A K-V store by construction has an index (over K). But you seem to also want referential integrity and transactions, not small features, limiting the implementa

A K-V store by construction has an index (over K). But you seem to also want referential integrity and transactions, not small features, limiting the implementation quite a lot. You can attain what you desire by using an RDBMS, and having all tables with one key column, and a TEXT column with your serialized non-key fields; it's going to be a fun approximation of 6NF. Realistically, you can have all joinable columns as normal columns, indexed as you desire, and the rest of the columns as a serialized blob. When you want high parallelism for guaranteed independent segments of data, use sharding.