Real Differences Between OT and CRDT in Building Co-Editing Systems

Real Differences Between OT and CRDT in Building Co-Editing Systems

[Submitted on 2 May 2019 (v1), last revised 10 Jun 2020 (this version, v2)]

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Abstract: OT (Operational Transformation) was invented for supporting real-time
co-editors in the late 1980s and has evolved to become a core technique used in
today’s working co-editors and adopted in major industrial products. CRDT
(Commutative Replicated Data Type) for co-editors was first proposed around
2006, under the name of WOOT (WithOut Operational Transformation). Follow-up
CRDT variations are commonly labeled as “post-OT” techniques and have made
broad claims of superiority over OT solutions, in terms of correctness, time
and space complexity, simplicity, etc. Over one decade later, however, OT
remains the choice for building the vast majority of co-editors, whereas CRDT
is rarely found in working co-editors. Why? To seek truth from facts, we set
out to conduct a comprehensive and critical review of representative OT and
CRDT solutions and working co-editors based on them. From this work, we have
made important discoveries about OT and CRDT, and revealed facts and evidences
that refute CRDT claims over OT on all accounts. We present our discoveries in
three related and complementary articles.

In prior two articles, we have revealed the similarities of OT and CRDT in
following the same general transformation approach in co-editors, and their
real differences in correctness and complexity. In this article, we examine the
role of building working co-editors in shaping OT and CRDT research and
solutions, and consequential differences in the choice between OT and CRDT in
real world co-editors and industry products. In particular, we review the
evolution of co-editors from research vehicles to real world applications, and
discuss representative OT-based co-editors and alternative approaches in
industry products and open source projects. Moreover, we evaluate CRDT-based
co-editors in relation to published CRDT solutions, and clarify some myths
surrounding “peer-to-peer” co-editing.

Submission history From: Chengzheng Sun [view email]

Thu, 2 May 2019 10:10:28 UTC (1,153 KB)
Wed, 10 Jun 2020 15:15:23 UTC (1,168 KB)

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