CRDT and SQLite: Local-First Value Synchronization

51 pointsposted 4 days ago
by marcobambini
(marcobambini.substack.com)

10 Comments

philsnow

3 hours 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):

withinboredom

4 hours 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.

p1necone

2 hours 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.

withinboredom

2 hours 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.

jchanimal

17 minutes 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.

ncruces

2 hours 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.

withinboredom

an hour 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.

marcobambini

4 hours ago

The algorithm has a way to resolve conflicts even if, by any chance, the Lamport clock has the same value in all peers

withinboredom

4 hours ago

Yeah, but the fact that they didn’t even mention it in their post is why I brought it up.