liveblocks VS reference-crdts

Absolutely! The real complexity comes from conflict resolution. If someone edits the top, and someone else edits the bottom, which version do you go with? What if they're editing the same area? Entire companies exist to provide elegant solutions to this[0], so it's no simple task.

0: https://liveblocks.io/

I can imagine, browser extensions are a pain in the butt. Are you planning to open source the code? Did you build everything by yourself or on top of https://liveblocks.io/?

For the following example, I want the gradient color to flow from "Hello World" to the "Circle", so they are synchros and match the colors. I created this snippet but I'm having trouble with the rest. https://play.tailwindcss.com/accHTivCcx. Another example would be the https://liveblocks.io/'s title, which flows through the colors in the gradient. How would I achieve this?

Does anyone have any opinions about using Liveblocks for a live collaboration application as opposed to just using Firebase?

liveblocks is great for multiplayer state sync. i was able to make my canvas redux app collaborative in a couple of hours https://liveblocks.io

Very cool use case for CRDTs! I've seen a bunch of different use cases from other products like https://liveblocks.io/ and https://electric-sql.com/. It's interesting how CRDTs are now taking hold so much for all these collaborative syncing scenarios. Wonder what's driving the proliferation now given they've been around for awhile?

Hi Tim,

I'm a bit biased but https://liveblocks.io is great for that :)

If you know how to use React, that's pretty much all you need to know. It also includes some nice hooks to enable things like multiplayer undo/redo and live cursors.

The team even put a couple of interactive blog posts about that that you might find interesting:

True! I would also include https://liveblocks.io to that list of services that help developers make multiplayer experiences.

Interesting to see more players in this space to help more and more developers do this.

> 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.

Argh not getting this stuff right is really frustrating. I've been working on collaborative editing for over a decade now, and I still can't implement any of these algorithms correctly without the help of a fuzz testing. But fuzz testing done right finds all of these problems! There's no excuse!

Fuzzers work so well here because all of these algorithms have a clear correctness criteria: After syncing, state should always converge to the same result. So its pretty easy to write code which does this in a loop:

1. Generates some random changes on some fake "peers"

2. Picks 2 peers at random and sync their changes, using your new fancy synchronization algorithm

3. Assert that the state has converged between the peers

I've been working on this stuff for over a decade. I've implemented dozens of these algorithms. And every single time I write a fuzzy boi to check my work I find convergence bugs. Playing whack-a-mole with a fuzzer is a rite of passage for implementing systems like this.

When your fuzzer runs all night, you should never have lingering convergence bugs like you're describing with Word.

As an example, here's a simple fuzzer for a reference list CRDT implementation: https://github.com/josephg/reference-crdts/blob/9f4f9c3a97b4...

The code is so small it almost fits on my laptop screen.

> In this case, the bottleneck at 9 million LoC is not CPU cycles but memory usage. That's where I am considering pushing down into WebAssembly

How often does this come up in practice? I can't think of many files I've opened which were 9 million lines long. And you say "LoC" (lines of code). Are you doing syntax highlighting on 9 million lines of source code in javascript? Thats impressive!

> I guess my point is why do you need balanced trees? Is this a CRDT specific thing? Can you implement CRDT with just an array of lines / gap buffer?

Of course! Its just going to be slower. I made a simple reference implementation of Yjs, Automerge and Sync9's list types in javascript here[1]. This code is not optimized, and it takes 30 seconds to process an editing trace that diamond types (in native rust) takes 0.01 seconds to process. We could speed that up - yjs does the same thing in 1 second. But I don't think javascript will ever run as fast as optimized rust code.

The b-tree in diamond types is used for merging. If you're merging 2 branches, we need to map insert locations from the incoming branch into positions in the target (merged) branch. As items are inserted, the mapping changes dynamically. The benchmark I've been using for this is how long it takes to replay (and re-merge) all the changes in the most edited file in the nodejs git repository. That file has just shy of 1M single character insert / delete operations. If you're curious, the causal graph of changes looks like this[2].

Currently it takes 250ms to re-merge the entire causal graph. This is much slower than I'd like, but we can cache the merged positions in about 4kb on disk or something so we only need to do it once. I also want to replace the b-tree with a skip list. I think that'll make the code faster and smaller.

A gap buffer in javascript might work ok... if you're keen, I'd love to see that benchmark. The code to port is here: [3]

> Undo support -> In which case, you only have to stack / remember the set of commands and not have to store the state on every change. I'm not sure if this overlaps with the data structure choice, other than implementation details.

Yeah, I basically never store a snapshot of the state. Not on every change. Not really at all. Everything involves sending around patches. But you can't just roll back the changes when you undo.

Eg: I type "aaa" at position 0 (the start of the document). You type "bbb" at the start of the document. The document is now "bbbaaa". I hit undo. What should happen? Surely, we delete the "aaa" - now at position 3.

Translating from position 0 to position 3 is essentially the same algorithm we need to run in order to merge.

> I was just looking into TypedArrays.

I tried optimizing a physics library a few years ago by putting everything in typedarrays and it was weirdly slower than using raw javascript arrays. I have no idea why - but maybe thats fixed now.

TypedArrays are useful, but they're no panacea. You could probably write a custom b-tree on top of a typedarray in javascript if you really want to - assuming your data also fits into typedarrays. But at that point you may as well just use wasm. It'll be way faster and more ergonomic.

[1] https://github.com/josephg/reference-crdts

[2] https://home.seph.codes/public/node_graph.svg

[3] https://github.com/josephg/diamond-types/tree/master/src/lis...