Actually RDBMS queries are quite fast. But those systems weren't designed for use patterns which serverless applications typically have. Like MySQL will limit y

Actually RDBMS queries are quite fast. But those systems weren't designed for use patterns which serverless applications typically have. Like MySQL will limit you on connection count and each new connection puts extra overhead on the server. So if every function negotiates its own connection you might eat away DB resources just on negotiating connections even though the DB queries were fast.