Question

I am writing a Web application that has a user interface for editing data. The idea is something similar to a wiki where there are edits to chunks of text. What is the best way to handle asynchronous edits from multiple users? The situation I am considering is this:

There is a document that is version 0. User A is editing it when it is version 0. A few minutes later but before user A saves his changes, user B opens up the same document and starts editing. How should the server treat the two different edits to version 0 of the document? Also what is this problem called and where can I get more information about similar problems?

Answer 1

Wikipedia addresses this problem in the following way:

Assume that person A and person B are both editing the same document. Also assume person A submits their edits slightly before person B.

• First the media wiki software runs a traditional diffing algorithm over both edits.
• Next, the results of the diffing algorithm are used to merge the text.
• If the diffing algorithm finds that there are merge conflicts (i.e. person A and B edited the same piece of text), then person B is asked to resolve the conflicts since they submitted their edits last.

Wikipedia handles merge conflicts much like conflicts in a code repository.

If you want to allow multiple people to edit a document simultaneously and in real-time (like with google wave or etherpad), then I’d recommend looking into operational transforms (aka OT). Though the OT algorithm is no harder or simpler than a traditional diffing algorithm, there is less information on it and fewer ready-made implementations.