Differential Synchronization
Neil Fraser (via Mike Ash):
Keeping two or more copies of the same document synchronized with each other in real-time is a complex challenge. This paper describes the differential synchronization algorithm. Differential synchronization offers scalability, fault-tolerance, and responsive collaborative editing across an unreliable network.
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Differential synchronization is a symmetrical algorithm employing an unending cycle of background difference (diff) and patch operations. There is no requirement that "the chickens stop moving so we can count them" which plagues server-side three-way merges.
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Despite the inherent complexity, this synchronization system works extremely well. It is robust, self-healing and (with the proper diff and patch algorithms) impressively accommodating of users who are working on the same text.
