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by mweidner 100 days ago
The PowerSync folks and I worked on a different approach to ProseMirror collaboration here: https://www.powersync.com/blog/collaborative-text-editing-ov... It is neither CRDT nor OT, but does use per-character IDs (like CRDTs) and an authoritative server order of changes (like OT).

The current implementation does suffer from the same issue noted for the Yjs-ProseMirror binding: collaborative changes cause the entire document to be replaced, which messes with some ProseMirror plugins. Specifically, when the client receives a remote change, it rolls back to the previous server state (without any pending local updates), applies the incoming change, and then re-applies its pending local updates; instead of sending a minimal representation of this overall change to ProseMirror, we merely calculate the final state and replace with that.

This is not an inherent limitation of the collaboration algorithm, just an implementation shortcut (as with the Yjs binding). It could be solved by diffing ProseMirror states to find the minimal representation of the overall change, or perhaps by using ProseMirror's built-in undo/redo features to "map" the remote change through the rollback & re-apply steps.
1 comments
antics 100 days ago
Hi Matt! Good to see you here. For those who don't know, Matt also wrote a blog about how to do ProseMirror sync without CRDTs or OT here: https://mattweidner.com/2025/05/21/text-without-crdts.html and I will say I mostly cosign everything here. Our solution is not 100% overlap with theirs, but if it had existed when we started we might not have gone down this road at all.
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mweidner 100 days ago
Your part 1 post was one of the inspirations for that :)

Specifically, it inspired the question: how can one let programmers customize the way edits are processed, to avoid e.g. the "colour" -> "u" anomaly*, without violating CRDT/OTs' strict algebraic requirements? To which the answer is: find a way to get rid of those requirements.

*This is not just common behavior, but also features in a formal specification [1] of how collaborative text-editing algorithms should behave! "[The current text] contains exactly the [characters] that have been inserted, but not deleted."

[1] http://www.cs.ox.ac.uk/people/hongseok.yang/paper/podc16-ful...

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