欢迎关注我的《深入理解MySQL主从原理 32讲 》，如下：  如果图片不能显示可查看下面链接： https://www.jianshu.com/p/d636215d767f ###一、问题由来 这是我同事问我的一个问题，在网上看到了如下案例，本案例RC RR都可以出现，其实这个死锁原因也不叫简单，我们来具体看看： #####构造数据 ``` CREATE database deadlock_test; use deadlock_test; CREATE TABLE `push_token` ( `id` bigint(20) NOT NULL AUTO_INCREMENT, `token` varchar(128) NOT NULL COMMENT 'push token', `app_id` varchar(128) DEFAULT NULL COMMENT 'appid', `deleted` tinyint(1) NOT NULL COMMENT '是否已删除 0：否 1：是', PRIMARY KEY (`id`), UNIQUE KEY `uk_token_appid` (`token`,`app_id`) ) ENGINE=InnoDB AUTO_INCREMENT=3384 DEFAULT CHARSET=utf8 COMMENT='pushtoken表'; insert into push_token (id, token, app_id, deleted) values(1,"token1",1,0); ``` #####操作数据 |s1（TRX_ID367661）|s2（TRX_ID367662）|s3（TRX_ID367663）| |-|-|-| |begin; UPDATE push_token SET deleted = 1 WHERE token = 'token1' AND app_id = '1';||| ||begin; DELETE FROM push_token WHERE id IN (1);|| |||begin; UPDATE push_token SET deleted = 1 WHERE token = 'token1' AND app_id = '1';| |commit;||| |Query OK, 0 rows affected (0.00 sec)| Query OK, 1 row affected (17.32 sec)| ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction| ###二、分析方法 我使用的分析方法是把整个加锁的日志打印出来，当然需要用到我自己做了输出修改的一个版本，如下： https://github.com/gaopengcarl/percona-server-locks-detail-5.7.22 这个版本我打开了的日志记录参数如下： ``` mysql> show variables like '%gaopeng%'; +--------------------------------+-------+ | Variable_name | Value | +--------------------------------+-------+ | gaopeng_mdl_detail | OFF | | innodb_gaopeng_row_lock_detail | ON | +--------------------------------+-------+ 2 rows in set (0.01 sec) ``` 这样大部分的innodb加锁记录都会记录到errlog日志了。好了下面我详细分析一下日志： ###三、分析过程 初始化的情况整个表只有1条记录，本表包含一个主键和一个唯一键。 - ####s1（TRX_ID367661） 执行语句 ``` begin; UPDATE push_token SET deleted = 1 WHERE token = 'token1' AND app_id = '1'; ``` 日志输出： ``` 2019-08-18T19:10:05.117317+08:00 6 [Note] InnoDB: TRX ID:(367661) table:deadlock_test/push_token index:uk_token_appid space_id: 449 page_id:4 heap_no:2 row lock mode:LOCK_X|LOCK_NOT_GAP| PHYSICAL RECORD: n_fields 3; compact format; info bits 0 0: len 6; hex 746f6b656e31; asc token1;; 1: len 1; hex 31; asc 1;; 2: len 8; hex 8000000000000001; asc ;; 2019-08-18T19:10:05.117714+08:00 6 [Note] InnoDB: TRX ID:(367661) table:deadlock_test/push_token index:PRIMARY space_id: 449 page_id:3 heap_no:2 row lock mode:LOCK_X|LOCK_NOT_GAP| PHYSICAL RECORD: n_fields 6; compact format; info bits 0 0: len 8; hex 8000000000000001; asc ;; 1: len 6; hex 000000059c2c; asc ,;; 2: len 7; hex bf000000420110; asc B ;; 3: len 6; hex 746f6b656e31; asc token1;; 4: len 1; hex 31; asc 1;; 5: len 1; hex 80; asc ;; ``` 我们看到主键和唯一键都加锁了如下图：  - ####s2（TRX_ID367662） 执行语句 ``` begin;DELETE FROM push_token WHERE id IN (1); ```` 日志输出： ``` 2019-08-18T19:10:22.751467+08:00 9 [Note] InnoDB: TRX ID:(367662) table:deadlock_test/push_token index:PRIMARY space_id: 449 page_id:3 heap_no:2 row lock mode:LOCK_X|LOCK_NOT_GAP| PHYSICAL RECORD: n_fields 6; compact format; info bits 0 0: len 8; hex 8000000000000001; asc ;; 1: len 6; hex 000000059c2d; asc -;; 2: len 7; hex 400000002a1dc8; asc @ * ;; 3: len 6; hex 746f6b656e31; asc token1;; 4: len 1; hex 31; asc 1;; 5: len 1; hex 81; asc ;; 2019-08-18T19:10:22.752753+08:00 9 [Note] InnoDB: Trx(367662) is blocked!!!!! ``` 这个时候S2需要获取主键上的锁，因此被堵塞了如下图：  - ####s3（TRX_ID367663） 执行语句 ``` begin; UPDATE push_token SET deleted = 1 WHERE token = 'token1' AND app_id = '1'; ```` 日志输出： ``` 019-08-18T19:10:30.822111+08:00 8 [Note] InnoDB: TRX ID:(367663) table:deadlock_test/push_token index:uk_token_appid space_id: 449 page_id:4 heap_no:2 row lock mode:LOCK_X|LOCK_NOT_GAP| PHYSICAL RECORD: n_fields 3; compact format; info bits 0 0: len 6; hex 746f6b656e31; asc token1;; 1: len 1; hex 31; asc 1;; 2: len 8; hex 8000000000000001; asc ;; 2019-08-18T19:10:30.918248+08:00 8 [Note] InnoDB: Trx(367663) is blocked!!!!! ``` 这个时候S3需要获取唯一键上的锁，因此被堵塞了如下图：  - ####s1（TRX_ID367661） 执行语句 这一步完成后死锁出现。 ``` commit; ``` 日志输出如下： ``` 367663和367662各自获取需要的锁 2019-08-18T19:10:36.566733+08:00 8 [Note] InnoDB: TRX ID:(367663) table:deadlock_test/push_token index:uk_token_appid space_id: 449 page_id:4 heap_no:2 row lock mode:LOCK_X|LOCK_NOT_GAP| PHYSICAL RECORD: n_fields 3; compact format; info bits 0 0: len 6; hex 746f6b656e31; asc token1;; 1: len 1; hex 31; asc 1;; 2: len 8; hex 8000000000000001; asc ;; 2019-08-18T19:10:36.568711+08:00 9 [Note] InnoDB: TRX ID:(367662) table:deadlock_test/push_token index:PRIMARY space_id: 449 page_id:3 heap_no:2 row lock mode:LOCK_X|LOCK_NOT_GAP| PHYSICAL RECORD: n_fields 6; compact format; info bits 0 0: len 8; hex 8000000000000001; asc ;; 1: len 6; hex 000000059c2d; asc -;; 2: len 7; hex 400000002a1dc8; asc @ * ;; 3: len 6; hex 746f6b656e31; asc token1;; 4: len 1; hex 31; asc 1;; 5: len 1; hex 81; asc ;; 367663获取主键锁堵塞、367662获取唯一键锁堵塞，死锁形成 2019-08-18T19:10:36.570313+08:00 8 [Note] InnoDB: TRX ID:(367663) table:deadlock_test/push_token index:PRIMARY space_id: 449 page_id:3 heap_no:2 row lock mode:LOCK_X|LOCK_NOT_GAP| PHYSICAL RECORD: n_fields 6; compact format; info bits 0 0: len 8; hex 8000000000000001; asc ;; 1: len 6; hex 000000059c2d; asc -;; 2: len 7; hex 400000002a1dc8; asc @ * ;; 3: len 6; hex 746f6b656e31; asc token1;; 4: len 1; hex 31; asc 1;; 5: len 1; hex 81; asc ;; 2019-08-18T19:10:36.571199+08:00 8 [Note] InnoDB: Trx(367663) is blocked!!!!! 2019-08-18T19:10:36.572481+08:00 9 [Note] InnoDB: TRX ID:(367662) table:deadlock_test/push_token index:uk_token_appid space_id: 449 page_id:4 heap_no:2 row lock mode:LOCK_X|LOCK_NOT_GAP| PHYSICAL RECORD: n_fields 3; compact format; info bits 0 0: len 6; hex 746f6b656e31; asc token1;; 1: len 1; hex 31; asc 1;; 2: len 8; hex 8000000000000001; asc ;; 2019-08-18T19:10:36.573073+08:00 9 [Note] InnoDB: Transactions deadlock detected, dumping detailed information. ``` 这个时候我们看到s2和s3先是获取了各自需要的锁，s3获取主键锁堵塞，s2获取唯一键锁堵塞，死锁出现。如下图：  好了我们看到了死锁就这样出现。