Ask HN: Embedded Database Design Papers

In order to learn more about database design principles I thought it would be great to read papers on embedded databases. I have searched around for material on the popular open source databases like RocksDB, LMDB, or LevelDB but haven't found anything concrete. Aside from reading the source code, how can I teach myself about the data structures and abstractions that these provide? Eventually I would like to write a toy implementation after getting acquainted with a subset of this knowledge.