From a slow query to its index

What happens

A find on a nested address field returns a few dozen rows and is graded a collection scan, with every document in the collection examined to find them; the plan names the index that would fix it, the index is created from the plan itself, and the same query re-runs graded optimal at 100% efficiency.

Chapters

1. 0:00 Open orders
2. 0:04 A find on a field inside the shipping address
3. 0:18 The grade was collected for you
4. 0:21 Collection scan: every document read to return thirty
5. 0:22 Open the whole plan
6. 0:25 And it names the index that would fix it
7. 0:30 Build it
8. 0:35 Same query, again
9. 0:39 Same rows, and the grade has turned
10. 0:43 And the plan agrees