MySQL 5.6.26高并发死锁

Question

表结构：

CREATE TABLE `extend_0` ( 
`id` bigint(20) NOT NULL, 
`code` varchar(30) NOT NULL, 
`data_key` varchar(50) NOT NULL, 
`data_value` varchar(200) NOT NULL, 
`create_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP, 
`update_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP, 
`yn` tinyint(3) NOT NULL DEFAULT '1', 
PRIMARY KEY (`id`,`create_time`), 
UNIQUE KEY `idx_unq_code_data_key` (`code`,`data_key`,`create_time`) USING BTREE, 
KEY `idx_code` (`code`) USING BTREE 
) ENGINE=InnoDB;

当两个事务同时删除和插入相同的数据时，有时会发生死锁。tx_isolation为RR。

例如：

DELETE FROM extend_0 WHERE code = '00226915986' AND yn = 1; 

INSERT INTO extend_0 (id, code, data_key, data_value, create_time) VALUES (1133296779049299970, '00226915986', 'consignWare', 'food', '2019-05-28 16:59:42.418'), (1133296779049299971, '00226915986', 'productType', '0001,0006', '2019-05-28 16:59:42.418'); 

死锁日志：

------------------------------------------------------------------------------ 
2019-05-30 14:48:07 0x7fbb7872c700 
*** (1) TRANSACTION: 
TRANSACTION 125554670, ACTIVE 0 sec starting index read 
mysql tables in use 1, locked 1 
LOCK WAIT 2 lock struct(s), heap size 1136, 1 row lock(s) 
MySQL thread id 5148727, OS thread handle 140443189679872, query id 6111057236 192.168.162.16 waybill updating 
DELETE FROM extend_0 WHERE code = '00226915986' AND yn = 1 
*** (1) WAITING FOR THIS LOCK TO BE GRANTED: 
RECORD LOCKS space id 77 page no 3145 n bits 360 index idx_unq_code_data_key of table `waybill_0`.`extend_0` trx id 125554670 lock_mode X waiting 
Record lock, heap no 285 PHYSICAL RECORD: n_fields 4; compact format; info bits 32 
0: len 15; hex 4a4456433030323236393135393836; asc 00226915986;; 
1: len 11; hex 636f6e7369676e57617265; asc consignWare;; 
2: len 4; hex 5cecf87e; asc \ ~;; 
3: len 8; hex 911d8ce2e1ddf000; asc ;; 

*** (2) TRANSACTION: 
TRANSACTION 125554668, ACTIVE 0 sec inserting 
mysql tables in use 1, locked 1 
5 lock struct(s), heap size 1136, 6 row lock(s), undo log entries 3 
MySQL thread id 5148728, OS thread handle 140443156399872, query id 6111057237 192.168.162.16 waybill update 
INSERT INTO extend_0 (id, code, data_key, data_value, create_time) VALUES (i-1, '00226915986', 'consignWare', 'food', '2019-05-28 16:59:42.418'), (i, '00226915986', 'productType', '0001,0006', '2019-05-28 16:59:42.418') 
*** (2) HOLDS THE LOCK(S): 
RECORD LOCKS space id 77 page no 3145 n bits 360 index idx_unq_code_data_key of table `waybill_0`.`extend_0` trx id 125554668 lock_mode X 
Record lock, heap no 285 PHYSICAL RECORD: n_fields 4; compact format; info bits 32 
0: len 15; hex 4a4456433030323236393135393836; asc 00226915986;; 
1: len 11; hex 636f6e7369676e57617265; asc consignWare;; 
2: len 4; hex 5cecf87e; asc \ ~;; 
3: len 8; hex 911d8ce2e1ddf000; asc ;; 

Record lock, heap no 287 PHYSICAL RECORD: n_fields 4; compact format; info bits 32 
0: len 15; hex 4a4456433030323236393135393836; asc 00226915986;; 
1: len 11; hex 70726f6475637454797065; asc productType;; 
2: len 4; hex 5cecf87e; asc \ ~;; 
3: len 8; hex 911d8ce2e1ddf020; asc ;; 

*** (2) WAITING FOR THIS LOCK TO BE GRANTED: 
RECORD LOCKS space id 77 page no 3145 n bits 360 index idx_unq_waybill_code_data_key of table `waybill_0`.`extend_0` trx id 125554668 lock_mode X locks gap before rec insert intention waiting 
Record lock, heap no 285 PHYSICAL RECORD: n_fields 4; compact format; info bits 32 
0: len 15; hex 4a4456433030323236393135393836; asc JDVC00226915986;; 
1: len 11; hex 636f6e7369676e57617265; asc consignWare;; 
2: len 4; hex 5cecf87e; asc \ ~;; 
3: len 8; hex 911d8ce2e1ddf000; asc ;; 

*** WE ROLL BACK TRANSACTION (1) 
------------------------------------------------------------------------------ 

transaction2已经有lock_mode X了。为什么"lock_mode X锁定空白在rec插入意图等待“发生？

但是，当我们逐一执行事务时，不会出现死锁。例如：

step1: tx1 begin; delete.....;
step2: tx2 begin; delete.....;
step3: tx1 insert....;
step4: tx2 insert....;
step5: tx1 commit;

死锁只有在并发性高的情况下才会发生，死锁似乎是由tx1's delete和tx2's插入的并发造成的。

Answer 1

您正在删除与插入的记录完全相同的记录(通过code)。这就是服务器死锁的原因，因为mysql现在可以知道应该采取哪种操作。您需要使用基于业务案例的适当操作来处理应用程序中的此错误。

没有魔法可以避免这种情况。索引已经在code上了

Answer 2

这个问题看起来和我的变体非常相似。据我所知，在delete语句中有一个问题是完全扫描的。您没有索引和delete语句试图对表进行完全扫描，富尔扫描在表中的所有行上应用锁，甚至对插入中未提交的行也是如此。

MySQL/innodb试图从并行事务锁定未提交的行，结果导致死锁

尝试为代码和yn文件创建索引。索引可以减少死锁事件。确保删除使用索引而不是完全扫描。