How we built a serverless SQL database

I think some of the value of Cockroach Serverless may depend on what the RUs (request units) map to. Looking at some competitors...

Google says that Cloud Spanner should get you around 7,000 read queries per second and 1,800 write queries per second for $650/mo. If a simple indexed read is 1 RU, $650 on Cockroach Serverless would get you around 2,500 reads/second. Of course, I think it's completely reasonable for a Serverless option to cost a bit more given that you'd need to over-provision Cloud Spanner (even if you smartly increased/decreased the amount of compute allocated based on demand).

Planet Scale charges $15 per 100M rows read and $15 per 10M rows written. If an RU is a row read, then Cockroach Serverless would be $10 per 100M rows read. If a write takes 10 RUs, Cockroach would cost $10 per 10M rows written. Both of those would be less than Planet Scale's cost - but it's possible that a row read will cost more than 1 RU. Let's say that an indexed lookup of a row costs 5 RUs. Then Cockroach Serverless starts costing 3.3x more than Planet Scale.

AWS DynamoDB charges $1.25 per million write request units and $0.25 per million read request units. If I can get 10M reads from Cockroach Serverless for $1 and 4M reads from DynamoDB for $1, Cockroach's pricing looks pretty good. Of course, if I need 5 RUs to do an indexed read, the pricing doesn't look as good anymore.

I do respect Cockroach Labs somewhat ambiguous description here. Planet Scale's $15 per 10M rows written feels like something that could become bad. What if I define hundreds of indexes on the table? What if I'm inserting very large blob/text columns that are 50MB in size? Likewise, what if I index no columns and end up forcing a full table scan, but only 10 rows are returned? Do they consider that I "read" 10 rows or "read" all the rows in the table? If it's the former, I'm putting a lot of strain on their system without paying for it. If it's the latter, I'm going to just define indexes that might not be worth it if I were paying for the IO needed to do all that writing.

Still, it would be nice if Cockroach Labs offered some indication of what could be accomplished with 1 RU. "An indexed read of 1 row or an indexed read of a few rows in sequence; for example, 'SELECT * FROM people WHERE age > 18 ORDER BY age, name LIMIT 10' where there exists an index on (age, name)." That would let me know what to expect. "A write of a row under 4KB in size with no secondary indexes will cost 3 RUs; expect secondary indexes to increase the cost by 1 RU each" would give me an idea of what's going on.

I think there are definitely cases that one can't easily enumerate. For example, "UPDATE people SET age = 18 WHERE EXISTS (SELECT * FROM legacy_info WHERE people.id = legacy_info.people_id AND legacy_info.is_adult = true)". That's potentially going to require lots of stuff that's harder to predict. However, at this point I don't know if an indexed read of a row costs 1 RU or 10 RU. If an indexed read of a single row costs 1 RU, if I read 10 rows sequentially will that mean 10 RUs or will 1 RU have enough IO to cover that since they're sequential (or will the billing just over-charge since there's tangibly more rows and that's easy to explain)?

I think a decent amount of the value depends on the pricing and it's hard to judge that right now.

One thing I will note is that the storage seems expensive. It's slightly cheaper than Planet Scale, but a lot more than the $0.30/GB of Cloud Spanner or the $0.23/GB of FaunaDB or $0.25/GB of DynamoDB. I've been wondering a bit about the storage pricing of Planet Scale since $1.25/GB seems expensive. Cockroach Serverless is coming in at $1/GB which also seems expensive compared compared to alternatives. If Cloud Spanner is basically offering a third the price, is the "Serverless" flexibility worth it given that Spanner can be scaled up/down pretty easily in very granular increments.

Actually, one thing that could be useful might be noting how many request units per month one of the dedicated instances would have. A 2 vCPU CockroachDB instance costs $350-400. Would that be 4 billion request units per month (assuming you were fully utilizing the box)? Would it be more like 15 billion request units per month since you're presumably paying a premium for the Serverless flexibility?

This offering seems a lot more compelling than the serverless databases offered by AWS directly.

At least if cost and scaling to zero is important to you. Dynamodb addresses the cost issue, but it's so painful to use, and is unsuitable for a lot of use-cases. Aurora Serverless takes 30 seconds to cold-start, so it's also usually a non-starter, other than for batch type workloads.

So great work, but I have a couple of questions:

Any plans to support AWS privatelink? I played around with this a bit, and it seems you need to connect to it over the internet which isn't always ideal.

Will there be a limit on how many free databases you can create? I think there are some valid use-cases where one might want to create a bunch of them, but I would be scared to do this at the risk of being kicked off your platform for abuse.