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 status\G   ------------ 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_TRX\G *************************** 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



mysql>  kill thread_id