MySQL死锁检测和回滚

”

在innodb源代码lock/lock0lock.c文件中,定义了两个常量:

/* Restricts the length of search we will do in the waits-for

     graph of transactions */

#define LOCK_MAX_N_STEPS_IN_DEADLOCK_CHECK 1000000

 

/* Restricts the recursion depth of the search we will do in the waits-for

    graph of transactions */

#define LOCK_MAX_DEPTH_IN_DEADLOCK_CHECK 200

然后在检查是否产生死锁的函数lock_deadlock_occurs()中有如下代码:

 

ret = lock_deadlock_recursive(trx, trx, lock, &cost, 0);

switch (ret) {

case LOCK_EXCEED_MAX_DEPTH:

        产生死锁
        ...

        break;

}

其中的lock_deadlock_recursive()函数是递归函数,它会检查自身递归深度,其中有如下代码:

 

ibool   too_far

   = depth > LOCK_MAX_DEPTH_IN_DEADLOCK_CHECK

|| *cost > LOCK_MAX_N_STEPS_IN_DEADLOCK_CHECK;

...

if (too_far) {

                return(LOCK_EXCEED_MAX_DEPTH);

            }

因此innodb在检查是否产生死锁时调用lock_deadlock_occurs()检查,这个函数再会调用lock_deadlock_recursive()递归检查锁的数目(不知道这么说是否确切?)，当递归的深度depth大于了一开始介绍的常量LOCK_MAX_DEPTH_IN_DEADLOCK_CHECK,或者cost(不清楚这个代表什么)大于一开始介绍的常量LOCK_MAX_N_STEPS_IN_DEADLOCK_CHECK时,就认为发生了死锁.

资料出处：

http://blog.csdn.net/sunmun/article/details/50088381

https://dev.mysql.com/doc/refman/5.7/en/innodb-deadlock-detection.html

http://www.cnblogs.com/zemliu/p/3502395.html 

MySQL死锁检测和回滚

标签：output   ase   innodb   dead   actions   htm   details   递归   mysql死锁