[evanelias]

> They removed foreign keys from mysql

This isn't specific to Meta/Facebook in any way. A very large percentage of big tech companies use MySQL without foreign key constraints, because they're problematic at scale.

To be clear, foreign key constraints are not used, but it's still very much a relational use-case / workload.

> using it as a column store db

That's nonsensical. Column stores are for analytics, whereas MySQL is used for OLTP. Both InnoDB and MyRocks are row-oriented storage engines.

Maybe you actually meant "key-value store", which is a more common claim, but that's still completely wrong. The query pattern for Facebook's social graph relies heavily on range scans over indexes, which isn't a concept supported by key-value stores. And there are many MySQL workloads at Facebook outside of the social graph database tier, with extremely varied use of MySQL functionality.