[nine_k]

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.

[mr_toad]

FoundationDB supports referential integrity and indexes in a layer on top of the key value store.

https://apple.github.io/foundationdb/layer-concept.html