mysql死锁示例

时间:2024-01-09 08:50:02

MySQL有三种锁的级别:页级、表级、行级。
MyISAM和MEMORY存储引擎采用的是表级锁(table-level locking);BDB存储引擎采用的是页面锁(page-level
locking),但也支持表级锁;InnoDB存储引擎既支持行级锁(row-level locking),也支持表级锁,但默认情况下是采用行级锁。
MySQL这3种锁的特性可大致归纳如下:
表级锁:开销小,加锁快;不会出现死锁;锁定粒度大,发生锁冲突的概率最高,并发度最低。
行级锁:开销大,加锁慢;会出现死锁;锁定粒度最小,发生锁冲突的概率最低,并发度也最高。
页面锁:开销和加锁时间界于表锁和行锁之间;会出现死锁;锁定粒度界于表锁和行锁之间,并发度一般。

示例1:

-- 按行获取行锁
-- 获取主键的共享锁
insert into logging_exceptionlog_history_id_2 SELECT * from logging_exceptionlog_history_id;
-- 获取主键的互斥锁
delete from logging_exceptionlog_history_id where id > 100 and id < 1000;

show engine innodb status;   查看innodb引擎状态,可查看最近的死锁情况

mysql死锁示例

示例2:

表t1

CREATE TABLE `t1` (
  `ID` int(11) NOT NULL AUTO_INCREMENT,
  `Name` varchar(64) DEFAULT NULL,
  `Age` int(11) DEFAULT NULL,
  `PostTime` timestamp NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (`ID`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;

会话1
-- 全局的自动提交设为0,即不自动提交,然后另开一个会话查询autocommit状态,当前会话可能还没起作用
set GLOBAL autocommit = 0;

会话2

-- 另开一个会话查询autocommit状态

show VARIABLES like '%autocommit%';

-- 插入一条记录
INSERT into t1(Name, Age) values('xxx', 23);

会话3

show VARIABLES like '%autocommit%';
-- 使用共享锁查询表,注意一定要加上 lock in share mode,否则不会出现死锁
select * from t1 lock in share mode;

查看

select * from INNODB_LOCK_WAITS;

mysql死锁示例

select * from INNODB_LOCKS;

mysql死锁示例

select * from INNODB_TRX;

mysql死锁示例

连接查询, 只需要使用这个sql即可查询上述三表的信息

select a.requesting_trx_id, c.lock_mode as wait_lock_mode,
c.lock_type as wait_lock_type, c.lock_table as wait_lock_table,
c.lock_index as wait_lock_index, c.lock_data as wait_lock_data,
e.trx_state as wait_trx_state, e.trx_query as wait_trx_query,
a.blocking_trx_id,b.lock_mode as block_lock_mode, b.lock_type as block_lock_type,
b.lock_table as block_lock_table, b.lock_index as block_lock_index, b.lock_data as block_lock_data,
d.trx_state as block_trx_state, d.trx_query as block_trx_query
from information_schema.INNODB_LOCK_WAITS a
     INNER JOIN information_schema.INNODB_LOCKS b on a.blocking_lock_id = b.lock_id
     INNER JOIN information_schema.INNODB_LOCKS c on a.requested_lock_id = c.lock_id
     INNER JOIN information_schema.INNODB_TRX d on a.blocking_trx_id = d.trx_id
     INNER JOIN information_schema.INNODB_TRX e on a.requesting_trx_id = e.trx_id

mysql死锁示例