Well, operational dbs in practical circumstances are used for queries that take predictable time to complete. "Get a row" "Get ten rows" Etc, etc. All constan

Well, operational dbs in practical circumstances are used for queries that take predictable time to complete. "Get a row" "Get ten rows" Etc, etc. All constant, all predictable, all not requiring unpredictable time to run. Also caches nicely. What is "simply wrong" here?