We add FORCE INDEX to revision because probably we have hit a MariaDB
bug that can potentially create an outage on pages with thousands of
revisions due to extreme resource usage by this query when using the
wrong index page_user_timestamp, instead of page_timestamp.
This is considered to be a hack, and once we are in the clear, I promise
to review this an try to get a saner execution path (both in MySQL and
in PHP.
Bug: T116557
Change-Id: I41853da5c0e1a15efad5594eff0cee62be1ad9a4
