were used.
> > 
> > Approach 2: Glusterfs bricks as git repo's
> > 
> > 1. created a 2 brick distribute volume
> > 2. inited git repo on brick1
> > 3. inited git repo on brick2
> > 4. created files, committed the relevant brick's git.
> > 5. Modified files, and committed them again on brick's git
> > 6. Did branch check-outs, to simulate versions @ point in time on individual bricks
> > 7. reset branch heads, and was able access older version of files (after a stash).
> > 8. Was able to create files/dirs/symlinks/hardlinks
> > 9. Both NFS/FUSE clients were used.
> > 
> > Buoyed by this, will start prototyping integration of libgit2 as xlator for file version support.
> > 
> > There are 3 approaches to consider:
> > 
> > 1. Load git xlator on clients volfiles
> > 2. Load git xlator on server volfiles
> > 3. Replace posix interface with git interface.
> > 
> > Please provide feedback, on what would be more desirable.
> 
> Very interesting! Option 2 makes most sense to me, the posix xlator 
> contains some access checks and such, which you probably should not need 
> to duplicate.
> 
> Have you thought about making the previous version accessible through 
> the glusterfs/nfs mount? Other vendors seem to have a .snapshot 
> directory with previous versions, would something like that be possible?  
> Users would be able to recover deleted files themselves that way.
> 
> Also, I do not know if git stores xattrs and their changes...
> 
> Cheers,
> Niels
> 
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-- 
Niels de Vos
Sr. Software Maintenance Engineer
Support Engineering Group
Red Hat Global Support Services