Question

我正在尝试解决一个涉及其中一个忙表的死锁的错误。我已经阅读了this SO question关于死锁的内容，虽然它有意义，但在我的情况下，查询顺序似乎不是原因。

以下是SHOW ENGINE INNODB STATUS;的缩写输出：

*** (1) TRANSACTION:
TRANSACTION 1 2611184895, ACTIVE 0 sec, process no 17501, OS thread id 140516779579136 starting index read
mysql tables in use 1, locked 1
LOCK WAIT 2 lock struct(s), heap size 368, 1 row lock(s)
MySQL thread id 211935717, query id 3146186174 [SERVER A] Searching rows for update

UPDATE images_unread_comments
    SET unread = 0
    WHERE user_id = 1 AND comment_id IN(1,2,3) AND unread = 1

*** (1) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 0 page no 404976 n bits 632 index `users_unread_comments` of table images_unread_comments trx id 1 2611184895 lock_mode X waiting
Record lock, heap no 558 PHYSICAL RECORD: n_fields 3; compact format; info bits 32
 0: len 4; hex 0001461a; asc   F ;; 1: len 1; hex 01; asc  ;; 2: len 6; hex 00000e67d888; asc    g  ;;

*** (2) TRANSACTION:
TRANSACTION 1 2611184892, ACTIVE 0 sec, process no 17501, OS thread id 140516774520576 updating or deleting, thread declared inside InnoDB 494
mysql tables in use 1, locked 1
6 lock struct(s), heap size 1216, 11 row lock(s), undo log entries 1
MySQL thread id 211935715, query id 3146186169 [SERVER B] Updating

UPDATE images_unread_comments
    SET unread = 0
    WHERE user_id = 1 AND comment_id IN(1,2,3) AND unread = 1
    *** (2) HOLDS THE LOCK(S):
RECORD LOCKS space id 0 page no 404976 n bits 632 index users_unread_comments of table images_unread_comments trx id 1 2611184892 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;;

Record lock, heap no 555 PHYSICAL RECORD: n_fields 3; compact format; info bits 0
 0: len 4; hex 0001461a; asc   F ;; 1: len 1; hex 01; asc  ;; 2: len 6; hex 00000e67daf0; asc    g  ;;

Record lock, heap no 556 PHYSICAL RECORD: n_fields 3; compact format; info bits 0
 0: len 4; hex 0001461a; asc   F ;; 1: len 1; hex 01; asc  ;; 2: len 6; hex 00000e67dadb; asc    g  ;;

Record lock, heap no 557 PHYSICAL RECORD: n_fields 3; compact format; info bits 0
 0: len 4; hex 0001461a; asc   F ;; 1: len 1; hex 01; asc  ;; 2: len 6; hex 00000e67d940; asc    g @;;

Record lock, heap no 558 PHYSICAL RECORD: n_fields 3; compact format; info bits 32
 0: len 4; hex 0001461a; asc   F ;; 1: len 1; hex 01; asc  ;; 2: len 6; hex 00000e67d888; asc    g  ;;

*** (2) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 0 page no 404976 n bits 632 index users_unread_comments of table images_unread_comments trx id 1 2611184892 lock_mode X locks gap before rec insert intention waiting
Record lock, heap no 558 PHYSICAL RECORD: n_fields 3; compact format; info bits 32
 0: len 4; hex 0001461a; asc   F ;; 1: len 1; hex 01; asc  ;; 2: len 6; hex 00000e67d888; asc    g  ;;

*** WE ROLL BACK TRANSACTION (1)

我注意到的是两个SQL语句是相同的;然而，一个正在服务器A上执行，另一个正在服务器B上执行。无论发生什么原因 - 如果两个查询以相同的顺序锁定相同的密钥，为什么会造成死锁？或者我首先误解了死锁的错误？

Answer 1

似乎事务1执行了另一个操作（插入？），其中它锁定了索引中的间隙。它等待事务2执行更新，因为2已使用ID 1锁定记录。但事务2无法继续，因为事务1持有对索引的锁定。如果您可以通过此操作隔离事务中使用的所有SQL语句，我们可以看到死锁的确切原因

具有相同查询的死锁

1 个答案: