I have used Kotlin a bit for a hobby project and it felt like they were 95% done with a 1.0 version. I love the promise of a single code base that can run on the JVM and browser, but it is not all there. Until recently, the API was not guaranteed to be stable. Every one in a while, I hit a feature that is JVM only or does work right in JavaScript. The JS compiler will "helpfully" remove uncalled public functions unless you explicitly mark them with JsExport.
Also, from what I can tell, only InteliJ is the only supported IDE (which makes sense, since they are the language developers). There is an official Eclipse Plugin, but the last time I tried it, it did not work and tried to take the entire IDE down with it.
Having said that, it was very close to complete and I have not worked on that project for a few months, so it could all be perfect now.
The point of using a cache is to have data in memory and not on disk. From what I can tell, Postge Unlogged tables are still written to (and read from) disk. It is just that the write is done in an unsafe way.
The article explains how one would go about benchmarking performance but forgets to actually include performance metrics. Luckily they link to another write up that does. Using an Unlogged table vs. a regular table reduces write times about 45% and gives you about 3 times as many transactions per second. It is not nothing but it is probably not worth the code complexity vs. writing directly to a persistent table.
Even the "no persistence" behavior of a cache is not strictly true: an unlogged table is only truncated if Postgre is shut down unexpectedly (by kill -9 the process or by killing the VM). If you restart if you shut down the process in a controlled manner, the unlogged table is properly persisted and still has data when it starts.