MySQL中锁详解(行锁、表锁、页锁、悲观锁、乐观锁等)
原文地址:http://blog.csdn.net/mysteryhaohao/article/details/51669741
锁,在现实生活中是为我们想要隐藏于外界所使用的一种工具。在计算机中,是协调多个进程或线程并发访问某一资源的一种机制。在数据库当中,除了传统的计算资源(CPU、RAM、I/O等等)的争用之外,数据也是一种供许多用户共享访问的资源。如何保证数据并发访问的一致性、有效性,是所有数据库必须解决的一个问题,锁的冲突也是影响数据库并发访问性能的一个重要因素。从这一角度来说,锁对于数据库而言就显得尤为重要。
MySQL锁
相对于其他的数据库而言,MySQL的锁机制比较简单,最显著的特点就是不同的存储引擎支持不同的锁机制。根据不同的存储引擎,MySQL中锁的特性可以大致归纳如下:
行锁 | 表锁 | 页锁 | |
MyISAM | √ | ||
BDB | √ | √ | |
InnoDB | √ | √ |
开销、加锁速度、死锁、粒度、并发性能
- 表锁:开销小,加锁快;不会出现死锁;锁定力度大,发生锁冲突概率高,并发度最低
- 行锁:开销大,加锁慢;会出现死锁;锁定粒度小,发生锁冲突的概率低,并发度高
- 页锁:开销和加锁速度介于表锁和行锁之间;会出现死锁;锁定粒度介于表锁和行锁之间,并发度一般
从上述的特点课件,很难笼统的说哪种锁最好,只能根据具体应用的特点来说哪种锁更加合适。仅仅从锁的角度来说的话:
表锁更适用于以查询为主,只有少量按索引条件更新数据的应用;行锁更适用于有大量按索引条件并发更新少量不同数据,同时又有并发查询的应用。(PS:由于BDB已经被InnoDB所取代,我们只讨论MyISAM表锁和InnoDB行锁的问题)
- mysql> show status like 'table%';
- +-----------------------+-------+
- | Variable_name | Value |
- +-----------------------+-------+
- | Table_locks_immediate | 2979 |
- | Table_locks_waited | 0 |
- +-----------------------+-------+
- 2 rows in set (0.00 sec))
mysql> show status like 'table%';
+-----------------------+-------+
| Variable_name | Value |
+-----------------------+-------+
| Table_locks_immediate | 2979 |
| Table_locks_waited | 0 |
+-----------------------+-------+
2 rows in set (0.00 sec))
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
- Select sum(total) from orders;
- Select sum(subtotal) from order_detail;
- 这时,如果不先给两个表加锁,就可能产生错误的结果,因为第一条语句执行过程中,order_detail表可能已经发生了改变。因此,正确的方法应该是:
- Lock tables orders read local, order_detail read local;
- Select sum(total) from orders;
- Select sum(subtotal) from order_detail;
- Unlock tables;
Select sum(total) from orders;
Select sum(subtotal) from order_detail;
这时,如果不先给两个表加锁,就可能产生错误的结果,因为第一条语句执行过程中,order_detail表可能已经发生了改变。因此,正确的方法应该是:
Lock tables orders read local, order_detail read local;
Select sum(total) from orders;
Select sum(subtotal) from order_detail;
Unlock tables;
- 上面的例子在LOCK TABLES时加了“local”选项,其作用就是在满足MyISAM表并发插入条件的情况下,允许其他用户在表尾并发插入记录,有关MyISAM表的并发插入问题,在后面的章节中还会进一步介绍。
- 在用LOCK TABLES给表显式加表锁时,必须同时取得所有涉及到表的锁,并且MySQL不支持锁升级。也就是说,在执行LOCK TABLES后,只能访问显式加锁的这些表,不能访问未加锁的表;同时,如果加的是读锁,那么只能执行查询操作,而不能执行更新操作。其实,在自动加锁的情况下也基本如此,MyISAM总是一次获得SQL语句所需要的全部锁。这也正是MyISAM表不会出现死锁(Deadlock Free)的原因。
在如下表所示的例子中,一个session使用LOCK TABLE命令给表film_text加了读锁,这个session可以查询锁定表中的记录,但更新或访问其他表都会提示错误;同时,另外一个session可以查询表中的记录,但更新就会出现锁等待。
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
|
注意,当使用LOCK TABLES时,不仅需要一次锁定用到的所有表,而且,同一个表在SQL语句中出现多少次,就要通过与SQL语句中相同的别名锁定多少次,否则也会出错!举例说明如下。
- (1)对actor表获得读锁:
- mysql> lock table actor read;
- Query OK, 0 rows affected (0.00 sec)
- (2)但是通过别名访问会提示错误:
- mysql> select a.first_name,a.last_name,b.first_name,b.last_name from actor a,actor b where a.first_name = b.first_name and a.first_name = 'Lisa' and a.last_name = 'Tom' and a.last_name <> b.last_name;
- ERROR 1100 (HY000): Table 'a' was not locked with LOCK TABLES
- (3)需要对别名分别锁定:
- mysql> lock table actor as a read,actor as b read;
- Query OK, 0 rows affected (0.00 sec)
- (4)按照别名的查询可以正确执行:
- mysql> select a.first_name,a.last_name,b.first_name,b.last_name from actor a,actor b where a.first_name = b.first_name and a.first_name = 'Lisa' and a.last_name = 'Tom' and a.last_name <> b.last_name;
- +------------+-----------+------------+-----------+
- | first_name | last_name | first_name | last_name |
- +------------+-----------+------------+-----------+
- | Lisa | Tom | LISA | MONROE |
- +------------+-----------+------------+-----------+
- 1 row in set (0.00 sec)
(1)对actor表获得读锁:
mysql> lock table actor read;
Query OK, 0 rows affected (0.00 sec)
(2)但是通过别名访问会提示错误:
mysql> select a.first_name,a.last_name,b.first_name,b.last_name from actor a,actor b where a.first_name = b.first_name and a.first_name = 'Lisa' and a.last_name = 'Tom' and a.last_name <> b.last_name;
ERROR 1100 (HY000): Table 'a' was not locked with LOCK TABLES
(3)需要对别名分别锁定:
mysql> lock table actor as a read,actor as b read;
Query OK, 0 rows affected (0.00 sec)
(4)按照别名的查询可以正确执行:
mysql> select a.first_name,a.last_name,b.first_name,b.last_name from actor a,actor b where a.first_name = b.first_name and a.first_name = 'Lisa' and a.last_name = 'Tom' and a.last_name <> b.last_name;
+------------+-----------+------------+-----------+
| first_name | last_name | first_name | last_name |
+------------+-----------+------------+-----------+
| Lisa | Tom | LISA | MONROE |
+------------+-----------+------------+-----------+
1 row in set (0.00 sec)
并发插入(Concurrent Inserts)
- 当concurrent_insert设置为0时,不允许并发插入。
- 当concurrent_insert设置为1时,如果MyISAM表中没有空洞(即表的中间没有被删除的行),MyISAM允许在一个进程读表的同时,另一个进程从表尾插入记录。这也是MySQL的默认设置。
- 当concurrent_insert设置为2时,无论MyISAM表中有没有空洞,都允许在表尾并发插入记录。
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
|
的调度行为。
- 通过指定启动参数low-priority-updates,使MyISAM引擎默认给予读请求以优先的权利。
- 通过执行命令SET LOW_PRIORITY_UPDATES=1,使该连接发出的更新请求优先级降低。
- 通过指定INSERT、UPDATE、DELETE语句的LOW_PRIORITY属性,降低该语句的优先级。
- 原子性(Atomicity):事务是一个原子操作单元,其对数据的修改,要么全都执行,要么全都不执行。
- 一致性(Consistent):在事务开始和完成时,数据都必须保持一致状态。这意味着所有相关的数据规则都必须应用于事务的修改,以保持数据的完整性;事务结束时,所有的内部数据结构(如B树索引或双向链表)也都必须是正确的。
- 隔离性(Isolation):数据库系统提供一定的隔离机制,保证事务在不受外部并发操作影响的“独立”环境执行。这意味着事务处理过程中的中间状态对外部是不可见的,反之亦然。
- 持久性(Durable):事务完成之后,它对于数据的修改是永久性的,即使出现系统故障也能够保持。
- 更新丢失(Lost Update):当两个或多个事务选择同一行,然后基于最初选定的值更新该行时,由于每个事务都不知道其他事务的存在,就会发生丢失更新问题--最后的更新覆盖了由其他事务所做的更新。例如,两个编辑人员制作了同一文档的电子副本。每个编辑人员独立地更改其副本,然后保存更改后的副本,这样就覆盖了原始文档。最后保存其更改副本的编辑人员覆盖另一个编辑人员所做的更改。如果在一个编辑人员完成并提交事务之前,另一个编辑人员不能访问同一文件,则可避免此问题。
- 脏读(Dirty Reads):一个事务正在对一条记录做修改,在这个事务完成并提交前,这条记录的数据就处于不一致状态;这时,另一个事务也来读取同一条记录,如果不加控制,第二个事务读取了这些“脏”数据,并据此做进一步的处理,就会产生未提交的数据依赖关系。这种现象被形象地叫做"脏读"。
- 不可重复读(Non-Repeatable Reads):一个事务在读取某些数据后的某个时间,再次读取以前读过的数据,却发现其读出的数据已经发生了改变、或某些记录已经被删除了!这种现象就叫做“不可重复读”。
- 幻读(Phantom Reads):一个事务按相同的查询条件重新读取以前检索过的数据,却发现其他事务插入了满足其查询条件的新数据,这种现象就称为“幻读”。
- 一种是在读取数据前,对其加锁,阻止其他事务对数据进行修改。
- 另一种是不用加任何锁,通过一定机制生成一个数据请求时间点的一致性数据快照(Snapshot),并用这个快照来提供一定级别(语句级或事务级)的一致性读取。从用户的角度来看,好像是数据库可以提供同一数据的多个版本,因此,这种技术叫做数据多版本并发控制(MultiVersion Concurrency Control,简称MVCC或MCC),也经常称为多版本数据库。
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 |
- mysql> show status like 'innodb_row_lock%';
- +-------------------------------+-------+
- | Variable_name | Value |
- +-------------------------------+-------+
- | InnoDB_row_lock_current_waits | 0 |
- | InnoDB_row_lock_time | 0 |
- | InnoDB_row_lock_time_avg | 0 |
- | InnoDB_row_lock_time_max | 0 |
- | InnoDB_row_lock_waits | 0 |
- +-------------------------------+-------+
- 5 rows in set (0.01 sec)
mysql> show status like 'innodb_row_lock%';
+-------------------------------+-------+
| Variable_name | Value |
+-------------------------------+-------+
| InnoDB_row_lock_current_waits | 0 |
| InnoDB_row_lock_time | 0 |
| InnoDB_row_lock_time_avg | 0 |
| InnoDB_row_lock_time_max | 0 |
| InnoDB_row_lock_waits | 0 |
+-------------------------------+-------+
5 rows in set (0.01 sec)
- 具体方法如下:
- mysql> CREATE TABLE innodb_monitor(a INT) ENGINE=INNODB;
- Query OK, 0 rows affected (0.14 sec)
- 然后就可以用下面的语句来进行查看:
- mysql> Show innodb status\G;
- *************************** 1. row ***************************
- Type: InnoDB
- Name:
- Status:
- …
- …
- ------------
- TRANSACTIONS
- ------------
- Trx id counter 0 117472192
- Purge done for trx's n:o < 0 117472190 undo n:o < 0 0
- History list length 17
- Total number of lock structs in row lock hash table 0
- LIST OF TRANSACTIONS FOR EACH SESSION:
- ---TRANSACTION 0 117472185, not started, process no 11052, OS thread id 1158191456
- MySQL thread id 200610, query id 291197 localhost root
- ---TRANSACTION 0 117472183, not started, process no 11052, OS thread id 1158723936
- MySQL thread id 199285, query id 291199 localhost root
- Show innodb status
- …
- 监视器可以通过发出下列语句来停止查看:
- mysql> DROP TABLE innodb_monitor;
- Query OK, 0 rows affected (0.05 sec)
具体方法如下:
mysql> CREATE TABLE innodb_monitor(a INT) ENGINE=INNODB;
Query OK, 0 rows affected (0.14 sec)
然后就可以用下面的语句来进行查看:
mysql> Show innodb status\G;
*************************** 1. row ***************************
Type: InnoDB
Name:
Status:
…
…
------------
TRANSACTIONS
------------
Trx id counter 0 117472192
Purge done for trx's n:o < 0 117472190 undo n:o < 0 0
History list length 17
Total number of lock structs in row lock hash table 0
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION 0 117472185, not started, process no 11052, OS thread id 1158191456
MySQL thread id 200610, query id 291197 localhost root
---TRANSACTION 0 117472183, not started, process no 11052, OS thread id 1158723936
MySQL thread id 199285, query id 291199 localhost root
Show innodb status
…
监视器可以通过发出下列语句来停止查看:
mysql> DROP TABLE innodb_monitor;
Query OK, 0 rows affected (0.05 sec)
- 共享锁(S):允许一个事务去读一行,阻止其他事务获得相同数据集的排他锁。
- 排他锁(X):允许获得排他锁的事务更新数据,阻止其他事务取得相同数据集的共享读锁和排他写锁。另外,为了允许行锁和表锁共存,实现多粒度锁机制,InnoDB还有两种内部使用的意向锁(Intention Locks),这两种意向锁都是表锁。
- 意向共享锁(IS):事务打算给数据行加行共享锁,事务在给一个数据行加共享锁前必须先取得该表的IS锁。
- 意向排他锁(IX):事务打算给数据行加行排他锁,事务在给一个数据行加排他锁前必须先取得该表的IX锁。
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 |
- 共享锁(S):SELECT * FROM table_name WHERE ... LOCK IN SHARE MODE。
- 排他锁(X):SELECT * FROM table_name WHERE ... FOR UPDATE。
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 = 178 lock 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 = 178 lock 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)
|
- mysql> create table tab_no_index(id int,name varchar(10)) engine=innodb;
- Query OK, 0 rows affected (0.15 sec)
- mysql> insert into tab_no_index values(1,'1'),(2,'2'),(3,'3'),(4,'4');
- Query OK, 4 rows affected (0.00 sec)
- Records: 4 Duplicates: 0 Warnings: 0
mysql> create table tab_no_index(id int,name varchar(10)) engine=innodb;
Query OK, 0 rows affected (0.15 sec)
mysql> insert into tab_no_index values(1,'1'),(2,'2'),(3,'3'),(4,'4');
Query OK, 4 rows affected (0.00 sec)
Records: 4 Duplicates: 0 Warnings: 0
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
|
- mysql> create table tab_with_index(id int,name varchar(10)) engine=innodb;
- Query OK, 0 rows affected (0.15 sec)
- mysql> alter table tab_with_index add index id(id);
- Query OK, 4 rows affected (0.24 sec)
- Records: 4 Duplicates: 0 Warnings: 0
mysql> create table tab_with_index(id int,name varchar(10)) engine=innodb;
Query OK, 0 rows affected (0.15 sec)
mysql> alter table tab_with_index add index id(id);
Query OK, 4 rows affected (0.24 sec)
Records: 4 Duplicates: 0 Warnings: 0
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)
|
- mysql> alter table tab_with_index drop index name;
- Query OK, 4 rows affected (0.22 sec)
- Records: 4 Duplicates: 0 Warnings: 0
- mysql> insert into tab_with_index values(1,'4');
- Query OK, 1 row affected (0.00 sec)
- mysql> select * from tab_with_index where id = 1;
- +------+------+
- | id | name |
- +------+------+
- | 1 | 1 |
- | 1 | 4 |
- +------+------+
- 2 rows in set (0.00 sec)
mysql> alter table tab_with_index drop index name;
Query OK, 4 rows affected (0.22 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> insert into tab_with_index values(1,'4');
Query OK, 1 row affected (0.00 sec)
mysql> select * from tab_with_index where id = 1;
+------+------+
| id | name |
+------+------+
| 1 | 1 |
| 1 | 4 |
+------+------+
2 rows 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
|
- mysql> alter table tab_with_index add index name(name);
- Query OK, 5 rows affected (0.23 sec)
- Records: 5 Duplicates: 0 Warnings: 0
mysql> alter table tab_with_index add index name(name);
Query OK, 5 rows affected (0.23 sec)
Records: 5 Duplicates: 0 Warnings: 0
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;
|
- mysql> alter table tab_no_index add index name(name);
- Query OK, 4 rows affected (8.06 sec)
- Records: 4 Duplicates: 0 Warnings: 0
- mysql> explain select * from tab_with_index where name = 1 \G
- *************************** 1. row ***************************
- id: 1
- select_type: SIMPLE
- table: tab_with_index
- type: ALL
- possible_keys: name
- key: NULL
- key_len: NULL
- ref: NULL
- rows: 4
- Extra: Using where
- 1 row in set (0.00 sec)
- mysql> explain select * from tab_with_index where name = '1' \G
- *************************** 1. row ***************************
- id: 1
- select_type: SIMPLE
- table: tab_with_index
- type: ref
- possible_keys: name
- key: name
- key_len: 23
- ref: const
- rows: 1
- Extra: Using where
- 1 row in set (0.00 sec)
mysql> alter table tab_no_index add index name(name);
Query OK, 4 rows affected (8.06 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> explain select * from tab_with_index where name = 1 \G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: tab_with_index
type: ALL
possible_keys: name
key: NULL
key_len: NULL
ref: NULL
rows: 4
Extra: Using where
1 row in set (0.00 sec)
mysql> explain select * from tab_with_index where name = '1' \G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: tab_with_index
type: ref
possible_keys: name
key: name
key_len: 23
ref: const
rows: 1
Extra: Using where
1 row in set (0.00 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 * 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)
|
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)
|
- ......
- SET TIMESTAMP=1169175130;
- BEGIN;
- # at 274
- #070119 10:51:57 server id 1 end_log_pos 105 Query thread_id=1 exec_time=0 error_code=0
- SET TIMESTAMP=1169175117;
- update source_tab set name = '8' where name = '1';
- # at 379
- #070119 10:52:10 server id 1 end_log_pos 406 Xid = 5
- COMMIT;
- # at 406
- #070119 10:52:14 server id 1 end_log_pos 474 Query thread_id=2 exec_time=0 error_code=0
- SET TIMESTAMP=1169175134;
- BEGIN;
- # at 474
- #070119 10:51:29 server id 1 end_log_pos 119 Query thread_id=2 exec_time=0 error_code=0
- SET TIMESTAMP=1169175089;
- insert into target_tab select d1,name from source_tab where name = '1';
- # at 593
- #070119 10:52:14 server id 1 end_log_pos 620 Xid = 7
- COMMIT;
- ......
......
SET TIMESTAMP=1169175130;
BEGIN;
# at 274
#070119 10:51:57 server id 1 end_log_pos 105 Query thread_id=1 exec_time=0 error_code=0
SET TIMESTAMP=1169175117;
update source_tab set name = '8' where name = '1';
# at 379
#070119 10:52:10 server id 1 end_log_pos 406 Xid = 5
COMMIT;
# at 406
#070119 10:52:14 server id 1 end_log_pos 474 Query thread_id=2 exec_time=0 error_code=0
SET TIMESTAMP=1169175134;
BEGIN;
# at 474
#070119 10:51:29 server id 1 end_log_pos 119 Query thread_id=2 exec_time=0 error_code=0
SET TIMESTAMP=1169175089;
insert into target_tab select d1,name from source_tab where name = '1';
# at 593
#070119 10:52:14 server id 1 end_log_pos 620 Xid = 7
COMMIT;
......
- 一是采取上面示例中的做法,将innodb_locks_unsafe_for_binlog的值设置为“on”,强制MySQL使用多版本数据一致性读。但付出的代价是可能无法用binlog正确地恢复或复制数据,因此,不推荐使用这种方式。
- 二是通过使用“select * from source_tab ... Into outfile”和“load data infile ...”语句组合来间接实现,采用这种方式MySQL不会给source_tab加锁。
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 |
SESSION TRANSACTION ISOLATION LEVEL SERIALIZABLE动态改变隔离级别的方式满足需求。
- 第一种情况是:事务需要更新大部分或全部数据,表又比较大,如果使用默认的行锁,不仅这个事务执行效率低,而且可能造成其他事务长时间锁等待和锁冲突,这种情况下可以考虑使用表锁来提高该事务的执行速度。
- 第二种情况是:事务涉及多个表,比较复杂,很可能引起死锁,造成大量事务回滚。这种情况也可以考虑一次性锁定事务涉及的表,从而避免死锁、减少数据库因事务回滚带来的开销。
- SET AUTOCOMMIT=0;
- LOCK TABLES t1 WRITE, t2 READ, ...;
- [do something with tables t1 and t2 here];
- COMMIT;
- UNLOCK TABLES;
SET AUTOCOMMIT=0;
LOCK TABLES t1 WRITE, t2 READ, ...;
[do something with tables t1 and t2 here];
COMMIT;
UNLOCK TABLES;
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> show innodb status \G
- …….
- ------------------------
- LATEST DETECTED DEADLOCK
- ------------------------
- 070710 14:05:16
- *** (1) TRANSACTION:
- TRANSACTION 0 117470078, ACTIVE 117 sec, process no 1468, OS thread id 1197328736 inserting
- mysql tables in use 1, locked 1
- LOCK WAIT 5 lock struct(s), heap size 1216
- MySQL thread id 7521657, query id 673468054 localhost root update
- insert into country (country_id,country) values(110,'Test')
- ………
- *** (2) TRANSACTION:
- TRANSACTION 0 117470079, ACTIVE 39 sec, process no 1468, OS thread id 1164048736 starting index read, thread declared inside InnoDB 500
- mysql tables in use 1, locked 1
- 4 lock struct(s), heap size 1216, undo log entries 1
- MySQL thread id 7521664, query id 673468058 localhost root statistics
- select first_name,last_name from actor where actor_id = 1 for update
- *** (2) HOLDS THE LOCK(S):
- ………
- *** (2) WAITING FOR THIS LOCK TO BE GRANTED:
- ………
- *** WE ROLL BACK TRANSACTION (1)
- ……
mysql> show innodb status \G
…….
------------------------
LATEST DETECTED DEADLOCK
------------------------
070710 14:05:16
*** (1) TRANSACTION:
TRANSACTION 0 117470078, ACTIVE 117 sec, process no 1468, OS thread id 1197328736 inserting
mysql tables in use 1, locked 1
LOCK WAIT 5 lock struct(s), heap size 1216
MySQL thread id 7521657, query id 673468054 localhost root update
insert into country (country_id,country) values(110,'Test')
………
*** (2) TRANSACTION:
TRANSACTION 0 117470079, ACTIVE 39 sec, process no 1468, OS thread id 1164048736 starting index read, thread declared inside InnoDB 500
mysql tables in use 1, locked 1
4 lock struct(s), heap size 1216, undo log entries 1
MySQL thread id 7521664, query id 673468058 localhost root statistics
select first_name,last_name from actor where actor_id = 1 for update
*** (2) HOLDS THE LOCK(S):
………
*** (2) WAITING FOR THIS LOCK TO BE GRANTED:
………
*** WE ROLL BACK TRANSACTION (1)
……
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