Performance issue updating node last reports

[sodabrew]

This is well and truly bizarre and causes report pruning to take a very long time:

mysql> select * from reports where node_id = 2099 and kind = 'inspect' order by time desc;
Empty set (0.00 sec)

mysql> select * from reports where node_id = 2099 and kind = 'inspect' order by time desc limit 1;
Empty set (3.16 sec)

Ah, it's triggering MySQL to use the wrong index:

mysql> explain select * from reports where node_id = 2099 and kind = 'inspect' order by time desc;
+----+-------------+---------+------+--------------------------+--------------------------+---------+-------+------+-----------------------------+
| id | select_type | table   | type | possible_keys            | key                      | key_len | ref   | rows | Extra                       |
+----+-------------+---------+------+--------------------------+--------------------------+---------+-------+------+-----------------------------+
|  1 | SIMPLE      | reports | ref  | index_reports_on_node_id | index_reports_on_node_id | 5       | const | 1682 | Using where; Using filesort |
+----+-------------+---------+------+--------------------------+--------------------------+---------+-------+------+-----------------------------+
1 row in set (0.00 sec)

mysql> explain select * from reports where node_id = 2099 and kind = 'inspect' order by time desc limit 1;
+----+-------------+---------+-------+--------------------------+----------------------------------------------+---------+------+------+-------------+
| id | select_type | table   | type  | possible_keys            | key                                          | key_len | ref  | rows | Extra       |
+----+-------------+---------+-------+--------------------------+----------------------------------------------+---------+------+------+-------------+
|  1 | SIMPLE      | reports | index | index_reports_on_node_id | index_reports_on_time_and_node_id_and_status | 782     | NULL | 1073 | Using where |
+----+-------------+---------+-------+--------------------------+----------------------------------------------+---------+------+------+-------------+
1 row in set (0.00 sec)

(This is MySQL 5.5.35)

[bwitt]

I'm going to call this a bug in MySQL 5.5.35; please re-open if this is not the case!