InnoDB INFORMATION_SCHEMA 里有三张表可以用来监控和诊断锁的问题。

INNODB_TRX
包含正在InnoDB里执行的每个事务的相关信息，包括事务是否在等待锁，事务的开始时间和事务正在执行的SQL语句。

INNODB_LOCKS
记录InnoDB里每个正在等待另一个事务释放锁(INNODB_TRX.TRX_STATE='LOCK WAIT')的事务的相关信息，这些事务被“blocking lock request”事件阻塞，这些锁的请求为被另一个事务占用的行锁或表锁。
等待或阻塞的事务不能进行，直到占有锁的事务提交或回滚。这张表记录事务请求的锁，占有锁的事务信息，占有锁的事务的状态('RUNNING', 'LOCK WAIT', 'ROLLING BACK' or 'COMMITTING')，占有锁的模式(read vs. write, shared vs. exclusive)。

INNODB_LOCK_WAITS
记录哪些事务在等待锁以及等待的锁的类型，REQUESTED_LOCK_ID代表事务请求的锁的ID，BLOCKING_LOCK_ID代表占有锁的ID。

事务1
mysql> BEGIN;
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT MSISDN FROM t50 FOR UPDATE;
+----------------+
| MSISDN         |
+----------------+
| +3301000000011 |
| +3301000000013 |
| +3301000000015 |
| +3301000000015 |
| +3301000000017 |
| +3301000000019 |
+----------------+
6 rows in set (0.00 sec)

mysql> SELECT SLEEP(1000);

事务2
mysql> SELECT IMEI FROM t50 FOR UPDATE;

事务3
mysql> SELECT IMSI FROM t50 FOR UPDATE;

再开一个会话，查看线程信息
mysql> show processlist;
+----+------+-----------+------+---------+------+--------------+---------------------------------+-----------+---------------+
| Id | User | Host      | db   | Command | Time | State        | Info                            | Rows_sent | Rows_examined |
+----+------+-----------+------+---------+------+--------------+---------------------------------+-----------+---------------+
| 70 | root | localhost | test | Query   |    8 | Sending data | SELECT IMEI FROM t50 FOR UPDATE |         0 |             0 |
| 71 | root | localhost | test | Query   | 310 | User sleep   | SELECT SLEEP(1000)              |         0 |             0 |
| 72 | root | localhost | test | Query   |    6 | Sending data | SELECT IMSI FROM t50 FOR UPDATE |         0 |             0 |
| 73 | root | localhost | test | Query   |    0 | init         | show processlist                |         0 |             0 |
+----+------+-----------+------+---------+------+--------------+---------------------------------+-----------+---------------+
4 rows in set (0.03 sec)

查看锁的信息
mysql> SELECT r.trx_id waiting_trx_id,
    ->        r.trx_mysql_thread_id waiting_thread,
    ->        r.trx_query waiting_query,
    ->        b.trx_id blocking_trx_id,
    ->        b.trx_mysql_thread_id blocking_thread,
    ->        b.trx_query blocking_query
    ->    FROM       information_schema.innodb_lock_waits w
    ->    INNER JOIN information_schema.innodb_trx b ON
    ->     b.trx_id = w.blocking_trx_id
    ->   INNER JOIN information_schema.innodb_trx r ON
    ->     r.trx_id = w.requesting_trx_id;
+----------------+----------------+---------------------------------+-----------------+-----------------+---------------------------------+
| waiting_trx_id | waiting_thread | waiting_query                   | blocking_trx_id | blocking_thread | blocking_query                  |
+----------------+----------------+---------------------------------+-----------------+-----------------+---------------------------------+
| 6288648        |             72 | SELECT IMSI FROM t50 FOR UPDATE | 6288647         |              70 | SELECT IMEI FROM t50 FOR UPDATE |
| 6288648        |             72 | SELECT IMSI FROM t50 FOR UPDATE | 6288638         |              71 | SELECT SLEEP(1000)              |
| 6288647        |             70 | SELECT IMEI FROM t50 FOR UPDATE | 6288638         |              71 | SELECT SLEEP(1000)              |
+----------------+----------------+---------------------------------+-----------------+-----------------+---------------------------------+
3 rows in set (0.00 sec)

可以看到，最初执行SQL的线程是 71，线程 70 等待线程 71 ，线程 72 在等待线程 70、71

mysql> select * from information_schema.INNODB_LOCKS;
+----------------+-------------+-----------+-----------+--------------+-----------------+------------+-----------+----------+----------------+
| lock_id        | lock_trx_id | lock_mode | lock_type | lock_table   | lock_index      | lock_space | lock_page | lock_rec | lock_data      |
+----------------+-------------+-----------+-----------+--------------+-----------------+------------+-----------+----------+----------------+
| 6288651:78:3:2 | 6288651     | X         | RECORD    | `test`.`t50` | GEN_CLUST_INDEX |         78 |         3 |        2 | 0x000000000607 |
| 6288650:78:3:2 | 6288650     | X         | RECORD    | `test`.`t50` | GEN_CLUST_INDEX |         78 |         3 |        2 | 0x000000000607 |
| 6288638:78:3:2 | 6288638     | X         | RECORD    | `test`.`t50` | GEN_CLUST_INDEX |         78 |         3 |        2 | 0x000000000607 |
+----------------+-------------+-----------+-----------+--------------+-----------------+------------+-----------+----------+----------------+
3 rows in set (0.00 sec)

mysql> select trx_id,trx_state,trx_started,trx_requested_lock_id,trx_wait_started,trx_mysql_thread_id,trx_query from information_schema.INNODB_TRX;
+---------+-----------+---------------------+-----------------------+---------------------+---------------------+---------------------------------+
| trx_id | trx_state | trx_started         | trx_requested_lock_id | trx_wait_started    | trx_mysql_thread_id | trx_query                       |
+---------+-----------+---------------------+-----------------------+---------------------+---------------------+---------------------------------+
| 6288669 | LOCK WAIT | 2016-09-05 14:14:28 | 6288669:78:3:2        | 2016-09-05 14:14:28 |                  72 | SELECT IMSI FROM t50 FOR UPDATE |
| 6288668 | LOCK WAIT | 2016-09-05 14:14:26 | 6288668:78:3:2        | 2016-09-05 14:14:26 |                  70 | SELECT IMEI FROM t50 FOR UPDATE |
| 6288638 | RUNNING   | 2016-09-05 11:41:59 | NULL                  | NULL                |                  71 | SELECT SLEEP(1000)              |
+---------+-----------+---------------------+-----------------------+---------------------+---------------------+---------------------------------+
3 rows in set (0.00 sec)

mysql> select * from information_schema.INNODB_LOCK_WAITS;
+-------------------+-------------------+-----------------+------------------+
| requesting_trx_id | requested_lock_id | blocking_trx_id | blocking_lock_id |
+-------------------+-------------------+-----------------+------------------+
| 6288671           | 6288671:78:3:2    | 6288670         | 6288670:78:3:2   |
| 6288671           | 6288671:78:3:2    | 6288638         | 6288638:78:3:2   |
| 6288670           | 6288670:78:3:2    | 6288638         | 6288638:78:3:2   |
+-------------------+-------------------+-----------------+------------------+
3 rows in set (0.00 sec)

检查Innodb_row_lock状态变量来分析系统上的行锁的争夺情况
mysql> show global status like '%innodb%row%lock%';
+-------------------------------+-------+
| Variable_name                 | Value |
+-------------------------------+-------+
| Innodb_row_lock_current_waits | 0     |
| Innodb_current_row_locks      | 0     |
| Innodb_row_lock_time          | 0     |
| Innodb_row_lock_time_avg      | 0     |
| Innodb_row_lock_time_max      | 0     |
| Innodb_row_lock_waits         | 0     |
+-------------------------------+-------+
6 rows in set (0.00 sec)

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MySQL 5.7 查询InnoDB锁表

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