Most database schemas at Google have exactly two "columns": a primary key column, and an "Info" column which contains a large protobuf. The difference between that and a simple K/V store, though, is that the storage engine is building indices and columnar data stores under the hood that make it perform as if it had been defined with all the fields as flattened columns, but you never actually have to declare a schema in any detail. That cuts down dramatically on tooling and release nonsense - there's nothing like a Rails migration script, because the only update you're likely to do is "sync to latest proto definition". It also means that you have all the semantics of a protocol buffer to define your data structure - oneofs to express optionality, and submessages to group fields together - which simply don't exist in a normal DBMS.