> All the data is one MySQL table This is not correct at all. Facebook has many distinct MySQL tiers (distinct sets of shards) supporting different purposes.

> All the data is one MySQL table This is not correct at all. Facebook has many distinct MySQL tiers (distinct sets of shards) supporting different purposes. And each tier has many tables. The UDB tier (user database / primary product backing store) had several hundred tables when I worked on Facebook's MySQL team 7+ years ago. This was before the MyRocks migration though, and it's possible the UDB layout changed to reflect MyRocks' extensively different file layout vs InnoDB. But in any case, especially keeping in mind all the various distinct tiers, saying all data at Facebook is one table is egregiously incorrect.