Like S3 or Redis, RocksDB is much more performant when you don't need the query engine and want to have highly compact storage with fast lookups and high write

Like S3 or Redis, RocksDB is much more performant when you don't need the query engine and want to have highly compact storage with fast lookups and high write throughput. Storage engines are different levels of complexity based on the query requirements. Simple K/V stores can run circles around Postgres/MySQL as long as you don't need the extra features.