I can only imagine what the team at Realm is thinking after going through comments and the post-mortem. Realm was an open-source mobile first database for the past 3 years. It's free. Its the most correct, consistent, and simple mobile database that is running on millions of devices (Yup fine, kind of my opinion but trust me mobile community will back this up). They ship FAST, they ship real USECASES. They just recently entered the cloud space with their Mobile Database Platform, and they are even experimenting with new things like a version built for Node.js.
I'm honestly not trying to make a specific point, but asking more questions... Is mobile different? Is it easier? Are mobile developers more willing to try new technology? Are they more willing to pay for technology? (Realm is free, haven't paid them a penny, so not sure about this one...)
My main point I guess is that it's not a terrible market, Realm made it work with VERY similar ideals and goals. So what else is going on here?
Yes, mobile in this context is very different. Or rather, local is very different. Building a database that resides on a local device and is primarily accessed by a single user is an entirely different class of problem than one that is on a server. Usually most of the hard problems in building a database system involves dealing with multiple people accessing or modifying data at the same time. When you have a single user, that problem either disappears or is massively reduced.
As you said, Realm does appear to have a server offering now, but from the sounds of it, it hasn't really been proven yet, so I don't think it's as easy as saying they've succeeded where Rethink failed.
He details why they put marketing and shipping first with constant improvements on correctness or security. On top of this, I advise just embedding the benefits into the product & designing it for easy change so components can be replaced once big revenue comes in. As development pace slows, QA pace can increase on components stabilizing.
They've raised a roughly similar amount of VC money as RethinkDB did. Their last raise was a few years ago, before Parse's shutdown, so I suspect that investors are more antsy about this space today.
The fact that Realm recently entered the cloud space sounds similar to RethinkDB's trajectory too... Of course I hope Realm makes it, it's a great product. But I'm worried that they're trapped in the VC-funded model like RethinkDB was.
It's easier to get adoption for mobile, I'd think.
Database component designed for use by mobile applications: something you base an app around
Database server: something you base your business around
Furthermore, mobile is becoming in-demand or even core in both consumer and enterprise. For enterprise especially, though, you have to think of it as mobile + sync, not on-device only.
Turns out sync is the really hard part when you want to build something that's robust in the face of poor network connectivity.