Cool. This post is right beside the 37signals one[1] that mentions SolidCache[0] "A database-backed ActiveSupport::Cache::Store".
I discovered two solutions in one day.
The advantage with kvrocks is that it supports the Redis protocol, so you can use all the drivers, tools, cluster tools for Redis.
I've used this one too. It works well.
https://github.com/apache/kvrocks
It's a Redis compatible database on top of RocksDB, so unlike Redis it uses the disk instead of RAM, but you can control how much data is cached in RAM, obviously Kvrocks will be slower than Redis for uncached data.
Useful in situations where you want a KV data store that isn't limited by your memory specs but is compatible with everything that speaks Redis.