Just saw this query that does a full scan on `echo_event` table. The particular query was captured on metawiki, but I would guess it happens everywhere.
```
root@db1127.eqiad.wmnet[metawiki]> explain SELECT /* EchoEventMapper::fetchByPage */ event_id,event_type,event_variant,event_agent_id,event_agent_ip,event_extra,event_page_id,event_deleted FROM `echo_event` WHERE event_page_id = 11831723;
+------+-------------+------------+------+---------------+------+---------+------+---------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+------+-------------+------------+------+---------------+------+---------+------+---------+-------------+
| 1 | SIMPLE | echo_event | ALL | NULL | NULL | NULL | NULL | 2525157 | Using where |
+------+-------------+------------+------+---------------+------+---------+------+---------+-------------+
1 row in set (0.001 sec)
root@db1127.eqiad.wmnet[metawiki]> select count(*) from echo_event;
+----------+
| count(*) |
+----------+
| 3669017 |
+----------+
1 row in set (1.634 sec)
```
Index missing on these wikis: T308206#7923360
[] labswiki
** [] eqiad
** [] codfw
[] mediawikiwiki
** [] eqiad
** [] codfw
[] metawiki
** [] eqiad
** [] codfw
[] officewiki
** [] eqiad
** [] codfw