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。