Comment by timssopomo
2 days ago
Spacetime sounds like really interesting technology, but I'm not sure that the comparison between CRDB is a good one.
I used to work at Cockroach Labs. The problem it's solving is fundamentally different. CRDB as a solution makes sense when you need to _guarantee_ that transactions are serializable and durable, and that your application can survive node or region failures while maintaining consistency. In a naive deployment it's significantly slower than operating on a single core, but that's the price that you pay for the ability to survive node loss without data loss.
I don't see anything that indicates how spacetime solves the core problem CRDB does, which is guaranteeing that single node failures can be tolerated with zero data loss or loss of availability. It sounds like transactions by default are required to be written to disk before completion, which makes them durable on a single node, but you can't ensure they're consistent across nodes without accepting the network overhead and losing transaction throughput (on writes, anyway).
Also, FWIW, in the several years I worked covering basically every incident, I can't recall seeing a network-bound cluster. Like anything else, there are tradeoffs. You give throughput, you get consistency and availability, and you don't need to engineer how to avoid data loss or availability with node failures. Unless I'm misunderstanding, spacetime is solving a totally different problem.
> It sounds like transactions by default are required to be written to disk before completion
They are yolo mode by default with periodic fsync and a big mutex around every reducer: https://strn.cat/posts/spacetime/ (granted things may have changed since that blog post)
> I can't recall seeing a network-bound cluster
I saw some of these (most packets per second not bandwidth) in the Firebase Realtime Database because changes get broadcast to many users. Since SpacetimeDB is made for games this is the same synchronization effect. Traditional databases don’t do this which is why Cockroach wouldn’t have seen it.
I concede that we do have a big lock. But that is only because we did the alternative first and it performed worse, which is what OPs article is about.
Reposting what I posted below regarding the strn.cat article:
I'm a cofounder of SpacetimeDB (and the author of OPs article). The https://strn.cat/posts/spacetime/ article has several substantial errors. I've spoken with Vicent directly about them.
Most notably, almost the entire commentary about durability is incorrect. SpacetimeDB does not acknowledge anything before data is fully persisted to disk, even though he claims it does. Clients CAN chose to listen before that, but you can do the same thing in Postgres if you want.
There is no 50 ms delay to writing to disk. The article is mostly nonsense.
Ask Claude yourself: https://github.com/clockworklabs/SpacetimeDB
He spent 15 minutes looking at our code (by his own admission), having never written a database storage engine before AFAIK, and made a pronouncement that SpacetimeDB wasn't a good database. Crazy stuff.
What happens if the disk dies?
8 replies →
Sorry for spreading misinformation!
1 reply →
> which is guaranteeing that single node failures can be tolerated with zero data loss or loss of availability
We solve this with distributed state machine replication. You don't need multiple writers to solve the single node failure problem. You only need multiple writers for a write throughput scaling problem.
They're separate problems.