Mercurial local repository backup

Question

I'm a big fan of backing things up. I keep my important school essays and such in a folder of my Dropbox. I make sure that all of my photos are duplicated to an external drive. I have a home server where I keep important files mirrored across two drives inside the server (like a software RAID 1).

So for my code, I have always used Subversion to back it up. I keep the trunk folder with a stable copy of my application, but then I create a branch named with my username, and inside there is my working copy. I make very few changes between commits to that branch, with the understanding that the code in there is my backup.

Now I'm looking into Mercurial, and I must admit I haven't truly used it yet so I may have this all wrong. But it seems to me that you have a server-side repository, and then you clone it to a working directory in the form of a local repository. Then as you work on something, you make commits to that local repository, and when things are in a state to be shared with others, you hg push to the parent repository on the server.

Between pushes of stable, tested, bug-free code, where is the backup?

After doing some thinking, I've come to the conclusion that it is not meant for backup purposes and it assumes you've handled that on your own. I guess I need to keep my Mercurial local repositories in my dropbox or some other backed-up location, since my in-progress code is not pushed to the server.

Is this pretty much it, or have I missed something? If you use Mercurial, how do you backup your local repositories? If you had turned on your computer this morning and your hard drive went up in flames (or, more likely, the read head went bad, or the OS corrupted itself, ...), what would be lost? If you spent the past week developing a module, writing test cases for it, documenting and commenting it, and then a virus wipes your local repository away, isn't that the only copy?

So then on the flip side, do you create a remote repository for every local repository and push to it all the time?

How do you find a balance? How do you ensure your code is backed up? Where is the line between using Mercurial as backup, and using a local filesystem backup utility to keep your local repositories safe?

Answer 1

It's ok thinking of Subversion as a 'backup', but it's only really doing that by virtue of being on a separate machine, which isn't really intrinsic to Subversion. If your Subversion server was the same machine as your development machine - not uncommon in the Linux world - you're not really backed up in the sense of having protection from hardware failure, theft, fire, etc. And in fact, there is some data in that case that is not backed up at all - your current code may exist in two places but everything else in the repository (eg. the revision history) only exists in one place, on the remote server.

It's exactly the same for Mercurial except that you've taken away the need for a separate server and thus made it so that you have to explicitly think about backing up rather than it being a side-effect of needing to have a server somewhere. You can definitely set up another Mercurial repository somewhere and push your changes to that periodically and consider that your backup. Alternatively, simply backup your local repository in the same way that you'd back up any other important directory. With you having a full copy of the repository locally, including all revision history and other meta data, this is arguably even more convenient and safe than the way you currently do it with Subversion.

Answer 2

The "hidden" .hg directory stores all of the local commits. You can back up this directory using a standard backup program.

Answer 3

The changes get to the remote directory only when you push. Commits stay local, but you get them if you clone your repository. Then, yes, if you want your things to get to the server repository you have to push to it "all the time".

On the other hand, nothing stops you to have several machines and push content from one to another. Every mercurial repository can turn itself into a server in a matter of seconds typing "hg serve".

I'm not sure it really answer to you question, but I too am a big fan of backup and manage things this way with many clones of my repository (I also use massively mq to work in patch mode but that's another story).

PS: as a sidenote, I'm considering to use mercurial as a tool for filesystem backup. The only thing that bother me is that for this purpose I would prefer to disable the diff feature and treat all files as binary, but that should be easy.