MySQL版本8.0，隔离级别RR和RC均能复现。
CREATE TABLE `t2` (
`a` int NOT NULL,
`b` int DEFAULT NULL,
`c` int DEFAULT NULL,
PRIMARY KEY (`a`),
UNIQUE KEY `b` (`b`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
insert into t2 values(1,1,1);
| time | session1 | session2 | session3 |
|---|---|---|---|
| t1 | begin;update t2 set c=2 where b=1; | ||
| t2 | begin;delete from t2 where a=1; | ||
| t3 | begin;delete from t2 where b=1; | ||
| t4 | rollback; | ||
| t5 | Query OK, 1 row affected | (1213, ‘Deadlock found when trying to get lock; try restarting transaction‘) |
MySQL root@127.0.0.1:performance_schema> select ENGINE_TRANSACTION_ID,THREAD_ID,OBJECT_SCHEMA,OBJECT_NAME,INDEX_NAME,LOCK_TYPE,LOCK_MODE,LOCK_S
-> TATUS,LOCK_DATA from performance_schema.data_locks;
+-----------------------+-----------+---------------+-------------+------------+-----------+---------------+-------------+-----------+
| ENGINE_TRANSACTION_ID | THREAD_ID | OBJECT_SCHEMA | OBJECT_NAME | INDEX_NAME | LOCK_TYPE | LOCK_MODE | LOCK_STATUS | LOCK_DATA |
+-----------------------+-----------+---------------+-------------+------------+-----------+---------------+-------------+-----------+
| 6689 | 68 | test | t2 | <null> | TABLE | IX | GRANTED | <null> |
| 6689 | 68 | test | t2 | b | RECORD | X,REC_NOT_GAP | GRANTED | 1, 1 |
| 6689 | 68 | test | t2 | PRIMARY | RECORD | X,REC_NOT_GAP | GRANTED | 1 |
+-----------------------+-----------+---------------+-------------+------------+-----------+---------------+-------------+-----------+
常看performance_schema库下的data_locks表，t1时刻对表t2主键和唯一索引b上加了两个记录锁，X,REC_NOT_GAP代表不是gap锁和next-key lock，GRANTED代表已经被授予，ENGINE_TRANSACTION_ID代表事务id号。
+-----------------------+-----------+---------------+-------------+------------+-----------+---------------+-------------+-----------+
| ENGINE_TRANSACTION_ID | THREAD_ID | OBJECT_SCHEMA | OBJECT_NAME | INDEX_NAME | LOCK_TYPE | LOCK_MODE | LOCK_STATUS | LOCK_DATA |
+-----------------------+-----------+---------------+-------------+------------+-----------+---------------+-------------+-----------+
| 6690 | 67 | test | t2 | <null> | TABLE | IX | GRANTED | <null> |
| 6690 | 67 | test | t2 | PRIMARY | RECORD | X,REC_NOT_GAP | WAITING | 1 |
| 6689 | 68 | test | t2 | <null> | TABLE | IX | GRANTED | <null> |
| 6689 | 68 | test | t2 | b | RECORD | X,REC_NOT_GAP | GRANTED | 1, 1 |
| 6689 | 68 | test | t2 | PRIMARY | RECORD | X,REC_NOT_GAP | GRANTED | 1 |
+-----------------------+-----------+---------------+-------------+------------+-----------+---------------+-------------+-----------+
t2时刻，对t2主键索引为1的记录也要加x record lock，此时锁处于等待，session1主键为1的记录上锁还未释放。
t3时刻
+-----------------------+-----------+---------------+-------------+------------+-----------+---------------+-------------+-----------+
| ENGINE_TRANSACTION_ID | THREAD_ID | OBJECT_SCHEMA | OBJECT_NAME | INDEX_NAME | LOCK_TYPE | LOCK_MODE | LOCK_STATUS | LOCK_DATA |
+-----------------------+-----------+---------------+-------------+------------+-----------+---------------+-------------+-----------+
| 6691 | 66 | test | t2 | <null> | TABLE | IX | GRANTED | <null> |
| 6691 | 66 | test | t2 | b | RECORD | X,REC_NOT_GAP | WAITING | 1, 1 |
| 6690 | 67 | test | t2 | <null> | TABLE | IX | GRANTED | <null> |
| 6690 | 67 | test | t2 | PRIMARY | RECORD | X,REC_NOT_GAP | WAITING | 1 |
| 6689 | 68 | test | t2 | <null> | TABLE | IX | GRANTED | <null> |
| 6689 | 68 | test | t2 | b | RECORD | X,REC_NOT_GAP | GRANTED | 1, 1 |
| 6689 | 68 | test | t2 | PRIMARY | RECORD | X,REC_NOT_GAP | GRANTED | 1 |
+-----------------------+-----------+---------------+-------------+------------+-----------+---------------+-------------+-----------+
t3时刻，对表t2唯一索引b为1的记录也要加x record lock，此时锁处于等待，session1唯一索引b为1的记录上锁还未释放。
t4时刻
session1事务回滚，主键索引和唯一索引b上的锁释放，session2获得了主键索引为1的x record lock，等待唯一索引为1上的x record lock；session3获得了唯一索引为1上的x record lock，主键索引为1的x record lock，发生了死锁
t5时刻
+-----------------------+-----------+---------------+-------------+------------+-----------+---------------+-------------+-----------+
| ENGINE_TRANSACTION_ID | THREAD_ID | OBJECT_SCHEMA | OBJECT_NAME | INDEX_NAME | LOCK_TYPE | LOCK_MODE | LOCK_STATUS | LOCK_DATA |
+-----------------------+-----------+---------------+-------------+------------+-----------+---------------+-------------+-----------+
| 6690 | 67 | test | t2 | <null> | TABLE | IX | GRANTED | <null> |
| 6690 | 67 | test | t2 | PRIMARY | RECORD | X,REC_NOT_GAP | GRANTED | 1 |
| 6690 | 67 | test | t2 | b | RECORD | X,REC_NOT_GAP | GRANTED | 1, 1 |
+-----------------------+-----------+---------------+-------------+------------+-----------+---------------+-------------+-----------+
session3事务回滚，session2获得了表t2主键和唯一索引b上加了两个记录锁。
show engine innodb status\G查看死锁信息
------------------------
LATEST DETECTED DEADLOCK
------------------------
2021-06-25 13:18:39 0x7f7dd6fd0700
*** (1) TRANSACTION:
TRANSACTION 6691, ACTIVE 84 sec starting index read
mysql tables in use 1, locked 1
LOCK WAIT 3 lock struct(s), heap size 1136, 3 row lock(s)
MySQL thread id 27, OS thread handle 140179212433152, query id 147 127.0.0.1 root updating
delete from t2 where b=1
*** (1) HOLDS THE LOCK(S):
RECORD LOCKS space id 4 page no 5 n bits 72 index b of table `test`.`t2` trx id 6691 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 4; hex 80000001; asc ;;
1: len 4; hex 80000001; asc ;;
*** (1) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 4 page no 4 n bits 72 index PRIMARY of table `test`.`t2` trx id 6691 lock_mode X locks rec but not gap waiting
Record lock, heap no 2 PHYSICAL RECORD: n_fields 5; compact format; info bits 32
0: len 4; hex 80000001; asc ;;
1: len 6; hex 000000001a22; asc ";;
2: len 7; hex 020000011e0151; asc Q;;
3: len 4; hex 80000001; asc ;;
4: len 4; hex 80000001; asc ;;
*** (2) TRANSACTION:
TRANSACTION 6690, ACTIVE 111 sec updating or deleting
mysql tables in use 1, locked 1
LOCK WAIT 3 lock struct(s), heap size 1136, 3 row lock(s), undo log entries 1
MySQL thread id 28, OS thread handle 140179212105472, query id 146 127.0.0.1 root updating
delete from t2 where a=1
*** (2) HOLDS THE LOCK(S):
RECORD LOCKS space id 4 page no 4 n bits 72 index PRIMARY of table `test`.`t2` trx id 6690 lock_mode X locks rec but not gap
Record lock, heap no 2 PHYSICAL RECORD: n_fields 5; compact format; info bits 32
0: len 4; hex 80000001; asc ;;
1: len 6; hex 000000001a22; asc ";;
2: len 7; hex 020000011e0151; asc Q;;
3: len 4; hex 80000001; asc ;;
4: len 4; hex 80000001; asc ;;
*** (2) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 4 page no 5 n bits 72 index b of table `test`.`t2` trx id 6690 lock_mode X locks rec but not gap waiting
Record lock, heap no 2 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 80000001; asc ;;
1: len 4; hex 80000001; asc ;;
*** WE ROLL BACK TRANSACTION (1)
4、总结
MySQL8.0通过data_locks这张表，结合show engine innodb status的死锁输出，很容易分析出锁等待和死锁相关信息。
原文：https://www.cnblogs.com/yang417/p/14930539.html