Update和Insert查询之间的死锁

Question

我在Update和Insert查询之间的应用程序中遇到了死锁,我无法理解为什么会以导致死锁的方式给出锁.

环境-

• 应用程序 - Django
• 数据库 - MySQL 5.7
• 发动机 - Innodb
• 隔离级别 - READ COMMITTED.
• 表(为安全而更改名称) -
  1. M - 主键 - id
  2. MSC - 拥有M.id的外键
     • MSC上的索引
       1. M(FK)指数
       2. S(FK)指数
       3. C(FK)指数
       4. 关于唯一约束的索引(M,S,C)

查询-以下两个查询(查询截断,只显示相关列) -

• 更新 -

  UPDATE `MSC` SET `m_id` = 110, `s_id` = 1234, `c_id` = '9b39cd', WHERE `MSC`.`id` = 54362

• 插入 -

  INSERT INTO `MSC` (`m_id`, `s_id`, `c_id`) VALUES (110, 1235, '9b39cd')

僵局-

• 首先触发更新查询,然后触发插入查询,但SHOW ENGINE INNODB STATUS\G;显示插入先前启动的查询的输出.
• 从输出来看,他们执行的时间似乎是以下面的方式导致死锁 -
  • Insert在MSC上获得独占(X)锁并等待外键M上的共享(S)锁.
  • Update获得M上的独占(X)锁定并等待外键MSC上的独占(X)锁定.
• 以下是完整输出 -

    ------------------------
    LATEST DETECTED DEADLOCK
    ------------------------
    2017-03-17 15:41:03 0x7f8039550700
    * (1) TRANSACTION:
    TRANSACTION 7784084, ACTIVE 2 sec inserting
    mysql tables in use 1, locked 1
    LOCK WAIT 11 lock struct(s), heap size 1136, 46 row lock(s), undo log entries 25
    MySQL thread id 493648, OS thread handle 140188693010176, query id 55263589 ip-10-198-7-203.ec2.internal 10.198.7.203 root update
    INSERT INTO MSC (m_id, s_id, c_id) VALUES (110, 1235, '9b39cd')
    * (1) WAITING FOR THIS LOCK TO BE GRANTED:
    RECORD LOCKS space id 1377 page no 10 n bits 152 index PRIMARY of table "db"."M" trx id 7784084 lock mode S locks rec but not gap waiting
    Record lock, heap no 67 PHYSICAL RECORD: n_fields 42; compact format; info bits 0
     0: len 4; hex 800000ac; asc     ;;
     1: len 6; hex 00000076c69f; asc    v  ;;
     2: len 7; hex 76000001cb24c5; asc v    $ ;;
     3: len 8; hex 999be72e2e07032e; asc    ..  .;;
     4: len 8; hex 999c22fa43025221; asc   " C R!;;


*** (2) TRANSACTION:
TRANSACTION 7784095, ACTIVE 0 sec starting index read
mysql tables in use 1, locked 1
6 lock struct(s), heap size 1136, 3 row lock(s), undo log entries 2
MySQL thread id 493645, OS thread handle 140188694415104, query id 55263635 ip-10-198-3-73.ec2.internal 10.198.3.73 root updating
UPDATE `MSC` SET `m_id` = 110, `s_id` = 1234, `c_id` = '9b39cd', WHERE `MSC`.`id` = 54362
*** (2) HOLDS THE LOCK(S):
RECORD LOCKS space id 1377 page no 10 n bits 152 index PRIMARY of table "db"."M" trx id 7784095 lock_mode X locks rec but not gap
Record lock, heap no 67 PHYSICAL RECORD: n_fields 42; compact format; info bits 0
 0: len 4; hex 800000ac; asc     ;;
 1: len 6; hex 00000076c69f; asc    v  ;;
 2: len 7; hex 76000001cb24c5; asc v    $ ;;
 3: len 8; hex 999be72e2e07032e; asc    ..  .;;
 4: len 8; hex 999c22fa43025221; asc   " C R!;;

*** (2) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 1410 page no 261 n bits 104 index PRIMARY of table "db"."MSC" trx id 7784095 lock_mode X locks rec but not gap waiting
Record lock, heap no 16 PHYSICAL RECORD: n_fields 16; compact format; info bits 0
 0: len 4; hex 800038e2; asc   8 ;;
 1: len 6; hex 00000076c694; asc    v  ;;
 2: len 7; hex 6f0000055b2a0e; asc o   [* ;;
 3: len 8; hex 999c22fa0d08a51c; asc   "     ;;
 4: len 8; hex 999c22fa3b0dffd8; asc   " ;   ;;

*** WE ROLL BACK TRANSACTION (2)

问题 - 我无法理解以下内容 - 1.为什么更新查询必须等待并且在插入查询得到锁定时无法获取锁定？2.为什么更新查询需要/采用M表上的独占(X)锁定.

请在这里分享您的想法.如果需要任何额外信息,请告诉我.

Answer 1

M表中是否存在id值110？此外，将这些单独的事务包装在START TRANSACTION;和COMMIT;命令中可能会很有用，以确保插入在更新尝试运行之前完成。

例子：

START TRANSACTION;
INSERT INTO `MSC` (`m_id`, `s_id`, `c_id`) VALUES (110, 1235, '9b39cd')
COMMIT;

START TRANSACTION;
UPDATE `MSC` SET `m_id` = 110, `s_id` = 1234, `c_id` = '9b39cd', WHERE 
`MSC`.`id` = 54362
COMMIT;