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)