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Comment by mike_hearn | Hacker News Reader

That's basically right except it's worth noting the belief that RDBMS can't scale horizontally is wrong. Most RDBMS engines can't do that, but an example of one that can is Oracle. RAC clusters scale write masters horizontally up to fairly large cluster sizes (e.g. 32 write masters works OK) and obviously read replicas can be added more or less indefinitely.

RAC isn't sharding. The Oracle JDBC drivers do support automatic sharding across independent databases or clusters too, but RAC is full horizontal scaling of full SQL including joins.

It's also worth noting that if your Ruby app is CPU constrained you could take a look at TruffleRuby. It runs on the JVM, has a full JIT compiler more powerful than YJIT, can deal with native modules, and doesn't have a global interpreter lock (threads do really run in parallel).

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This is what I mean when I say Oracle's DB product is actually pretty good. Say what you will about Oracle the company, but their core products are good at their respective domains.

Yeah there's a lot of other neat tricks you can do with it. Someone else in this thread observes that a major issue for most Rails apps is latency. Loading a page does 100 blocking queries serially which means 100 roundtrips (minimum), the latency from that adds up and before you know it your fast computers are taking seconds to render a page.

Although it often gets lost inside app frameworks, you can use the Oracle drivers to dispatch every query at once in one request, or even just execute a stored procedure that has all the queries for a page registered inside the DB then work through the results from each query client-side. So you can really optimize the latency heavily if you can structure your app in such a way that it can exploit such things. JDBC supports this for instance but Active Record doesn't.

My favourite DBs are Oracle and SQL Server, and no FOSS religion is going to change my mind.

Too many folks lose on great technology because of hating the man, 70's hippie style.

And yes, I have used Postgres and MySQL and such.

It is similar to all the programming languages that have never moved beyond raw command line and basic editor tooling, only better nowadays, because of Microsoft (that they hate) making VSCode (driven by Eric Gamma of Eclipse fame), and LSP a common thing for all workloads.

>My favourite DBs are Oracle and SQL Server, and no FOSS religion is going to change my mind.

I mean even mentioning MySQL is better than Postgres in some areas is not even welcomed on most of the tech internet including on HN. MySQL reached 9.0 after so many years and its news doesn't even reached HN's front page.

>Too many folks lose on great technology because of hating the man, 70's hippie style......... It is similar to all the programming languages

And It is not just PL. It is pretty much all across tech spectrum, and even beyond tech. I am a tech enthusiasts, not an PL, Editor, DB enthusiasts. We should be able to admit Oracle and SQL Server are better now but we strive to make similar if not better DB that is open source.

Due to Amdahl's law, you surely don't get 32x write throughput from having 32 write masters however.

It depends a lot on what the query patterns are. If your writes are naturally spread out then yes you can get close because the 32x will be writing to 32 different parts of the database and there won't be cache blocks pingponging around. If all the writes are contending on the same parts of the same tables then you won't get 32x indeed because your queries will be waiting on each other to release locks etc.

At least that's my understanding. I've not tuned an app that runs on such a cluster.

Amdahl's law doesn't talk about throughput, but latency. You can absolutely get 32x more throughput by having 32 parallel backends. Each individual write won't be 32x faster e2e, but that's not really the point.

But what about when multiple nodes have to coordinate to do a write?

Even 10y ago MySQL Galera Cluster was providing pretty good write scalability. (Without the need for PhD in Oracleolgy, and without donating your kidney to Larry.)

CockroachDB can too, although its licensing has made it unpopular.

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