deltified document revision control in PHP

If I have a PHP application which allows users to make changes to documents, what is the best way to implement revision tracking for each document? I want the storage of开发者_Go百科 each revision to be deltified (i.e. only save the changes that were made) like svn and other SCMs do with code. I know on a very simple level how it works, but when I start to think about implementing it, I get a little confused.

First and foremost, I am wondering if there is a library out there that can help me with this, so I don't have to completely roll my own.

And I am wondering: should I keep the full text of only the original document, and then only save the changes, or should I keep the full text of the latest document, and each time it is modified, save the differences as one of the older revisions?

If the former, then when I want to grab a page to be shown on the site, do I have to start at the beginning, and then recursively update the data based on the revisions, until I reach the current version? Won't this be painfully slow once there are many revisions?

How can I do diff/patch type operations in PHP to make the deltifying and reconstructing of the pages easier?

Would it be worth it to have locks on the pages when they're editing them? Or let pages get into 'states of conflict' and have conflict resolution operations -- let two users modify the same page simultaneously if they're modifying different parts, etc -- I'm going crazy thinking about how hard this will be. Ahh!

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This previous SO question might help.

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Why don't you use a subversion server? You can access the client from the console using exec() or similar. It is really not worth implementing something like that from scratch unless this you are writing a revisioning software.