There's some info on MyRocks here: https://engineering.fb.com/2017/09/25/core-data/migrating-a-database-from-innodb-to-myrocks/ https://engineering.fb.com/2017

There's some info on MyRocks here: https://engineering.fb.com/2017/09/25/core-data/migrating-a-database-from-innodb-to-myrocks/ https://engineering.fb.com/2017/09/25/core-data/migrating-a-... Of note is that it halved the storage requirements for the user DB tier. That's a pretty big win. As for why MySQL persists: I no longer work at FB so I'm not up to speed on the current thinking but one thing to remember is that TAO isn't the only thing that talks to MySQL. The web tier itself still has (or had) data types that were backed by MySQL and memcache. Lots of other systems for data processing, configuration, and so on stored data in MySQL. Replacing all of that would be a huge undertaking. I doubt there's a 10% win laying around just waiting for the taking with all this work, especially after MyRocks rolls out. Also note that MySQL isn't the only storage system at Facebook. There are several others that were specifically written for specific use cases (e.g. ZippyDB, https://engineering.fb.com/2021/08/06/core-data/zippydb/ https://engineering.fb.com/2021/08/06/core-data/zippydb/).