查找MySQL线程中死锁的ID的方法

 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。