无法在MariaDB 10.2中解锁表

我正在使用MariaDB 10.2 . 我有一个约60M行的表 . 最初是我试图运行：

insert into signals select * from signals_tmp where signal_num = 21;

MariaDB冻结了 . 从那时起，我试图重新启动mysqld和我的笔记本电脑，所以我没有第一次冻结的确切状态 . 现在，当我尝试这样做时：

select count(*) from signals where signal_num = 20

它冻结了，所以我在MySQL中按下Ctrl C.然后我运行以下内容：

MariaDB [phd]> show open tables where In_use = 1;
+----------+---------+--------+-------------+
| Database | Table   | In_use | Name_locked |
+----------+---------+--------+-------------+
| phd      | signals |      1 |           0 |
+----------+---------+--------+-------------+
1 row in set (0.00 sec)

MariaDB [phd]> show processlist;
+----+-------------+-----------------+------+---------+------+--------------------------+----------------------------------------------------+----------+
| Id | User        | Host            | db   | Command | Time | State                    
| Info                                               | Progress |
+----+-------------+-----------------+------+---------+------+--------------------------+----------------------------------------------------+----------+
|  1 | system user |                 | NULL | Daemon  | NULL | InnoDB purge coordinator | NULL                                               |    0.000 |
|  2 | system user |                 | NULL | Daemon  | NULL | InnoDB purge worker      | NULL                                               |    0.000 |
|  3 | system user |                 | NULL | Daemon  | NULL | InnoDB purge worker      | NULL                                               |    0.000 |
|  4 | system user |                 | NULL | Daemon  | NULL | InnoDB purge worker      | NULL                                               |    0.000 |
|  5 | system user |                 | NULL | Daemon  | NULL | InnoDB shutdown handler  | NULL                                               |    0.000 |
|  8 | root        | localhost:50473 | phd  | Killed  |  402 | Sending data             
| select count(*) from signals where signal_num = 20 |    0.000 |
| 10 | root        | localhost:50477 | phd  | Query   |    0 | init                     
| show processlist                                   |    0.000 |
| 11 | root        | localhost:50489 | NULL | Query   |   48 | Filling schema table     | SHOW STATUS                                        |    0.000 
|
+----+-------------+-----------------+------+---------+------+--------------------------+----------------------------------------------------+----------+
8 rows in set (0.00 sec)

当我尝试刷新表时，它在没有CPU使用的情况下挂起（即看起来它没有做任何事情？） .

[编辑]根据评论，这是统计结果 .

MariaDB [(none)]> select distinct COMMENT from information_schema.statistics where TABLE_SCHEMA='phd' and table_schema='signals';
Empty set (0.00 sec)

知道我的数据库发生了什么事吗？