Explicit Schema Normalised or semi normalised structure JOINs to retrieve related data Implicit Schema Embedded structure Related data retrieved naturally with object
Comparison (never trust benchmarks) Loading 1.2 million records PostgreSQL MongoDB 76 sec 8 min Sequential scan PostgreSQL MongoDB 980 ms 980 ms Index scan (Postgres GINhash) PostgreSQL MongoDB 0.7 ms 1 ms
General Advice Write heavy → Fewer indexes Read heavy → Denormalise Keep large data away from read/write heavy data Blob stores/filesystems are DBs too