As of MongoDB 2.6, background index creation will occur on secondaries as well as the primary when a background index is created on the primary of a replica set.
Lecture Notes In this video, Dwight uses the ensureIndex command, which is now deprecated. You would now use createIndex.
Quiz
Quiz: Unique Indexes
If an index is created with the options document,
{ unique : true }
can 2 documents which do not include the field that is indexed exist in the same collection?
Yes
Lecture Notes
In this video, Dwight mentions that the index is used automatically if it is present. This is no longer always true if you are sorting using a sparse index, but remains true otherwise. He also uses the ensureIndex command, which is deprecated as of MongoDB 3.0 in favor of createIndex
Quiz: Index Notes
A MongoDB index can have keys of different types (i.e., ints, dates, string)
1.True
2.False