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I know two DB bibles which explain how a DB engine actually works. It's much more interesting reading than another SQL manual. But it's not awfully practical if you have no particular interest in DB technology. And both are pretty dense. * https://www.amazon.com/Database-Systems-Complete-Book-2nd/dp * https://www.amazon.com/Database-System-Concepts-Abraham-Silb...

There's a very cool not-quite-alternativE: https://leanpub.com/how-query-engines-work. It covers a fair chunk of DB technology but not storage. Definitely check out their repository at https://github.com/andygrove/how-query-engines-work/tree/mai... .

A companion to DDIA would be https://www.amazon.com/Database-Internals-Deep-Distributed-S... (especially its treatment of LSM trees which is harder to come by).