我的表非常简单：
CREATE TABLE `d` (
`id` int(11) DEFAULT NULL,
UNIQUE KEY `id` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
没有记录：
select * from d;
Empty set (0,01 sec)
然后我尝试在不同的会话中打开两个交易：
会话＃1：
begin;
Query OK, 0 rows affected (0,00 sec)
select * from d where id = 100 for update;
Empty set (0,00 sec)
会话＃2：
begin;
Query OK, 0 rows affected (0,00 sec)
select * from d where id = 700 for update;
Empty set (0,00 sec)
现在我尝试在会话＃2 和会话＆＃34;冻结＆＃34;
中插入新记录insert into d values (700);
当我尝试在会话＃1 中执行相同操作（使用其他ID字段）时，它会崩溃：
insert into d values (100); --> ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction in Session #1
insert into d values (700); --> Query OK, 1 row affected (4,08 sec) in Session #2
我该如何解决僵局？ InnoDB状态为：
------------------------
LATEST DETECTED DEADLOCK
------------------------
2017-07-06 15:59:25 0x70000350d000
*** (1) TRANSACTION:
TRANSACTION 43567, ACTIVE 15 sec inserting
mysql tables in use 1, locked 1
LOCK WAIT 3 lock struct(s), heap size 1136, 2 row lock(s), undo log entries 1
MySQL thread id 4, OS thread handle 123145358217216, query id 89 localhost root update
insert into d values (700)
*** (1) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 126 page no 4 n bits 72 index id of table `trx`.`d` trx id 43567 lock_mode X insert intention waiting
Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 0
0: len 8; hex 73757072656d756d; asc supremum;;
*** (2) TRANSACTION:
TRANSACTION 43568, ACTIVE 7 sec inserting
mysql tables in use 1, locked 1
3 lock struct(s), heap size 1136, 2 row lock(s), undo log entries 1
MySQL thread id 3, OS thread handle 123145357938688, query id 90 localhost root update
insert into d values (100)
*** (2) HOLDS THE LOCK(S):
RECORD LOCKS space id 126 page no 4 n bits 72 index id of table `trx`.`d` trx id 43568 lock_mode X
Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 0
0: len 8; hex 73757072656d756d; asc supremum;;
*** (2) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 126 page no 4 n bits 72 index id of table `trx`.`d` trx id 43568 lock_mode X insert intention waiting
Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 0
0: len 8; hex 73757072656d756d; asc supremum;;
*** WE ROLL BACK TRANSACTION (2)
答案 0 :(得分：2)
此死锁错误是MySQL InnoDB引擎中的错误，已在12年内未得到修复。 （缺陷号25847：https://bugs.mysql.com/bug.php?id=25847，解决方法：How do I lock on an InnoDB row that doesn't exist yet?）它与唯一密钥无关。运行此查询也将导致相同的死锁错误。
Session #1: CREATE TABLE t (id int) ENGINE=InnoDB;
Session #1: SET AUTOCOMMIT = 0;
Session #1: SELECT id FROM t WHERE id = 1 FOR UPDATE;
Session #2: SET AUTOCOMMIT = 0;
Session #2: SELECT id FROM t WHERE id = 2 FOR UPDATE;
Session #1: INSERT INTO t (id) VALUES (1); -- Hang
Session #2: INSERT INTO t (id) VALUES (2); -- Session #1: OK, Session #2: Deadlock found when trying to get lock; try restarting transaction
InnoDB状态相同：
------------------------
LATEST DETECTED DEADLOCK
------------------------
2019-10-24 00:25:31 0x1638
*** (1) TRANSACTION:
TRANSACTION 1287, ACTIVE 62 sec inserting
mysql tables in use 1, locked 1
LOCK WAIT 3 lock struct(s), heap size 1136, 2 row lock(s)
MySQL thread id 7, OS thread handle 9444, query id 143 localhost ::1 root update
INSERT INTO t (id) VALUES (1)
*** (1) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 23 page no 3 n bits 72 index GEN_CLUST_INDEX of table `test`.`t` trx id 1287 lock_mode X insert intention waiting
Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 0
0: len 8; hex 73757072656d756d; asc supremum;;
*** (2) TRANSACTION:
TRANSACTION 1288, ACTIVE 19 sec inserting, thread declared inside InnoDB 5000
mysql tables in use 1, locked 1
3 lock struct(s), heap size 1136, 2 row lock(s)
MySQL thread id 9, OS thread handle 5688, query id 145 localhost ::1 root update
INSERT INTO t (id) VALUES (2)
*** (2) HOLDS THE LOCK(S):
RECORD LOCKS space id 23 page no 3 n bits 72 index GEN_CLUST_INDEX of table `test`.`t` trx id 1288 lock_mode X
Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 0
0: len 8; hex 73757072656d756d; asc supremum;;
*** (2) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 23 page no 3 n bits 72 index GEN_CLUST_INDEX of table `test`.`t` trx id 1288 lock_mode X insert intention waiting
Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 0
0: len 8; hex 73757072656d756d; asc supremum;;
*** WE ROLL BACK TRANSACTION (2)
答案 1 :(得分：1)
请注意，从MySQL 8.0.1开始， 性能模式暴露了innodb数据锁。
请参阅https://dev.mysql.com/doc/refman/8.0/en/data-locks-table.html
请参阅https://dev.mysql.com/doc/refman/8.0/en/data-lock-waits-table.html
在此示例中，仅在会话1中第一次选择后，锁定为：
mysql> select * from performance_schema.data_locks \G
*************************** 1. row ***************************
ENGINE: INNODB
ENGINE_LOCK_ID: 1808:76
ENGINE_TRANSACTION_ID: 1808
THREAD_ID: 35
EVENT_ID: 13081
OBJECT_SCHEMA: test
OBJECT_NAME: d
PARTITION_NAME: NULL
SUBPARTITION_NAME: NULL
INDEX_NAME: NULL
OBJECT_INSTANCE_BEGIN: 139756088373592
LOCK_TYPE: TABLE
LOCK_MODE: IX
LOCK_STATUS: GRANTED
LOCK_DATA: NULL
*************************** 2. row ***************************
ENGINE: INNODB
ENGINE_LOCK_ID: 1808:2:5:1
ENGINE_TRANSACTION_ID: 1808
THREAD_ID: 35
EVENT_ID: 13111
OBJECT_SCHEMA: test
OBJECT_NAME: d
PARTITION_NAME: NULL
SUBPARTITION_NAME: NULL
INDEX_NAME: id
OBJECT_INSTANCE_BEGIN: 139756088370552
LOCK_TYPE: RECORD
LOCK_MODE: X
LOCK_STATUS: GRANTED
LOCK_DATA: supremum pseudo-record <--- HERE
2 rows in set (0.00 sec)
这不是死锁本身的解决方案，但是对锁定的可见性对于理解这个问题还有很长的路要走。
这里，SELECT FOR UPDATE都锁定＆＃34; suprenum＆＃34;记录，因为id 100和700大于表中的最大ID（它是空的）。
一旦有更多记录（比如ID = 500），两个查询应该同时执行，因为ID中的不同间隙将被锁定。
答案 2 :(得分：1)
我怀疑发生了死锁，因为InnoDB在处理“差距”时保守。请注意，100和700都在未触及的土地的同一个模糊区域。 InnoDB不能（或至少不）处理“100”和“700”不同的事实。 InnoDB希望标记单个行，但表中没有已包含这些ID的行。
交易2可能会超时（见innodb_lock_wait_timeout）。当你第二次使用＃2进行交易时，＃2仍然想要一个锁定，InnoDB就会受到惩罚并放弃。
底线：与死锁一起生活。当它们发生时，请回到BEGIN。你发现了另一个不明显的情况，即发生了不必要的死锁。
此外，我怀疑修复此案例的代码会减慢大多数其他情况，并导致一系列错误，需要多个版本才能发现并修复。