> mostly backed by hundreds of thousands of Mysql instances
Kind of. It's part of the recipe but one you find at these large tech companies (I've worked at FB and GOOG) is they have the resources to bend even large/standard projects like MySQL to their will, while ideally preserving the good ideas that made them popular in the first place. There are wrappers/layers/modifications/etc that eventually evolve to subsume the original software, such that is acting more like a library than a standalone service/application. So, for example, while your data might eventually sit in a MySQL table, you'll never know, and likely didn't write anything specific to MySQL (or even SQL) to get there.
What you're describing sounds like you mean something on the level of Cockroach, talking the Postgres wire protocol but implemented entirely independently underneath (which came indirectly out of Google). Facebook's MySQL deployment sounds more like a heavily-patched-but-basically-MySQL installation. I think Facebook is overanalogised to Google sometimes, as an engineering org.
(Admittedly I haven't worked at either whereas you have - though I have at another FAANG fwliw - but am basing this impression partly on what I hear from friends & partly on plain old stuff I read on the internet.)
FB uses mysql in two very different ways - for the giant social-network database, mysql is basically a key-value store used as the storage layer for the graph database built on top. Then for the thousands of small utility databases (small enough to fit on a single machine) it’s used in a very vanilla way.
Kind of. It's part of the recipe but one you find at these large tech companies (I've worked at FB and GOOG) is they have the resources to bend even large/standard projects like MySQL to their will, while ideally preserving the good ideas that made them popular in the first place. There are wrappers/layers/modifications/etc that eventually evolve to subsume the original software, such that is acting more like a library than a standalone service/application. So, for example, while your data might eventually sit in a MySQL table, you'll never know, and likely didn't write anything specific to MySQL (or even SQL) to get there.