Setup: create a toy collection that has no indices:
Then, start a 2.4.x mongod with the --notablescan option:
Even though --notablescan was set, 2.4 is using a collection scan. This behavior has changed in 2.6:
Although the 2.6 is definitely more logical, this is a backwards breaking change that surprised at least one user (see
SERVER-13520). We should doc this so it doesn't bite more users!