CMU 15-721 Advanced Database Systems
Andy Pavlo’s graduate course on modern database internals, free on the course site with all lectures on YouTube.
This is the in-memory, multi-core, storage-engine end of the subject: MVCC, lock-free indexes, query compilation, vectorised execution, columnar layouts. Not “how to use Postgres” - how the thing is built.
If you have ever wondered why an OLAP engine and an OLTP engine make opposite choices about literally everything, this is the course that answers it.
See also: