At this point, we are in logs three levels deep—we have a database with a log-structured merge tree, we have a journaling filesystem like ext4, and we have an SSD controller which uses log structures internally for wear leveling.

I recommend the paper, “Don’t stack your Log on my Log”:

https://www.usenix.org/system/files/conference/inflow14/infl...

Basically, the beautiful thing about log structures is that they work well on “dumb” storage. Paradoxically, when you put logs on top of logs, you can make things worse. This is unintuitive, but it reminds me of the fact that if you tunnel a TCP connection over another TCP connection, the result is something which is much less reliable than an ordinary TCP connection operating over an unreliable network.