Simple example when MongoDB will be faster that Oracle: save a customer with several postal addresses.
With oracle (actually any relational database), you will:
- Initiate a transaction
- Save the customer row
- for each address, save the address row, with a reference to the customer row
- Commit the transaction.
If you have, let's say, 3 addresses, you will have 4 inserts + the transaction cost.
With MongoDB (or any NoSQL database), you will:
- Save the customer document (including its sub property Addresses)
Here, you have only one insert. No transaction required, because you only execute one atomic insert.
On equivalent hardware, I'm quite sure MongoDB will be faster that Oracle.
But the actual conclusion is not that Oracle or MongoDB will be faster, but that comparing benchmarks between Nosql and RDMBS is a non-sense, because you won't build your apps in the same manner, both worlds have pro and cons that go far beyond speed comparison