4 months ago
We shouldn't be surprised because the writer works with both sqlite and AI but
> Here’s a polished section you can insert into your article (it fits naturally after the Sync Phase section):
4 months ago
I sincerely apologize for that. I am not a native English speaker, so I always use LLM to polish my articles before publishing.
4 months ago
My problem with this kind of design is that you can't really use any relational constraints. Or constraints between columns in a given table because each column is independently merged
4 months ago
I wonder if a columnar database like DuckDB might be better suited for CRDT Local-first solutions, using batched writes to mitigate
4 months ago
For a primer on CRDTs, Martin Kleppmann has a number of good videos: https://www.youtube.com/watch?v=x7drE24geUw
4 months ago
This works assuming everyone has the same clock or performs changes causually distant from each other. It fails to work if, say, 1000 people all make a change around the same time. This also applies to lamport timestamps.
4 months ago
If a thousand people all made a change at the same time in a totally deterministic, always online system a single one of those writes would arbitrarily win in exactly the same way.
In practice "1000 people edit same thing at same time" is not a problem that needs to be solved via software, the users are just doing silly things and getting silly results.
4 months ago
If it isn’t handled correctly, you’ll eventually end up with parallel histories on different devices. Even if it isn’t 1000 people, people will share documents with entire classrooms, offices, etc., which increases the probability of this situation tremendously.
4 months ago
We handle this in Fireproof with a deterministic default algorithm, in addition to having a hash-based tamperproof ledger of changes. Fireproof is not SQL based, it is more like CouchDB or MongoDB, but with cryptographic integrity. Apache 2.0 https://use-fireproof.com
In practice during CouchDB's heyday, with lots of heavy users, the conflict management API almost never mattered, as most people can make do with deterministic merges.
4 months ago
4 months ago
CRDTs only care that the end result is eventually the same.
It doesn't need to make sense, or be the most recent change, only that given the same inputs, everyone independently agrees on the same output.
4 months ago
We are saying the same thing. I was pointing out that the article missed one of the hardest parts of actually implementing this, where your algorithm architecture can totally fuck you over if you didn’t plan for it. I just think it’s interesting that they missed pointing it out. Either they got it right on the first try or they haven’t realized the issue with the schema they’re proposing.
4 months ago
Yeah, I implemented a vector clock a few years ago, and I never really found an elegant way to deal with conflicts like this. My very-much-inelegant solution was every item attached an epoch time in milliseconds which was used in a tiebreaker, and if both timestamps were the same I would hash something and choose the smaller one of those.
It seems wrong to rely on NTP for a distributed system like this, but I couldn't really figure out a better way at the time.
4 months ago
The most elegant solutions is to look at Lamport’s other papers, like Paxos or their derivatives. Tie-breaking doesn’t actually happen at the clock level, but at the conflict resolution level, which is a bit higher. IIRC, paxos traditionally uses the node id as the tie-breaker, making leadership deterministic in the face of conflicts.
Though in all honesty, NTP is mostly fine for datacenter deployments where clocks are usually within nanoseconds of each other, so you can use a timestamp with microsecond precision and probably be fine.
4 months ago
The algorithm has a way to resolve conflicts even if, by any chance, the Lamport clock has the same value in all peers
4 months ago
Yeah, but the fact that they didn’t even mention it in their post is why I brought it up.
4 months ago
Isn’t this just vlcn’s crsql?