I found this recent paper highly enlightening: “Real Differences between OT and CRDT for Co-Editors”– Chengzheng Sun, David Sun, Agustina, Weiwei Cai, October 2018.

Arxiv meta: https://arxiv.org/abs/1810.02137

PDF: https://arxiv.org/pdf/1810.02137.pdf

It’s well written imo. The conclusions chapter is very good.

“In this work, we have critically reviewed and evaluated representative OT and CRDT solutions, with respect to correctness, time and space complexity, simplicity, applicability in real world co- editors, and suitability in peer-to-peer co-editing. The evidences and evaluation results from this work disprove superiority claims made by CRDT over OT on all accounts.”

And it is also argued that OT is a more direct approach to the fundamental issues of realtime multiuser editing, and that that directness brings effectiveness.

HN discussion: https://news.ycombinator.com/item?id=18191867

This previous HN discussions on OT vs CRDT paper is an excellent overview of the topics [1],[2].

From the paper conclusions "Our discoveries from this work revealed facts and evidences that refute CRDT superiority claims over OT on all accounts, which helps to explain the underlying reasons behind the choices between OT and CRDT in the real world."

The fact that the paper provided the refutation to one of the HN discussion points being made in [1] (i.e. reference to itself), regarding the claimed of CRDT superiority in its footnotes is rather amusing and the first such attempt I have personally seen in a published paper.

[1]https://news.ycombinator.com/item?id=18191867

[2]https://arxiv.org/abs/1810.02137

I don't have much experience in this area, but I'd be interested in an overview of how different pieces of sofware handle the concurrent / multiplayer editing problem, like:

- Etherpad

- Google docs

- Apache / Google Wave (open sourced: http://incubator.apache.org/projects/wave.html)

- repl.it https://repl.it/site/blog/multi

- figma https://www.figma.com/blog/multiplayer-editing-in-figma/ (image editing rather than text editing)

So is the gist of it that OT relies on central servers and they all use OT rather than CRDT? That was not entirely clear to me.

Looking at the xi analysis, it sounds like "IME" is specific to a desktop application using X (?), so it doesn't apply to any of this web software.

The rest of them seem like they do apply?

Is the problem that you have to pay a "CRDT tax" for every piece of state in the application? I thought the same was true of OT. Don't you have to express every piece of state within those constraints too?

repl.it doesn't seem to have a problem with syntax highlighting or brace matching (try it, it's pretty slick). So is it just that they paid that tax with a lot of code or is there something else fundamentally different about xi vs. repl.it ? Or maybe xi is going for a lot lower latency than web-based editors?

recent thread about OT vs. CRDT that might be interesting: https://news.ycombinator.com/item?id=18191867

This reminds me of Oracle’s SCN which blew my mind back in ~2009 when I moved up from mysql home gamer stuff to the corporate world.

> Even long edit histories barely compare to the memory savings Zed obtains from not being built with Electron.

I got a good chuckle out of this. Speaking of performance, I think it’s I nteresting that ms word and google docs are still using OT rather than CRDT. The goog version seems to work well but I have had nothing but frustration with ms word. Bad merges and weird states are typical, particularly from the fat client.

Anyone else interested in the background of OT vs CRDT might find this thread useful: https://news.ycombinator.com/item?id=18191867