We have a query on the revision table which has an explicit FORCE INDEX page_timestamp that was added after the investigation at T116557, a few years ago, since the query was filesorting.
I'm not entirely sure that forcing the index is still necessary. Perhaps this is because MariaDB was updated, or maybe some change to the revision table; for instance, during the actor migration the page_user_timestamp index (previously chosen by the optimizer) was replaced with rev_page_actor_timestamp. Below is a test in prod, but I'd like DBAs to confirm.
New EXPLAIN for T116557#3204852:
daimona@mwmaint1002:~$ mwscript mysql.php --wiki=enwiki wikiadmin@10.64.16.186(enwiki)> EXPLAIN SELECT /* AFComputedVariable::{closure} */ * FROM `revision` WHERE rev_page = '1743794' ORDER BY rev_timestamp DESC LIMIT 100\G *************************** 1. row *************************** id: 1 select_type: SIMPLE table: revision type: ref possible_keys: page_timestamp,rev_page_id,rev_page_actor_timestamp key: page_timestamp key_len: 4 ref: const rows: 192464 Extra: Using where 1 row in set (0.01 sec) wikiadmin@10.64.16.186(enwiki)> SELECT version()\g +---------------------+ | version() | +---------------------+ | 10.4.18-MariaDB-log | +---------------------+ 1 row in set (0.00 sec)