I've looked on FoundationDB and on paper it looks great. But it never got momentum, like, say, MongoDB. Is this just a matter of hype or it is not that great as advertised?
It is difficult to use by itself: the "foundation" in the name describes it quite well. It is a foundation that you build a database on. It fits my use case very well, for example, because I know my data model and usage patterns very well and I can integrate deeply with the database, but it's not a good match by itself for quick-and-dirty apps.
It provides fantastic (strict serializable) consistency guarantees in a distributed database, which is extremely rare. It is a huge advantage, but sadly most people do not understand how badly most distributed databases are broken and don't even understand the concepts (https://antithesis.com/resources/reliability_glossary/) well enough to talk about the issues involved. See every discussion where someone mentions ACID.
It's hard to compete for mindshare when the concepts are difficult and every other database has a warm-and-fuzzy-feeling website saying that everything will be great (it usually won't).
Personally, I hope more people will start using it, and I hope to see more easy-to-use databases built on top of it (that's what it was designed for, really). In my experience with it, working with a fast distributed database that gives you strict serializable semantics right in your code is fantastic.
FoundationDB started development in the same year MongoDB launched but took nearly four years to reach the market. It's the rarely discussed dark side of great testing - you can end up with robust code nobody cares about because it arrives years after people decided they wanted it. Everyone went with what existed and learned to deal with its quirks. In this case they got lucky I guess that Apple saw the potential for iCloud and bought them out, but the people who had bet on FDB before then kinda lost. You really don't want your database to be bought and made fully private tech. MongoDB was open source at the start and went closed later but never disappeared, so whilst the license switch pissed people off it didn't fundamentally wreck MongoDB as a viable tech.
Database tech has a chicken and egg problem. Most people don't want to run their own infrastructure anymore. No clouds offer hosted FoundationDB, so people don't want to use it for that reason, which means there's no demand, so clouds don't offer it, ad infinitum. MongoDB was released around the start of the cloud era, just three years after AWS first launched, so that was less of an issue. Back then "cloud" just meant VMs and storage. And later Mongo built their own cloud offering.
FoundationDB does full strict serializability checks, which is expensive. One trick it uses to get acceptable performance is by imposing a difficult programming model on the user. Keys and values must be small. Think individual fields of a JSON object, not objects themselves. Transactions also have very small limits in lifespan and size. You can't open a transaction and run a computation against your entire dataset in FoundationDB unless it's tiny. Everything has to complete in five seconds or else your transaction dies.
Their website used to claim this timeout isn't even configurable, it's hard to know if it changed because the FoundationDB team at Apple don't care about marketing. Probably Apple don't care if anyone else uses it and only made it open source to make the team happy. Even quite average open source projects have better marketing. Their blog consists only of release announcements and the last one was in 2022. A casual visitor who didn't know better would think it had been abandoned years ago.
The scalability story is unclear. It doesn't matter for most people but the biggest FDB clusters are about 100T in size. Apple say they use it for iCloud but really they use a large fleet of FDB clusters with lots of in-house tooling for balancing and moving data between those clusters. Effectively they built another scaling layer on top of core FDB.
Even if you work through all of that, what you get is a key value store. Not really a database, it's more like the bottom layer of a database. That's why it's called FoundationDB. It's not meant to be used directly. There are layers that turn your actual data into key/value pairs in a way that offers features like schema handling, object serialization etc but they are language specific and not so well documented. Most devs on the backend will have ORMs or frameworks they already want to use, and Apple server-side is mostly a Java shop so there's a Java layer, but you can't just point Spring at an FDB cluster and go. For instance, there's no notion of a query, or a query planner or even indexes. You're expected to handle all that stuff using libraries in your app.
So overall it's a highly solid bit of tech that solved a very small, very specific problem very well but years too late for anyone to care. Except for Apple. Good work, whichever Apple executive sponsored that deal!
This is a fantastic summary and the only thing I would add is that FDB was publicly available only for a year and a half before Apple bought and close sourced it. There was simply not enough runway for the hype to develop. By the time it was open sourced again four years later, the world had moved on and FDB was something of a curiosity from the past, a what-could-have-been story.
> something of a curiosity from the past, a what-could-have-been story
This is what I find bizarre: one would think that engineers would take a rational approach and look at technical merit rather than follow hype.
Technically today FDB is state of the art, it's really hard to point to any distributed database that gives you strict serializable semantics and versionstamps (these are very flexible and a great tool to implement things like changefeeds).
But I agree that being bought by Apple killed the momentum and some people don't realize it's been open-sourced since.
