R1:3391e3d34b10

Use (a = ? AND b = ?) instead of (a, b) IN (?, ?)

Summary: MySQL is not able to use indexes with searching for tuples.

Test Plan:
Explained the query before and after, saw `key_len` 16 instead of 8.
Also saw time 0.0 s instead of 2.9 s (but that was probably caused by warming up).

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5580