Realtime collaboration

Hi,

we’re building a collaborative learning platform in Meteor/React (FROG), where we’re using ShareDB heavily - both ot-json as the backing store for collaborative activities (activities are pluggable, and they get access to a shared document, which they can structure as they want - this gives us a lot of flexibility), and ot-text for collaborative text editing. We are having some problems scaling up (both because of Meteor and possibly ShareDB), and I dream of having a “OT as a service” thing, where I could just run an Elixir server or cluster, which would be compatible with the front-end ShareDB client (or something similar). All the JS code could be kept - and it would be super-fast, scaleable etc.

I did try a few years ago to rewrite the login in ot-text to Elixir, it was an interesting exercise… It’s pretty functional code (all functions which take an input and produce an output without side-effects), but they use closures a lot, which I changed to recursive functions. I even set up a way to run the (very extensive) JS test harness for ot-text against my library - and it got pretty far. I never fixed all the failing tests, and I kind of abandoned it, because I didn’t have the push to move it forwards (I was in the middle of running experiments for my PhD thesis, and didn’t actually need it. My very old abandoned attempt.

I still think OT is amazingly powerful, and it seems tailor-made for Elixir… I would love to see someone try again to make a production-ready OT server in Elixir - having a compatibility mode with ShareDB would let a lot of products switch easily, and would work well with existing extensions like Rich text etc, but investigating a more efficient transmission format would be interesting too…

Note that the ShareDB people have been working on a new version of ot-json for years, which apparently is soon ready.

If you pursue this, please let me know, as I’d be very interested to follow along, and maybe use it. We’re also working on collaborative writing analytics (predict collaboration quality etc), if anyone is interested.

best
Stian Håklev
Ecole Polytechnique Fédérale de Lausanne

More about how we use ShareDB here https://groups.google.com/d/msg/sharejs/N7QBY-qI2O4/EhFPxF2GAgAJ

I don’t think it’s possible to do better than what they already have. They are talking about adding conflict markers, which destroys the ergonomics completely.

I haven’t read your account of using ShareDB in production yet. I need to dedicate a solid block of time to that because it’s packed with useful information.

It seems like you’re having lots of problems with the transformation functions. I wasn’t expecting them to be a bottleneck. Did you investigate CRDTs (especially delta-CRDTs)? You’d have (probably much) higher memory requirements, but “transformations” would be quicker. You’d have problems rendering the underlying CRDT into JSON, but that work can be offloaded to the clients (the server might not even need to render anything).

tmbb: Sorry, what is the context of your comment? Are you talking about our
issues with scaling ShareDB, or with my initial attempt at translating
ot-text into Elixir? If it’s the first one, I think a bigger concern is the
number of websockets that can be connected to a ShareDB instance at a time,
not so much what they are doing (we haven’t really found this to be a
bottleneck at least). The one problem we had was efficiently creating
hundreds of different documents at a time, but this is a single create
operation, it’s more because of the asynchronous nature of creating a
document from a ShareDB client. If ShareDB had a command (or we built an
extension into the client), which could take as an argument a dict of
objectid: content, and batch-create all the new documents, it would be
super-fast (and already it’s decent for us).

I have been reading a bit about CRDTs etc - they seem more appropriate for
peer2peer stuff, and not so necessary where you will anyway have a central
server? But very interested in all developments in this field. For CRDTs, I
generally see research papers and prototypes, but not much production-ready
libraries, etc.

It sounds awesome, though I’m short on time currently (I’m much more free during holidays ^.^).

The first.[quote=“houshuang, post:7, topic:9736”]
If it’s the first one, I think a bigger concern is the
number of websockets that can be connected to a ShareDB instance at a time,
not so much what they are doing (we haven’t really found this to be a
bottleneck at least).
[/quote]

That’s better. I believe I’ve seen some benchmarks that show that Cowboy and Phoenix are probably better than Node at holding many connections.

To me it’s not a question of being “necessary”, it’s just that they’re much easier to understand usually xD Performance characteristics in a client-server architecture probably lag behind OT in all metrics (the memory and network overhead of all CRDTs I’ve seen for text is quite high).

My main problem with CRDTs is that it’s hard to implement an “intermediate” level of structure. Low structure, like a freeform graph? Nice, CRDTs got you covered. Text editing (editing a chain of characters), again, easy. Editing trees (and enforcing the fact that it remains a tree)? Acyclic DAGs? You’re out of luck…

@tmbb Did you start anything with this? I’m looking at ShareDB and was trying to work out if this is something I could do in reasonable time with Elixir

I’ve started something but didn’t really go very far… Indon’t have my laptop with me for christmas, otherwise I’d send you what I had…

But it’s not much anyway. There are some Elixir packages that implement parts of the solution.