Source Control HOWTO: Repositories

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  • inside a firewall. If you need to allow your developers to access the repository from home, carefully poke a hole, but leave everything else as tight as you can. Make sure your developers are using some sort of bulk encryption. Vault uses SSL. Tools like Perforce, CVS and Subversion can be tunneled through ssh or something similar.

This brief list of tips is hardly a complete guide for administrators. I am merely trying to describe the level of care and caution which should be used for your SCM repository.

Undo
As I have mentioned, one of the best things about source control is that it contains your entire history. Every version of everything is stored. Nothing is ever deleted.

However, sometimes this benefit can be a real pain. What if I made a mistake and checked in something that should not be checked in? My history contains something I would rather forget. I want to pretend that it never happened. Isn't there some way to really delete from a repository?

In general, the recommended way to fix a problem is to checkin a new version which fixes it. Try not to worry about the fact that your repository contains a full history of the error. Your mistakes are a part of your past. Accept them and move on with your life.

However, most SCM tools do provide one or more ways of dealing with this situation. First, there is a command I call "rollback". This command is essentially an "undo" for revisions of a file. For example, let's say that a certain file is at version 7 and we want to go back to version 6. In Vault, we select version 6 and choose the Rollback command.

To be fair, I should admit that the rollback command is not always destructive. In some SCM tools, the rollback feature really does make version 7 disappear forever. Vault's rollback is non-destructive. It simply creates a version 8 which is identical to version 6. The designers of Vault are fanatical purists, or at the very least, one of them is.

As a concession to those who are less fanatical, Vault does support a way to truly destroy things in a repository. We call this feature "obliterate". I believe Subversion and Perforce use the same term. The obliterate command is the only way to delete something and make it truly gone forever.

Best Practice: Never Obliterate Anything That was Real Work
The purist in me wants to recommend that nothing should ever be obliterated. However, my pragmatist side prevails. There are situations where obliterate is not sinful.

However, obliterate should never be used to delete actual work. Don't obliterate a file simply because you discovered it to be a bad idea. Don't obliterate a file simply because you don't need it anymore. Obliterate is for situations where something in the repository should never have been there at all. For example, if you accidentally checkin a gigabyte of MP3s alongside your C++ include files, obliterate is a justifiable choice.

In my original spec for Vault, I had decided that we would not implement any form of destructive delete. We eventually decided to compromise and implement this command, but I really wanted to discourage its use. SourceSafe makes it far too easy to rewrite history and pretend that something never happened. In the Delete dialog box, SourceSafe includes a checkbox called "Destroy Permanently". This is an atrocious design decision, roughly equivalent to leaving a sledgehammer next to the server machine so that people can bash the hard disks with it every once in a while. This

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