I do not know a good one. A former colleague of mine is now working on a memory-mapped log-structured merge tree implementation and it can be a good alternativ

I do not know a good one. A former colleague of mine is now working on a memory-mapped log-structured merge tree implementation and it can be a good alternative. LSM provides elasticity, one can store as much data as one needs, it is static, thus it can be compressed as well as Parquet-stored data, memory mapping and implicit indexing of data do not require additional data structures. Something like LevelDB and/or RocksDB can provide most of that, especially when used in covering index [1] mode. [1] https://www.sqlite.org/queryplanner.html#_covering_indexes https://www.sqlite.org/queryplanner.html#_covering_indexes