lock table read/write區別
阿新 • • 發佈：2019-01-09
mysql lock
lock table table_nmae read|write
unlock tables
[email protected]:32:27[q]>lock table t1 read ; [email protected]:39:14[q]>show processlist ; +----+------+-----------+--------------------+---------+------+----------+------------------+ | Id | User | Host | db | Command | Time | State | Info | +----+------+-----------+--------------------+---------+------+----------+------------------+ | 5 | root | localhost | q | Sleep | 4344 | | NULL | | 6 | root | localhost | q | Sleep | 4431 | | NULL | | 8 | root | localhost | information_schema | Sleep | 4558 | | NULL | | 10 | root | localhost | q | Query | 0 | starting | show processlist | | 11 | root | localhost | q | Sleep | 27 | | NULL | +----+------+-----------+--------------------+---------+------+----------+------------------+
當前會話操作只能對t1表read ,不能write：
[email protected]:36:47[q]>select * from t1 ;
+------+------+
| name | age |
+------+------+
| a6 | 6 |
| a5 | 5 |
| a6 | 6 |
| a | 1 |
+------+------+
[email protected]
當前會話對其它表不能read,write
[email protected]:37:17[q]>select * from node ;
ERROR 1100 (HY000): Table 'node' was not locked with LOCK TABLES其它會話對錶t1的dml操作都會metalock鎖等待，對其它表沒影響：
其它會話操作：
[email protected]:39:19[q]>insert into t1 select *from ; 卡住 metadata lock 等待。
[email protected]:39:20[q]>show processlist ;
+----+------+-----------+--------------------+---------+------+---------------------------------+--------------------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------+--------------------+---------+------+---------------------------------+--------------------------------+
| 5 | root | localhost | q | Sleep | 4397 | | NULL |
| 6 | root | localhost | q | Sleep | 4484 | | NULL |
| 8 | root | localhost | information_schema | Sleep | 4611 | | NULL |
| 10 | root | localhost | q | Query | 0 | starting | show processlist |
| 11 | root | localhost | q | Query | 32 | Waiting for table metadata lock | insert into t1 select *from t1 |
+----+------+-----------+--------------------+---------+------+---------------------------------+--------------------------------+解鎖
[email protected]:40:13[q]>unlock table ;
Query OK, 0 rows affected (0.00 sec)
[email protected]:39:19[q]>insert into t1 select *from t1 ;
Query OK, 3 rows affected (1 min 36.86 sec)
Records: 3 Duplicates: 0 Warnings: 0
[email protected]:41:18[q]>show processlist ;
+----+------+-----------+--------------------+---------+------+----------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------+--------------------+---------+------+----------+------------------+
| 5 | root | localhost | q | Sleep | 4485 | | NULL |
| 6 | root | localhost | q | Sleep | 4572 | | NULL |
| 8 | root | localhost | information_schema | Sleep | 4699 | | NULL |
| 10 | root | localhost | q | Query | 0 | starting | show processlist |
| 11 | root | localhost | q | Sleep | 120 | | NULL |
+----+------+-----------+--------------------+---------+------+----------+------------------+
LOCK TABLE t1 WRITE
write帶read許可權
當前會話可以對指定表t1進行read ,write ；其它表不行。
[email protected]:25:59[q]>lock table t1 write ;
Query OK, 0 rows affected (5.03 sec)
[email protected]:29:25[q]>show processlist ;
+----+------+-----------+------+---------+------+----------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------+------+---------+------+----------+------------------+
| 18 | root | localhost | q | Sleep | 7 | | NULL |
| 22 | root | localhost | q | Query | 0 | starting | show processlist |
+----+------+-----------+------+---------+------+----------+------------------+
[email protected]:29:32[q]>select * from t1 ;
+------+------+
| name | age |
+------+------+
| a6 | 6 |
| a5 | 5 |
| a6 | 6 |
+------+------+[email protected]:29:36[q]>insert into t1 select * from t1 ;
ERROR 1100 (HY000): Table 't1' was not locked with LOCK TABLES
[email protected]:29:45[q]>insert into t1 select 'a',1 ;
Query OK, 1 row affected (0.00 sec)
Records: 1 Duplicates: 0 Warnings: 0
[email protected]:30:00[q]>select * from node limit 1 ;
ERROR 1100 (HY000): Table 'node' was not locked with LOCK TABLES其它會話不能對錶t1當前read,write ,其它可以正常操作
[email protected]:29:25[q]>select * from t1 ; -- 直接卡住
[email protected]:31:05[q]>select * from node limit 1 ; -- 其它表正常
+----+------+-----------+
| id | name | parent_id |
+----+------+-----------+
| 11 | 3 | 0 |
+----+------+-----------+
鎖的區別
lock tables/ flush table read lock
flush table read lock: 全域性讀鎖 ，解鎖：unlock tables
lock table table_name read/write :指定表鎖，解鎖:unlock table table_name /unlock tables table_names 每次只能持一個鎖
lock tables table read :沒有會話能DML read-locked 表
lock tables table_name write :除了持有鎖會話，沒有會話能訪問write-locked表