关于mysql MYISAM引擎的锁问题

CREATE TABLE `citymy` (

`city_id` smallint(5) unsigned NOT NULL DEFAULT '0',

`city` varchar(50) CHARACTER SET utf8 NOT NULL,

`country_id` smallint(5) unsigned NOT NULL,

`last_update` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP

) ENGINE=MyISAM DEFAULT CHARSET=latin1;

LOCK TABLES

tbl_name [[AS] alias] lock_type

[, tbl_name [[AS] alias] lock_type] ...

lock_type:

READ [LOCAL]

| [LOW_PRIORITY] WRITE

UNLOCK TABLES

LOCK TABLE citymy READ;

mysql> delete from citymy;

mysql>show processlist;

+----+------+--------------------+--------+---------+------+------------------------------+--------------------+

| Id | User | Host               | db     | Command | Time | State                        | Info               |

+----+------+--------------------+--------+---------+------+------------------------------+--------------------+

|  3 | root | localhost          | sakila | Query   | 1287 | Waiting for table level lock | delete from citymy |

|  8 | root | 10.180.2.152:51043 | sakila | Sleep   |  350 |                              | NULL               |

|  9 | root | 10.180.2.152:51044 | NULL   | Sleep   | 1701 |                              | NULL               |

| 40 | root | localhost          | NULL   | Query   |    0 | init                         | show processlist   |

+----+------+--------------------+--------+---------+------+------------------------------+--------------------+

4 rows in set (0.00 sec)

mysql> drop table citymy;

mysql> show processlist;

+----+------+--------------------+--------+---------+------+---------------------------------+--------------------+

| Id | User | Host               | db     | Command | Time | State                           | Info               |

+----+------+--------------------+--------+---------+------+---------------------------------+--------------------+

|  3 | root | localhost          | sakila | Query   | 1468 | Waiting for table level lock    | delete from citymy |

|  8 | root | 10.180.2.152:51043 | sakila | Sleep   |  531 |                                 | NULL               |

|  9 | root | 10.180.2.152:51044 | NULL   | Sleep   | 1882 |                                 | NULL               |

| 40 | root | localhost          | NULL   | Query   |    0 | init                            | show processlist   |

| 43 | root | localhost          | sakila | Query   |   94 | Waiting for table metadata lock | drop table citymy  |

| 44 | root | localhost          | sakila | Query   |   26 | Waiting for table metadata lock | drop table citymy  |

+----+------+--------------------+--------+---------+------+---------------------------------+--------------------+

6 rows in set (0.00 sec)