8 ms·
Collaborative Text Editing Without CRDTs or OT
- kelseyfrog 1y ago[flagged]
- esafak 1y agoHow reliable is that?
- sandeep1998 1y agomust be sarcasm I believe.
- deleted 1y ago[deleted]
- hencq 1y agoI'm not an expert on this, but the main difference with a CRDT like Automerge seems to be the server reconciliation. See for example this article [1]. Automerge handles concurrent insertions by using a sequence number and relying on an agreed ordering of agent ids when insertions are concurrent, while this scheme relies on the server to handle them in the order they come in. The article mentions this: > This contrasts with text-editing CRDTs, in which IDs are ordered for you by a fancy algorithm. That ordering algorithm is what differs between the numerous text-editing CRDTs, and it’s the complicated part of any CRDT paper; we get to avoid it entirely. I can buy the idea that many apps have a central server anyway, so you can avoid the "fancy algorithm", though the server reconciliation requires undoing and replaying of local edits, so it's not 100% clear to me if that's much simpler. [1] https://josephg.com/blog/crdts-go-brrr/ https://josephg.com/blog/crdts-go-brrr/
- hem777 1y agoAgreed, the undoing and replying isn’t exactly non-fancy. Peristent B+Tree is also not very non-fancy.
- mweidner 1y agoI believe that Automerge internally stores all operations in an eventually consistent total order, which you can use as a substitute for the server in server reconciliation (cf. https://mattweidner.com/2025/05/21/text-without-crdts.html#decentralized-variants https://mattweidner.com/2025/05/21/text-without-crdts.html#d...). However, Automerge does not actually do that - instead it processes text operations using a traditional CRDT, RGA, probably because (as you point out) undoing and replaying ops is not trivial to implement.
- hem777 1y agoCool to see a write up on this! Discovered the same method years ago and also wondered why it doesn’t show up in academic literature. I implemented this in a decentralized context and as a CRDT though, so that the properties hold (commutative, idempotent and associative).
- k__ 1y agoIf the idea is to have an alternative to CRDT, what did you gain from building it as CRDT?
- hem777 1y agoIt wasn’t really that we wanted to have a CRDT per se, but as it was implemented on top of an op-based append-only log CRDT, it turned out to hold those properties, which makes it a CRDT. We wanted to have the edits to be able to arrive in any order or after delays due to network partitions (this was for a p2p network).
- uh2010 1y agowonder if there would be a perf gain with UUIDv7
- poly2it 1y agoWhy not just use an ever incrementing u64?
- deleted 1y ago[deleted]
- zamadatix 1y agoAn incrementing u64 requires either atomic increments between concurrent clients or recalculation logic to consistently find the newly incremented ID after conflicting information syncs. UUIDs just spit out a unique ID without any complexity or associations with other clients.
- ChadNauseam 1y agoThere's closely related idea that might work, though. Each device editing text could be assigned a 32-bit ID by the server (perhaps auto-incrementing). Devices then maintain a separate 32-bit ID that they increment for each operation they perform. The ID used for each character is (device_id, edit_id), which should fit nicely in 8 bytes.
- mweidner 1y agoIndeed, this is close to what Yjs (popular CRDT library) does: each client instance (~ browser tab) chooses a random 32-bit clientId, and character IDs combine this clientId with local counters. https://github.com/yjs/yjs/blob/987c9ebb5ad0a2a89a0230f3a0c6b31f095d5f2d/src/utils/Doc.js#L64 https://github.com/yjs/yjs/blob/987c9ebb5ad0a2a89a0230f3a0c6... Any given collaborative document will probably only see ~1k clientIds in its lifetime, so the odds of a collision are fairly low, though I'd be more comfortable with a 64-bit ID.
- kortex 1y ago
- asdffdasy 1y agoso, an unoptimized crdt? just set max set size to 1 and yolo?
- th0ma5 1y agoIt's very appealing as a kind of irreducible complexity. It feels close to what is actually happening and is simple hahah if like you say not optimized.
- math_dandy 1y agoIs the take-home message of the post that the full complexity of CRDTs/OT is necessary only in the absence of a central server?
- sampton 1y agoOT requires centralized server.
- n_u 1y agoSome OTs do, some don't. OTs with the TP2 property do not require a central authority to order edits I believe. In my experience if you are persisting your edits or document state, you have something that creates an ordering anyways. That thing is commonly an OLTP database. OLTPs are optimized for this kind of write-heavy workload and there's a lot of existing work on how to optimize them further. But now even S3 has PUT-IF, so you could use that to create an ordering. https://docs.aws.amazon.com/AmazonS3/latest/userguide/conditional-requests.html https://docs.aws.amazon.com/AmazonS3/latest/userguide/condit...
- mweidner 1y agoEven in the absence of a central server, you can still avoid CRDT/OT complexity if you have a decentralized way to eventually total order operations & apply them in that order: https://mattweidner.com/2025/05/21/text-without-crdts.html#decentralized-variants https://mattweidner.com/2025/05/21/text-without-crdts.html#d... As others in the comments argue, this is technically a CRDT (though a fully general one); also, undoing/replaying ops is itself non-trivial to implement. However, I hope this is still simpler than using a traditional CRDT/OT for each data type.
- math_dandy 1y agoDid you perhaps mean to write, “though not a fully general one”?
- mweidner 1y ago
- apt-apt-apt-apt 1y agoDoes this finally solve collaborative text editing and its friends? Such an awesome approach.
- criddell 1y agoCould it? If you and I are simultaneously editing a list of people and you are trying to order them by age and I'm ordering them alphabetically, we are still going to have to reconcile the result.
- shermantanktop 1y agoBy that definition, it's not a solvable problem, is it?
- criddell 1y agoI don’t think so. AFAIK, CRDTs don’t solve semantic conflict issues.
- Footkerchief 1y agoSurprised to see no discussion of other data structures like dicts/maps, or arrays of arbitrary type. Hopefully they'd be a straightforward extension. IME, apps need collaborative data structures more often than they need pure collaborative text editing. The motivating examples (update validation, partial loading, higher-level operations) are interesting, but I don't see a strong case that the reason Yjs etc. lack these features is the underlying CRDT implementation, as opposed to these features being intrinsically difficult to build.
- filleokus 1y ago> Surprised to see no discussion of other data structures like dicts/maps, or arrays of arbitrary type. Hopefully they'd be a straightforward extension. IME, apps need collaborative data structures more often than they need pure collaborative text editing. Totally agree. I guess an array of "atomic" objects, where the properties of the objects can't be changed can be done just by replacing the string with your own type. Changes inside of the object is probably trickier, but maybe it's just about efficiently storing/traversing the tree? I've also always thoguth it should be possible to create something where the consumer of the helper library (per OP terminology) can hook in their own lightweight "semantic model" logic, to prevent/manage invalid states. A todo item can't both have isDone: true and state: inProgress at the same time. Similar to rich text formatting semantics mentioned in the linked article.
- SkiFire13 1y agoCRDTs essentially work by deterministically picking one side when a conflict arises. The issue is that in general this does not guarantee the lack of data loss nor data being valid (you can resolve the conflict between two pieces of valid data and get invalid data as a result). Imagine if every git merge conflict you got was resolved automatically by picking one side. Most of the time it would do the wrong thing, sometimes even leading to code that fails to compile. Imagine then you were not there ready to fix the issue, it would lead to even more chaotic results! This is why CRDTs are not more widespread, because they only fix the problem you think you have, not the problem you actually have, which is to fix conflicts in a way that preserves data, its validity and meaning. And arguably they make this issue even worse because they restrict the ways you can solve these conflicts to only those that can be replicated deterministically.
- deleted 1y ago[deleted]
- pshc 1y agoUse of server reconciliation makes me think client-side reconciliation would be tricky… how do you preserve smooth editor UX while applying server updates as they arrive? For example, if your client-sent request to insert a character fails, do you just retry the request? What if an update arrived in the intervening time? (Edit: they acknowledge this case in the “Client-Side” section, the proposal is to rewind and replay, and a simpler proposal to block until the pending queue is flushed) From a frontend vantage I feel like there may be a long tail of underspecified UI/UX edge cases, such that CRDT would be simpler overall. And how does the editor feel to use while riding the NYC subway where coverage is spotty?
- straws 1y agoBoth ProseMirror and the newer version of CodeMirror have a pretty elegant solution to this: each modification to the document is modeled as a step that keeps track of indices instead of node/text identities, and uses a data structure called a "position map" that the buffered steps can be mapped through to create steps with updated positions, which are then applied to your document. In practice, it works quite well. Here's more info: https://marijnhaverbeke.nl/blog/collaborative-editing.html https://marijnhaverbeke.nl/blog/collaborative-editing.html https://marijnhaverbeke.nl/blog/collaborative-editing-cm.html https://marijnhaverbeke.nl/blog/collaborative-editing-cm.htm...
- Animats 1y agoThat is very neat. The algorithm: - Label each text character with a globally unique ID (e.g., a UUID), so that we can refer to it in a consistent way across time - instead of using an array index that changes constantly. - Clients send the server “insert after” operations that reference an existing ID. The server looks up the target ID and inserts the new characters immediately after it. - Deletion hides a character for display purposes, but it is still kept for "insert after" position purposes. This might have potential outside text editing. Game world synchronization, maybe.
- yubblegum 1y agoIs this really that novel? I mean using a central process for serializing a distributed system is like a no brainer -- didn't we start off from here originally? -- until you have to worry about network partitions, and CAP and all that jazz. You also now have a single point of failure. Also I skimmed the thing but was performance discussed?
- bongodongobob 1y agoYeah I have the same question. I'm not familiar with the problem space but this seems like my naive first idea so I'm wondering what the catch is.
- mweidner 1y agoAs the author, same. My best guess is: - Central-server collaborative editing work focuses on Operational Transformation (OT), likely due to inertia (studied since 1989) and the perception that storing an ID per character is inefficient. In fairness, it is, absent the optimizations introduced by RGASplit and Yjs (~2015). - For decentralized editing, OT is very complicated, and CRDTs took over as the solution of interest (studied since 2005). Storing every operation permanently in a log - needed to use the linked approach without a server - feels inefficient, as does server reconciliation's undo/re-apply process. So CRDT research has focused on avoiding those inefficiencies, sacrificing simplicity along the way, instead of just embracing them as the easy way out. To me, the "inefficiencies" seem quite manageable. Storage is cheap, text is small, and you probably want a complete op log anyway for auditing and document histories (cf. git). Server reconciliation's undo/re-apply process can be batched aggressively, e.g., only do it a few times per second; that just makes remote ops take a little longer to show up. Granted, I have not built a complete app around server reconciliation or the linked approach, so perhaps there is a hidden catch. But I am encouraged by the success of Replicache (https://doc.replicache.dev/concepts/how-it-works https://doc.replicache.dev/concepts/how-it-works), which is where I learned of server reconciliation.
- deleted 1y ago[deleted]
- coolcase 1y agoIs collaborative text editing with offline sync a nerd snipe [0]? I work for a big tech and write a lot and usually worse case someone else edits at the same time and the server can figure it out. yes it needs some kind of algo but most concurrent edits are on different parts of a huge doc. Compare this to Git workflows. Git already handles merging most changes seamlessly. [0] https://xkcd.com/356/ https://xkcd.com/356/
- hbbio 1y agoSomeone should try to use a local LLM (maybe a 4b) to merge the diffs in case of conflict beyond straightforward cases... Not energy efficient but should work surprisingly well without CRDT, OT, or anything else.
- gregoriol 1y agoHow is an LLM supposed to merge the example from the article "My name is", insert "Charlie" after "is", insert "Dave" after "is"?
- practal 1y agoOk, so the main point that makes it different from CRDTs seems to be: if you have a central server, let the server do the synchronization (fixing an order among concurrent events), and not the data structure itself via an a-priori order. Because all communication is between client and server, and never between clients, when the client connects to the server, the server can make sure that it first processes all of the client's local operations before sending it new remote updates.
- lewisjoe 1y agoThis is technically a CRDT. It's just that the "order of operations" to apply over the doc is now resolved using a central server. For context, this is exactly how Google Docs and Zoho Writer works currently. Except that, they use OT with central-server based reconciliation and the proposal uses CRDT-istic approach. I agree this is more practical if your service anyway run over centralised servers (aka cloud)
- motorest 1y ago> This is technically a CRDT. It's just that the "order of operations" to apply over the doc is now resolved using a central server. This is not true. One of the most basic traits of CRDTs is that updates are performed without coordination. Relying on a central server to coordinate conflict resolution rejects two of the main traits of CRDTs. There is a name-drop, but there is no substance.