mysql锁
查询表级锁争用情况
MySQL表级锁的锁模式
请求锁模式
是否兼容
当前锁模式
|
None | 读锁 | 写锁 |
读锁 | 是 | 是 | 否 |
写锁 | 是 | 否 | 否 |
session_1 | session_2 |
获得表film_text的WRITE锁定
mysql> lock table film_text write;
Query OK, 0 rows affected (0.00 sec)
|
|
当前session对锁定表的查询、更新、插入操作都可以执行:
mysql> select film_id,title from film_text where film_id = 1001;
+---------+-------------+
| film_id | title |
+---------+-------------+
| 1001 | Update Test |
+---------+-------------+
1 row in set (0.00 sec)
mysql> insert into film_text (film_id,title) values(1003,'Test');
Query OK, 1 row affected (0.00 sec)
mysql> update film_text set title = 'Test' where film_id = 1001;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
|
其他session对锁定表的查询被阻塞,需要等待锁被释放:
mysql> select film_id,title from film_text where film_id = 1001;
等待
|
释放锁:
mysql> unlock tables;
Query OK, 0 rows affected (0.00 sec)
|
等待 |
Session2获得锁,查询返回:
mysql> select film_id,title from film_text where film_id = 1001;
+---------+-------+
| film_id | title |
+---------+-------+
| 1001 | Test |
+---------+-------+
1 row in set (57.59 sec)
|
如何加表锁
session_1 | session_2 |
获得表film_text的READ锁定
mysql> lock table film_text read;
Query OK, 0 rows affected (0.00 sec)
|
|
当前session可以查询该表记录
mysql> select film_id,title from film_text where film_id = 1001;
+---------+------------------+
| film_id | title |
+---------+------------------+
| 1001 | ACADEMY DINOSAUR |
+---------+------------------+
1 row in set (0.00 sec)
|
其他session也可以查询该表的记录
mysql> select film_id,title from film_text where film_id = 1001;
+---------+------------------+
| film_id | title |
+---------+------------------+
| 1001 | ACADEMY DINOSAUR |
+---------+------------------+
1 row in set (0.00 sec)
|
当前session不能查询没有锁定的表
mysql> select film_id,title from film where film_id = 1001;
ERROR 1100 (HY000): Table 'film' was not locked with LOCK TABLES
|
其他session可以查询或者更新未锁定的表
mysql> select film_id,title from film where film_id = 1001;
+---------+---------------+
| film_id | title |
+---------+---------------+
| 1001 | update record |
+---------+---------------+
1 row in set (0.00 sec)
mysql> update film set title = 'Test' where film_id = 1001;
Query OK, 1 row affected (0.04 sec)
Rows matched: 1 Changed: 1 Warnings: 0
|
当前session中插入或者更新锁定的表都会提示错误:
mysql> insert into film_text (film_id,title) values(1002,'Test');
ERROR 1099 (HY000): Table 'film_text' was locked with a READ lock and can't be updated
mysql> update film_text set title = 'Test' where film_id = 1001;
ERROR 1099 (HY000): Table 'film_text' was locked with a READ lock and can't be updated
|
其他session更新锁定表会等待获得锁:
mysql> update film_text set title = 'Test' where film_id = 1001;
等待
|
释放锁
mysql> unlock tables;
Query OK, 0 rows affected (0.00 sec)
|
等待 |
Session获得锁,更新操作完成:
mysql> update film_text set title = 'Test' where film_id = 1001;
Query OK, 1 row affected (1 min 0.71 sec)
Rows matched: 1 Changed: 1 Warnings: 0
|
并发插入(Concurrent Inserts)
session_1 | session_2 |
获得表film_text的READ LOCAL锁定
mysql> lock table film_text read local;
Query OK, 0 rows affected (0.00 sec)
|
|
当前session不能对锁定表进行更新或者插入操作:
mysql> insert into film_text (film_id,title) values(1002,'Test');
ERROR 1099 (HY000): Table 'film_text' was locked with a READ lock and can't be updated
mysql> update film_text set title = 'Test' where film_id = 1001;
ERROR 1099 (HY000): Table 'film_text' was locked with a READ lock and can't be updated
|
其他session可以进行插入操作,但是更新会等待:
mysql> insert into film_text (film_id,title) values(1002,'Test');
Query OK, 1 row affected (0.00 sec)
mysql> update film_text set title = 'Update Test' where film_id = 1001;
等待
|
当前session不能访问其他session插入的记录:
mysql> select film_id,title from film_text where film_id = 1002;
Empty set (0.00 sec)
|
|
释放锁:
mysql> unlock tables;
Query OK, 0 rows affected (0.00 sec)
|
等待 |
当前session解锁后可以获得其他session插入的记录:
mysql> select film_id,title from film_text where film_id = 1002;
+---------+-------+
| film_id | title |
+---------+-------+
| 1002 | Test |
+---------+-------+
1 row in set (0.00 sec)
|
Session2获得锁,更新操作完成:
mysql> update film_text set title = 'Update Test' where film_id = 1001;
Query OK, 1 row affected (1 min 17.75 sec)
Rows matched: 1 Changed: 1 Warnings: 0
|
MyISAM的锁调度
背景知识
1.事务(Transaction)及其ACID属性
2.并发事务处理带来的问题
3.事务隔离级别
读数据一致性及允许的并发副作用
隔离级别
|
读数据一致性 | 脏读 | 不可重复读 | 幻读 |
未提交读(Read uncommitted)
|
最低级别,只能保证不读取物理上损坏的数据 | 是 | 是 | 是 |
已提交度(Read committed)
|
语句级 | 否 | 是 | 是 |
可重复读(Repeatable read)
|
事务级 | 否 | 否 | 是 |
可序列化(Serializable)
|
最高级别,事务级 | 否 | 否 | 否 |
获取InnoDB行锁争用情况
InnoDB的行锁模式及加锁方法
请求锁模式
是否兼容
当前锁模式
|
X | IX | S | IS |
X | 冲突 | 冲突 | 冲突 | 冲突 |
IX | 冲突 | 兼容 | 冲突 | 兼容 |
S | 冲突 | 冲突 | 兼容 | 兼容 |
IS | 冲突 | 兼容 | 兼容 | 兼容 |
session_1 | session_2 |
mysql> set autocommit = 0;
Query OK, 0 rows affected (0.00 sec)
mysql> select actor_id,first_name,last_name from actor where actor_id = 178;
+----------+------------+-----------+
| actor_id | first_name | last_name |
+----------+------------+-----------+
| 178 | LISA | MONROE |
+----------+------------+-----------+
1 row in set (0.00 sec)
|
mysql> set autocommit = 0;
Query OK, 0 rows affected (0.00 sec)
mysql> select actor_id,first_name,last_name from actor where actor_id = 178;
+----------+------------+-----------+
| actor_id | first_name | last_name |
+----------+------------+-----------+
| 178 | LISA | MONROE |
+----------+------------+-----------+
1 row in set (0.00 sec)
|
当前session对actor_id=178的记录加share mode 的共享锁:
mysql> select actor_id,first_name,last_name from actor where actor_id = 178lock in share mode;
+----------+------------+-----------+
| actor_id | first_name | last_name |
+----------+------------+-----------+
| 178 | LISA | MONROE |
+----------+------------+-----------+
1 row in set (0.01 sec)
|
|
其他session仍然可以查询记录,并也可以对该记录加share mode的共享锁:
mysql> select actor_id,first_name,last_name from actor where actor_id = 178lock in share mode;
+----------+------------+-----------+
| actor_id | first_name | last_name |
+----------+------------+-----------+
| 178 | LISA | MONROE |
+----------+------------+-----------+
1 row in set (0.01 sec)
|
|
当前session对锁定的记录进行更新操作,等待锁:
mysql> update actor set last_name = 'MONROE T' where actor_id = 178;
等待
|
|
其他session也对该记录进行更新操作,则会导致死锁退出:
mysql> update actor set last_name = 'MONROE T' where actor_id = 178;
ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction
|
|
获得锁后,可以成功更新:
mysql> update actor set last_name = 'MONROE T' where actor_id = 178;
Query OK, 1 row affected (17.67 sec)
Rows matched: 1 Changed: 1 Warnings: 0
|
session_1 | session_2 |
mysql> set autocommit = 0;
Query OK, 0 rows affected (0.00 sec)
mysql> select actor_id,first_name,last_name from actor where actor_id = 178;
+----------+------------+-----------+
| actor_id | first_name | last_name |
+----------+------------+-----------+
| 178 | LISA | MONROE |
+----------+------------+-----------+
1 row in set (0.00 sec)
|
mysql> set autocommit = 0;
Query OK, 0 rows affected (0.00 sec)
mysql> select actor_id,first_name,last_name from actor where actor_id = 178;
+----------+------------+-----------+
| actor_id | first_name | last_name |
+----------+------------+-----------+
| 178 | LISA | MONROE |
+----------+------------+-----------+
1 row in set (0.00 sec)
|
当前session对actor_id=178的记录加for update的排它锁:
mysql> select actor_id,first_name,last_name from actor where actor_id = 178 for update;
+----------+------------+-----------+
| actor_id | first_name | last_name |
+----------+------------+-----------+
| 178 | LISA | MONROE |
+----------+------------+-----------+
1 row in set (0.00 sec)
|
|
其他session可以查询该记录,但是不能对该记录加共享锁,会等待获得锁:
mysql> select actor_id,first_name,last_name from actor where actor_id = 178;
+----------+------------+-----------+
| actor_id | first_name | last_name |
+----------+------------+-----------+
| 178 | LISA | MONROE |
+----------+------------+-----------+
1 row in set (0.00 sec)
mysql> select actor_id,first_name,last_name from actor where actor_id = 178 for update;
等待
|
|
当前session可以对锁定的记录进行更新操作,更新后释放锁:
mysql> update actor set last_name = 'MONROE T' where actor_id = 178;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> commit;
Query OK, 0 rows affected (0.01 sec)
|
|
其他session获得锁,得到其他session提交的记录:
mysql> select actor_id,first_name,last_name from actor where actor_id = 178 for update;
+----------+------------+-----------+
| actor_id | first_name | last_name |
+----------+------------+-----------+
| 178 | LISA | MONROE T |
+----------+------------+-----------+
1 row in set (9.59 sec)
|
InnoDB行锁实现方式
session_1 | session_2 |
mysql> set autocommit=0;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from tab_no_index where id = 1 ;
+------+------+
| id | name |
+------+------+
| 1 | 1 |
+------+------+
1 row in set (0.00 sec)
|
mysql> set autocommit=0;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from tab_no_index where id = 2 ;
+------+------+
| id | name |
+------+------+
| 2 | 2 |
+------+------+
1 row in set (0.00 sec)
|
mysql> select * from tab_no_index where id = 1 for update;
+------+------+
| id | name |
+------+------+
| 1 | 1 |
+------+------+
1 row in set (0.00 sec)
|
|
mysql> select * from tab_no_index where id = 2 for update;
等待
|
session_1 | session_2 |
mysql> set autocommit=0;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from tab_with_index where id = 1 ;
+------+------+
| id | name |
+------+------+
| 1 | 1 |
+------+------+
1 row in set (0.00 sec)
|
mysql> set autocommit=0;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from tab_with_index where id = 2 ;
+------+------+
| id | name |
+------+------+
| 2 | 2 |
+------+------+
1 row in set (0.00 sec)
|
mysql> select * from tab_with_index where id = 1 for update;
+------+------+
| id | name |
+------+------+
| 1 | 1 |
+------+------+
1 row in set (0.00 sec)
|
|
mysql> select * from tab_with_index where id = 2 for update;
+------+------+
| id | name |
+------+------+
| 2 | 2 |
+------+------+
1 row in set (0.00 sec)
|
session_1 | session_2 |
mysql> set autocommit=0;
Query OK, 0 rows affected (0.00 sec)
|
mysql> set autocommit=0;
Query OK, 0 rows affected (0.00 sec)
|
mysql> select * from tab_with_index where id = 1 and name = '1' for update;
+------+------+
| id | name |
+------+------+
| 1 | 1 |
+------+------+
1 row in set (0.00 sec)
|
|
虽然session_2访问的是和session_1不同的记录,但是因为使用了相同的索引,所以需要等待锁:
mysql> select * from tab_with_index where id = 1 and name = '4' for update;
等待
|
session_1 | session_2 |
mysql> set autocommit=0;
Query OK, 0 rows affected (0.00 sec)
|
mysql> set autocommit=0;
Query OK, 0 rows affected (0.00 sec)
|
mysql> select * from tab_with_index where id = 1 for update;
+------+------+
| id | name |
+------+------+
| 1 | 1 |
| 1 | 4 |
+------+------+
2 rows in set (0.00 sec)
|
|
Session_2使用name的索引访问记录,因为记录没有被索引,所以可以获得锁:
mysql> select * from tab_with_index where name = '2' for update;
+------+------+
| id | name |
+------+------+
| 2 | 2 |
+------+------+
1 row in set (0.00 sec)
|
|
由于访问的记录已经被session_1锁定,所以等待获得锁。:
mysql> select * from tab_with_index where name = '4' for update;
|
间隙锁(Next-Key锁)
session_1 | session_2 |
mysql> select @@tx_isolation;
+-----------------+
| @@tx_isolation |
+-----------------+
| REPEATABLE-READ |
+-----------------+
1 row in set (0.00 sec)
mysql> set autocommit = 0;
Query OK, 0 rows affected (0.00 sec)
|
mysql> select @@tx_isolation;
+-----------------+
| @@tx_isolation |
+-----------------+
| REPEATABLE-READ |
+-----------------+
1 row in set (0.00 sec)
mysql> set autocommit = 0;
Query OK, 0 rows affected (0.00 sec)
|
当前session对不存在的记录加for update的锁:
mysql> select * from emp where empid = 102 for update;
Empty set (0.00 sec)
|
|
这时,如果其他session插入empid为102的记录(注意:这条记录并不存在),也会出现锁等待:
mysql>insert into emp(empid,...) values(102,...);
阻塞等待
|
|
Session_1 执行rollback:
mysql> rollback;
Query OK, 0 rows affected (13.04 sec)
|
|
由于其他session_1回退后释放了Next-Key锁,当前session可以获得锁并成功插入记录:
mysql>insert into emp(empid,...) values(102,...);
Query OK, 1 row affected (13.35 sec)
|
恢复和复制的需要,对InnoDB锁机制的影响
session_1 | session_2 |
mysql> set autocommit = 0;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from target_tab;
Empty set (0.00 sec)
mysql> select * from source_tab where name = '1';
+----+------+----+
| d1 | name | d2 |
+----+------+----+
| 4 | 1 | 1 |
| 5 | 1 | 1 |
| 6 | 1 | 1 |
| 7 | 1 | 1 |
| 8 | 1 | 1 |
+----+------+----+
5 rows in set (0.00 sec)
|
mysql> set autocommit = 0;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from target_tab;
Empty set (0.00 sec)
mysql> select * from source_tab where name = '1';
+----+------+----+
| d1 | name | d2 |
+----+------+----+
| 4 | 1 | 1 |
| 5 | 1 | 1 |
| 6 | 1 | 1 |
| 7 | 1 | 1 |
| 8 | 1 | 1 |
+----+------+----+
5 rows in set (0.00 sec)
|
mysql> insert into target_tab select d1,name from source_tab where name = '1';
Query OK, 5 rows affected (0.00 sec)
Records: 5 Duplicates: 0 Warnings: 0
|
|
mysql> update source_tab set name = '1' where name = '8';
等待
|
|
commit; | |
返回结果
commit;
|
session_1 | session_2 |
mysql> set autocommit = 0;
Query OK, 0 rows affected (0.00 sec)
mysql>set innodb_locks_unsafe_for_binlog='on'
Query OK, 0 rows affected (0.00 sec)
mysql> select * from target_tab;
Empty set (0.00 sec)
mysql> select * from source_tab where name = '1';
+----+------+----+
| d1 | name | d2 |
+----+------+----+
| 4 | 1 | 1 |
| 5 | 1 | 1 |
| 6 | 1 | 1 |
| 7 | 1 | 1 |
| 8 | 1 | 1 |
+----+------+----+
5 rows in set (0.00 sec)
|
mysql> set autocommit = 0;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from target_tab;
Empty set (0.00 sec)
mysql> select * from source_tab where name = '1';
+----+------+----+
| d1 | name | d2 |
+----+------+----+
| 4 | 1 | 1 |
| 5 | 1 | 1 |
| 6 | 1 | 1 |
| 7 | 1 | 1 |
| 8 | 1 | 1 |
+----+------+----+
5 rows in set (0.00 sec)
|
mysql> insert into target_tab select d1,name from source_tab where name = '1';
Query OK, 5 rows affected (0.00 sec)
Records: 5 Duplicates: 0 Warnings: 0
|
|
session_1未提交,可以对session_1的select的记录进行更新操作。
mysql> update source_tab set name = '8' where name = '1';
Query OK, 5 rows affected (0.00 sec)
Rows matched: 5 Changed: 5 Warnings: 0
mysql> select * from source_tab where name = '8';
+----+------+----+
| d1 | name | d2 |
+----+------+----+
| 4 | 8 | 1 |
| 5 | 8 | 1 |
| 6 | 8 | 1 |
| 7 | 8 | 1 |
| 8 | 8 | 1 |
+----+------+----+
5 rows in set (0.00 sec)
|
|
更新操作先提交
mysql> commit;
Query OK, 0 rows affected (0.05 sec)
|
|
插入操作后提交
mysql> commit;
Query OK, 0 rows affected (0.07 sec)
|
|
此时查看数据,target_tab中可以插入source_tab更新前的结果,这符合应用逻辑:
mysql> select * from source_tab where name = '8';
+----+------+----+
| d1 | name | d2 |
+----+------+----+
| 4 | 8 | 1 |
| 5 | 8 | 1 |
| 6 | 8 | 1 |
| 7 | 8 | 1 |
| 8 | 8 | 1 |
+----+------+----+
5 rows in set (0.00 sec)
mysql> select * from target_tab;
+------+------+
| id | name |
+------+------+
| 4 | 1.00 |
| 5 | 1.00 |
| 6 | 1.00 |
| 7 | 1.00 |
| 8 | 1.00 |
+------+------+
5 rows in set (0.00 sec)
|
mysql> select * from tt1 where name = '1';
Empty set (0.00 sec)
mysql> select * from source_tab where name = '8';
+----+------+----+
| d1 | name | d2 |
+----+------+----+
| 4 | 8 | 1 |
| 5 | 8 | 1 |
| 6 | 8 | 1 |
| 7 | 8 | 1 |
| 8 | 8 | 1 |
+----+------+----+
5 rows in set (0.00 sec)
mysql> select * from target_tab;
+------+------+
| id | name |
+------+------+
| 4 | 1.00 |
| 5 | 1.00 |
| 6 | 1.00 |
| 7 | 1.00 |
| 8 | 1.00 |
+------+------+
5 rows in set (0.00 sec)
|
InnoDB在不同隔离级别下的一致性读及锁的差异
隔离级别
一致性读和锁
SQL
|
Read Uncommited | Read Commited | Repeatable Read | Serializable | |
SQL | 条件 | ||||
select | 相等 | None locks | Consisten read/None lock | Consisten read/None lock | Share locks |
范围 | None locks | Consisten read/None lock | Consisten read/None lock | Share Next-Key | |
update | 相等 | exclusive locks | exclusive locks | exclusive locks | Exclusive locks |
范围 | exclusive next-key | exclusive next-key | exclusive next-key | exclusive next-key | |
Insert | N/A | exclusive locks | exclusive locks | exclusive locks | exclusive locks |
replace | 无键冲突 | exclusive locks | exclusive locks | exclusive locks | exclusive locks |
键冲突 | exclusive next-key | exclusive next-key | exclusive next-key | exclusive next-key | |
delete | 相等 | exclusive locks | exclusive locks | exclusive locks | exclusive locks |
范围 | exclusive next-key | exclusive next-key | exclusive next-key | exclusive next-key | |
Select ... from ... Lock in share mode | 相等 | Share locks | Share locks | Share locks | Share locks |
范围 | Share locks | Share locks | Share Next-Key | Share Next-Key | |
Select * from ... For update | 相等 | exclusive locks | exclusive locks | exclusive locks | exclusive locks |
范围 | exclusive locks | Share locks | exclusive next-key | exclusive next-key | |
Insert into ... Select ...
(指源表锁)
|
innodb_locks_unsafe_for_binlog=off | Share Next-Key | Share Next-Key | Share Next-Key | Share Next-Key |
innodb_locks_unsafe_for_binlog=on | None locks | Consisten read/None lock | Consisten read/None lock | Share Next-Key | |
create table ... Select ...
(指源表锁)
|
innodb_locks_unsafe_for_binlog=off | Share Next-Key | Share Next-Key | Share Next-Key | Share Next-Key |
innodb_locks_unsafe_for_binlog=on | None locks | Consisten read/None lock | Consisten read/None lock | Share Next-Key |
什么时候使用表锁
关于死锁
session_1 | session_2 |
mysql> set autocommit = 0;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from table_1 where where id=1 for update;
...
做一些其他处理...
|
mysql> set autocommit = 0;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from table_2 where id=1 for update;
...
|
select * from table_2 where id =1 for update;
因session_2已取得排他锁,等待
|
做一些其他处理... |
mysql> select * from table_1 where where id=1 for update;
死锁
|
session_1 | session_2 |
mysql> set autocommit=0;
Query OK, 0 rows affected (0.00 sec)
|
mysql> set autocommit=0;
Query OK, 0 rows affected (0.00 sec)
|
mysql> select first_name,last_name from actor where actor_id = 1 for update;
+------------+-----------+
| first_name | last_name |
+------------+-----------+
| PENELOPE | GUINESS |
+------------+-----------+
1 row in set (0.00 sec)
|
|
mysql> insert into country (country_id,country) values(110,'Test');
Query OK, 1 row affected (0.00 sec)
|
|
mysql> insert into country (country_id,country) values(110,'Test');
等待
|
|
mysql> select first_name,last_name from actor where actor_id = 1 for update;
+------------+-----------+
| first_name | last_name |
+------------+-----------+
| PENELOPE | GUINESS |
+------------+-----------+
1 row in set (0.00 sec)
|
|
mysql> insert into country (country_id,country) values(110,'Test');
ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction
|
session_1 | session_2 |
mysql> set autocommit=0;
Query OK, 0 rows affected (0.00 sec)
|
mysql> set autocommit=0;
Query OK, 0 rows affected (0.00 sec)
|
mysql> select first_name,last_name from actor where actor_id = 1 for update;
+------------+-----------+
| first_name | last_name |
+------------+-----------+
| PENELOPE | GUINESS |
+------------+-----------+
1 row in set (0.00 sec)
|
|
mysql> select first_name,last_name from actor where actor_id = 3 for update;
+------------+-----------+
| first_name | last_name |
+------------+-----------+
| ED | CHASE |
+------------+-----------+
1 row in set (0.00 sec)
|
|
mysql> select first_name,last_name from actor where actor_id = 3 for update;
等待
|
|
mysql> select first_name,last_name from actor where actor_id = 1 for update;
ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction
|
|
mysql> select first_name,last_name from actor where actor_id = 3 for update;
+------------+-----------+
| first_name | last_name |
+------------+-----------+
| ED | CHASE |
+------------+-----------+
1 row in set (4.71 sec)
|
session_1 | session_2 |
mysql> select @@tx_isolation;
+-----------------+
| @@tx_isolation |
+-----------------+
| REPEATABLE-READ |
+-----------------+
1 row in set (0.00 sec)
mysql> set autocommit = 0;
Query OK, 0 rows affected (0.00 sec)
|
mysql> select @@tx_isolation;
+-----------------+
| @@tx_isolation |
+-----------------+
| REPEATABLE-READ |
+-----------------+
1 row in set (0.00 sec)
mysql> set autocommit = 0;
Query OK, 0 rows affected (0.00 sec)
|
当前session对不存在的记录加for update的锁:
mysql> select actor_id,first_name,last_name from actor where actor_id = 201 for update;
Empty set (0.00 sec)
|
|
其他session也可以对不存在的记录加for update的锁:
mysql> select actor_id,first_name,last_name from actor where actor_id = 201 for update;
Empty set (0.00 sec)
|
|
因为其他session也对该记录加了锁,所以当前的插入会等待:
mysql> insert into actor (actor_id , first_name , last_name) values(201,'Lisa','Tom');
等待
|
|
因为其他session已经对记录进行了更新,这时候再插入记录就会提示死锁并退出:
mysql> insert into actor (actor_id, first_name , last_name) values(201,'Lisa','Tom');
ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction
|
|
由于其他session已经退出,当前session可以获得锁并成功插入记录:
mysql> insert into actor (actor_id , first_name , last_name) values(201,'Lisa','Tom');
Query OK, 1 row affected (13.35 sec)
|
session_1 | session_2 | session_3 |
mysql> select @@tx_isolation;
+----------------+
| @@tx_isolation |
+----------------+
| READ-COMMITTED |
+----------------+
1 row in set (0.00 sec)
mysql> set autocommit=0;
Query OK, 0 rows affected (0.01 sec)
|
mysql> select @@tx_isolation;
+----------------+
| @@tx_isolation |
+----------------+
| READ-COMMITTED |
+----------------+
1 row in set (0.00 sec)
mysql> set autocommit=0;
Query OK, 0 rows affected (0.01 sec)
|
mysql> select @@tx_isolation;
+----------------+
| @@tx_isolation |
+----------------+
| READ-COMMITTED |
+----------------+
1 row in set (0.00 sec)
mysql> set autocommit=0;
Query OK, 0 rows affected (0.01 sec)
|
Session_1获得for update的共享锁:
mysql> select actor_id, first_name,last_name from actor where actor_id = 201 for update;
Empty set (0.00 sec)
|
由于记录不存在,session_2也可以获得for update的共享锁:
mysql> select actor_id, first_name,last_name from actor where actor_id = 201 for update;
Empty set (0.00 sec)
|
|
Session_1可以成功插入记录:
mysql> insert into actor (actor_id,first_name,last_name) values(201,'Lisa','Tom');
Query OK, 1 row affected (0.00 sec)
|
||
Session_2插入申请等待获得锁:
mysql> insert into actor (actor_id,first_name,last_name) values(201,'Lisa','Tom');
等待
|
||
Session_1成功提交:
mysql> commit;
Query OK, 0 rows affected (0.04 sec)
|
||
Session_2获得锁,发现插入记录主键重,这个时候抛出了异常,但是并没有释放共享锁:
mysql> insert into actor (actor_id,first_name,last_name) values(201,'Lisa','Tom');
ERROR 1062 (23000): Duplicate entry '201' for key 'PRIMARY'
|
||
Session_3申请获得共享锁,因为session_2已经锁定该记录,所以session_3需要等待:
mysql> select actor_id, first_name,last_name from actor where actor_id = 201 for update;
等待
|
||
这个时候,如果session_2直接对记录进行更新操作,则会抛出死锁的异常:
mysql> update actor set last_name='Lan' where actor_id = 201;
ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction
|
||
Session_2释放锁后,session_3获得锁:
mysql> select first_name, last_name from actor where actor_id = 201 for update;
+------------+-----------+
| first_name | last_name |
+------------+-----------+
| Lisa | Tom |
+------------+-----------+
1 row in set (31.12 sec)
|
mysql锁的更多相关文章
- Mysql锁初步
存储引擎 要了解mysql的锁,就要先从存储引擎说起. 常用存储引擎列表如下图所示: 最常使用的两种存储引擎: Myisam是Mysql的默认存储引擎.当create创建新表时,未指定新表的存储引擎时 ...
- mysql锁表机制及相关优化
(该文章为方便自己查阅,也希望对大家有所帮助,转载于互联网) 1. 锁机制 当前MySQL支持 ISAM, MyISAM, MEMORY (HEAP) 类型表的表级锁,BDB 表支持页级锁,InnoD ...
- MySQL锁系列3 MDL锁
http://www.cnblogs.com/xpchild/p/3790139.html MySQL为了保护数据字典元数据,使用了metadata lock,即MDL锁,保证在并发的情况下,结构 ...
- 01 MySQL锁概述
锁是计算机协调多个进程或线程并发访问某一资源的机制.在数据库中,除传统的计算资源(如CPU.RAM.I/O 等)的争用以外,数据也是一种供许多用户共享的资源.如何保证数据并发访问的一致性.有效性是所有 ...
- Mysql锁机制介绍
Mysql锁机制介绍 一.概况MySQL的锁机制比较简单,其最显著的特点是不同的存储引擎支持不同的锁机制.比如,MyISAM和MEMORY存储引擎采用的是表级锁(table-level locking ...
- MySQL锁等待分析【2】
MySQL锁等待分析[1]中对锁等待的分析是一步一步来的.虽然最后是分析出来了,可是用时是比较长的:理清各个表之间的关系后,得到如下SQL语句,方便以后使用 select block_trx.trx_ ...
- MySQL锁与MVCC
--MySQL锁与MVCC --------------------2014/06/29 myisam表锁比较简单,这里主要讨论一下innodb的锁相关问题. innodb相比oracle锁机制简单许 ...
- MySQL锁总结
本文同时发表在https://github.com/zhangyachen/zhangyachen.github.io/issues/78 MySQL 锁基础 参考了何登成老师文章的结构MySQL 加 ...
- Mysql锁机制--并发事务带来的更新丢失问题
Mysql 系列文章主页 =============== 刚开始学习 Mysql 锁的时候,觉得 Mysql 使用的是行锁,再加上其默认的可重复读的隔离级别,那就应该能够自动解决并发事务更新的问题.可 ...
随机推荐
- 无法将 匿名方法 转换为类型“System.Delegate”,因为它不是委托类型:解决方法
http://blog.csdn.net/xiaochongchong1248/archive/2009/11/20/4841193.aspx?1271573283 编程环境要求:VS2008/FX2 ...
- gettter,delatter,settter
class Foo: x = 1 def __init__(self,y): self.y=y def __getattr__(self, item): print('自行--getatter') d ...
- 让apache后端显示真实客户端IP
公司是nginx做代理,后端的web服务用的是apache,然后我现在要分析日志,但是,我的apache日志上显示的是代理服务器的ip地址,不是客户的真实IP 所以这里我需要修改一下,让apache的 ...
- sql-将一个表中的数导入另一个表中
1.如果2张表的字段一致,并且希望插入全部数据 可以用这种方法: INSERT INTO 目标表 SELECT * FROM 来源表;例: insert into insertTest select ...
- 【BZOJ-4631】踩气球 线段树 + STL
4631: 踩气球 Time Limit: 10 Sec Memory Limit: 256 MBSubmit: 224 Solved: 114[Submit][Status][Discuss] ...
- 【bzoj2456】 mode
http://www.lydsy.com/JudgeOnline/problem.php?id=2456 (题目链接) 只看了一眼,直觉便告诉我这是水题.于是跟某码农打赌说10分钟做出来叫爸爸,结果输 ...
- HDU2222 Keywords Search
本文版权归ljh2000和博客园共有,欢迎转载,但须保留此声明,并给出原文链接,谢谢合作. 本文作者:ljh2000作者博客:http://www.cnblogs.com/ljh2000-jump/转 ...
- SQL Server表结构和数据导入到MySQL
借助的工具:Navicat for MySQL,链接:http://pan.baidu.com/s/1kVCw8IF 密码:g927 可以很明确的肯定,主键和自增列是没办法导入的,只能是表结构和数据. ...
- CruiseControl.NET与TFS结合的配置文件
配置如下: <cruisecontrol xmlns:cb="urn:ccnet.config.builder"> <project name="测试项 ...
- Android成长日记-使用ToggleButton实现灯的开关
案例演示 此案例实现思路:通过ToggleButton控件,ImageView控件实现 ---xml代码: <!-- textOn:true textOff:falase[s1] --> ...