Here is a story [1] about the first version of B-link optimization for Innodb that is the most used B-tree engine in MariaDB. It started from a sketch on a chocolate wrapper and after some attempts ended up with significant p95 improvement for certain B-tree operations. Thx Zhao Song for his work in this area for MySQL.
1. https://mariadb.org/from-a-chocolate-wrapper-to-concurrent-innodb-page-splits/