自建MySQL 5.7
innodb_autoinc_lock_mode=1
CREATE TABLE `t1` ( `id` int(11) NOT NULL AUTO_INCREMENT, `name` varchar(200) DEFAULT NULL, PRIMARY KEY (`id`), UNIQUE KEY `uqi_name` (`name`) ) ENGINE=InnoDB AUTO_INCREMENT=26 DEFAULT CHARSET=utf8
CREATE TABLE `tt` ( `id` int(11) DEFAULT NULL ) ENGINE=InnoDB DEFAULT CHARSET=utf8
mysql> insert into tt values(1),(2),(3),(4),(5),(6),(7),(8),(9),(10); Query OK, 10 rows affected (0.00 sec) Records: 10 Duplicates: 0 Warnings: 0
session-1:
mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql> insert into t1(name) select *from tt where id<=5; Query OK, 5 rows affected (0.01 sec) Records: 5 Duplicates: 0 Warnings: 0 mysql>
session-2(处理锁等待状态):
mysql> insert into t1(name) select *from tt where id<=5; 等待中...
session-1(显示插入成功):
mysql> insert into t1(name) select *from tt where id>5; Query OK, 5 rows affected (0.00 sec) Records: 5 Duplicates: 0 Warnings: 0 mysql>
session-2(已经提示死锁回滚):
mysql> insert into t1(name) select *from tt where id<=5; ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction
------------------------ LATEST DETECTED DEADLOCK ------------------------ 2022-06-24 22:47:54 0x7f87505f3700 *** (1) TRANSACTION: TRANSACTION 11872922, ACTIVE 40 sec inserting mysql tables in use 2, locked 1 LOCK WAIT 3 lock struct(s), heap size 1136, 1 row lock(s), undo log entries 1 MySQL thread id 4, OS thread handle 140219145197312, query id 207 127.0.0.1 root Sending data insert into t1(name) select *from tt where id<=5 *** (1) WAITING FOR THIS LOCK TO BE GRANTED: RECORD LOCKS space id 743 page no 4 n bits 72 index uqi_name of table `ceshi`.`t1` trx id 11872922 lock mode S waiting Record lock, heap no 2 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 1; hex 31; asc 1;; 1: len 4; hex 8000001a; asc ;; *** (2) TRANSACTION: TRANSACTION 11872917, ACTIVE 100 sec setting auto-inc lock mysql tables in use 2, locked 1 3 lock struct(s), heap size 1136, 1 row lock(s), undo log entries 5 MySQL thread id 3, OS thread handle 140219145729792, query id 208 127.0.0.1 root Sending data insert into t1(name) select *from tt where id>5 *** (2) HOLDS THE LOCK(S): RECORD LOCKS space id 743 page no 4 n bits 72 index uqi_name of table `ceshi`.`t1` trx id 11872917 lock_mode X locks rec but not gap Record lock, heap no 2 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 1; hex 31; asc 1;; 1: len 4; hex 8000001a; asc ;; *** (2) WAITING FOR THIS LOCK TO BE GRANTED: TABLE LOCK table `ceshi`.`t1` trx id 11872917 lock mode AUTO-INC waiting *** WE ROLL BACK TRANSACTION (1)
1、session-1先插入数据
2、session-2 插入数据一定要产生行锁等待,此时自增锁并没有释放,还是持有这个表的自增锁。
3、session-1 写入任意数据(不能指定自增值),会去申请自增锁,但自增锁又被 seesion-2 会话持有。session-2 又在等session-1 释放行锁。
3、锁等待环路发生,MySQL自动杀掉回滚成本较小的会话。