If you are considering using plain files instead of a DB server, you could try a compromise and use an embedded key-value store like RocksDB, LevelDB, BadgerDB

If you are considering using plain files instead of a DB server, you could try a compromise and use an embedded key-value store like RocksDB, LevelDB, BadgerDB etc. It's local storage only, limited query capabilities depending on the DB, but should be extremely fast.