I am lucky enough to have worked on all three of these systems (TAO, ZippyDB, and currently MySQL) so can shed some light here.

Both MySQL and ZippyDB are datastores that use RocksDB under the hood, in a slightly different way and with different querying capabilities exposed to the end user. ZippyDB uses it exclusively, but MySQL uses both the traditional InnoDB and RocksDB (MyRocks). TAO is in memory graph database, layer above both of these, and doesn't persist anything by itself - it talks to the database layer (MyRocks).

Author here.

> Well written article

Thanks!

> It is not Tao it is ZippyDb

I don't work for Meta, so might have made a mistake. There is an old blog post[1] about Tao and there is a recent paper[2] mentioning that the graph database is powered by MyRocks, which runs on RocksDB.

[1]: https://engineering.fb.com/2013/06/25/core-data/tao-the-powe...

[2]: https://www.vldb.org/pvldb/vol13/p3217-matsunobu.pdf

rocksdb is used in many more systems, but the storage layer behind TAO (UDB) is using MyRocks for quite a few years by now - migration was done in 2016 or so - https://engineering.fb.com/2016/08/31/core-data/myrocks-a-sp...

Zippy does use it, but I think the author was specifically referring to MyRocks

https://myrocks.io/