Facebook Engineering 發了一篇將 MySQL 升級到 8.0 的說明：「Migrating Facebook to MySQL 8.0」。
先前的版本主要是 5.6，加上 MyRocks：
Our last major version upgrade, to MySQL 5.6, took more than a year to roll out. When version 5.7 was released, we were still in the midst of developing our LSM-Tree storage engine, MyRocks, on version 5.6. Since upgrading to 5.7 while simultaneously building a new storage engine would have significantly slowed the progress on MyRocks, we opted to stay with 5.6 until MyRocks was complete. MySQL 8.0 was announced as we were finishing the rollout of MyRocks to our user database (UDB) service tier.
在 GitHub 上是有 facebook/mysql-8.0，但看起來從 2017 後就沒更新了，所以應該是沒有 open source 出來。
看看就好 XD