如果遇到死锁了，怎么解决呢？找到原始的锁ID，然后KILL掉一直持有的那个线程就可以了， 但是众多线程，可怎么找到引起死锁的线程ID呢？ MySQL 发展到现在，已经非常强大了，这个问题很好解决。 直接从数据字典连查找。

我们来演示下。

线程A，我们用来锁定某些记录，假设这个线程一直没提交，或者忘掉提交了。 那么就一直存在，但是数据里面显示的只是SLEEP状态。

mysql> set @@autocommit=0; Query OK, 0 rows affected (0.00 sec) mysql> use test; Reading table information for completion of table and column names You can turn off this feature to get a quicker startup with -A Database changed mysql> show tables; +—————-+ | Tables_in_test | +—————-+ | demo_test | | t3 | +—————-+ 2 rows in set (0.00 sec) mysql> select * from t3; +—-+——–+——–+————+—-+—-+—-+ | id | fname | lname | birthday | c1 | c2 | c3 | +—-+——–+——–+————+—-+—-+—-+ | 19 | lily19 | lucy19 | 2013-04-18 | 19 | 0 | 0 | | 20 | lily20 | lucy20 | 2013-03-13 | 20 | 0 | 0 | +—-+——–+——–+————+—-+—-+—-+ 2 rows in set (0.00 sec) mysql> update t3 set birthday = '2022-02-23' where id = 19; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> select connection_id(); +—————–+ | connection_id() | +—————–+ | 16 | +—————–+ 1 row in set (0.00 sec) mysql>

线程B， 我们用来进行普通的更新，但是遇到问题了，此时不知道是哪个线程把这行记录给锁定了？

mysql> use test; Reading table information for completion of table and column names You can turn off this feature to get a quicker startup with -A Database changed mysql> select @@autocommit; +————–+ | @@autocommit | +————–+ | 1 | +————–+ 1 row in set (0.00 sec) mysql> update t3 set birthday='2018-01-03' where id = 19; ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction mysql> select connection_id(); +—————–+ | connection_id() | +—————–+ | 17 | +—————–+ 1 row in set (0.00 sec) mysql> show processlist; +—-+——+———–+——+———+——+——-+——————+ | Id | User | Host | db | Command | Time | State | Info | +—-+——+———–+——+———+——+——-+——————+ | 10 | root | localhost | NULL | Sleep | 1540 | | NULL | | 11 | root | localhost | NULL | Sleep | 722 | | NULL | | 16 | root | localhost | test | Sleep | 424 | | NULL | | 17 | root | localhost | test | Query | 0 | init | show processlist | | 18 | root | localhost | NULL | Sleep | 5 | | NULL | +—-+——+———–+——+———+——+——-+——————+ 5 rows in set (0.00 sec) mysql> show engine innodb statusG ———— TRANSACTIONS ———— Trx id counter 189327 Purge done for trx's n:o < 189323 undo n:o < 0 state: running but idle History list length 343 LIST OF TRANSACTIONS FOR EACH SESSION: —TRANSACTION 0, not started MySQL thread id 11, OS thread handle 0x7f70a0c98700, query id 994 localhost root init show engine innodb status —TRANSACTION 189326, ACTIVE 2 sec starting index read mysql tables in use 1, locked 1 LOCK WAIT 2 lock struct(s), heap size 376, 1 row lock(s) MySQL thread id 17, OS thread handle 0x7f70a0bd5700, query id 993 localhost root updating update t3 set birthday='2018-01-03' where id = 19 ——- TRX HAS BEEN WAITING 2 SEC FOR THIS LOCK TO BE GRANTED: RECORD LOCKS space id 529 page no 3 n bits 72 index `PRIMARY` of table `test`.`t3` trx id 189326 lock_mode X waiting Record lock, heap no 2 PHYSICAL RECORD: n_fields 9; compact format; info bits 0 0: len 2; hex 3139; asc 19;; 1: len 6; hex 00000002e38c; asc ;; 2: len 7; hex 7e00000d2827c9; asc ~ (' ;; 3: len 6; hex 6c696c793139; asc lily19;; 4: len 6; hex 6c7563793139; asc lucy19;; 5: len 3; hex 8fcc57; asc W;; 6: len 4; hex 80000013; asc ;; 7: len 4; hex 80000000; asc ;; 8: len 4; hex 80000000; asc ;; —————— —TRANSACTION 189324, ACTIVE 641 sec 2 lock struct(s), heap size 376, 3 row lock(s), undo log entries 1 MySQL thread id 16, OS thread handle 0x7f70a0b94700, query id 985 localhost root cleaning up Trx read view will not see trx with id >= 189325, sees < 189325

上面的信息很繁多，也看不清楚到底哪里是哪里。

不过现在，我们只要从数据字典里面拿出来这部分信息就OK了。

mysql> SELECT * FROM information_schema.INNODB_TRXG *************************** 1. row *************************** trx_id: 189324 trx_state: RUNNING trx_started: 2013-04-18 17:48:14 trx_requested_lock_id: NULL trx_wait_started: NULL trx_weight: 3 trx_mysql_thread_id: 16 trx_query: NULL trx_operation_state: NULL trx_tables_in_use: 0 trx_tables_locked: 0 trx_lock_structs: 2 trx_lock_memory_bytes: 376 trx_rows_locked: 3 trx_rows_modified: 1 trx_concurrency_tickets: 0 trx_isolation_level: REPEATABLE READ trx_unique_checks: 1 trx_foreign_key_checks: 1 trx_last_foreign_key_error: NULL trx_adaptive_hash_latched: 0 trx_adaptive_hash_timeout: 10000 trx_is_read_only: 0 trx_autocommit_non_locking: 0 1 row in set (0.01 sec) mysql>

原来是线程16忘掉COMMIT了。