MySQL找出未提交事务信息的方法分享

前阵子，我写了一篇博客“ORACLE中能否找到未提交事务的SQL语句”， 那么在MySQL数据库中，我们能否找出未提交事务执行的SQL语句或未提交事务的相关信息呢？

实验验证了一下，如果一个会话(连接)里面有一个未提交事务，然后不做任何操作，那么这个线程处于Sleep状态

mysql> select connection_id() from dual;
+-----------------+
| connection_id() |
+-----------------+
|  6 |
+-----------------+
1 row in set (0.00 sec)

mysql> set session autocommit=0;
Query OK, 0 rows affected (0.00 sec)

mysql> delete from kkk where id =1;
Query OK, 1 row affected (0.00 sec)

mysql> 

在另外一个会话（连接）里面，查询这个超过10秒未提交事务的详细信息：

SELECT t.trx_mysql_thread_id
 ,t.trx_state
 ,t.trx_tables_in_use
 ,t.trx_tables_locked
 ,t.trx_query
 ,t.trx_rows_locked
 ,t.trx_rows_modified
 ,t.trx_lock_structs
 ,t.trx_started
 ,t.trx_isolation_level
 ,p.time
 ,p.user
 ,p.host
 ,p.db
 ,p.command
FROM information_schema.innodb_trx t
 INNER JOIN information_schema.processlist p
  ON t.trx_mysql_thread_id = p.id
WHERE t.trx_state = 'RUNNING'
 AND p.time > 10
 AND p.command = 'Sleep'\G 

如上截图所示，trx_query 为NULL值。基本上无法找到未提交事务的SQL语句，MySQL内部关于事务的信息不是很细，甚至可以说有点简洁。我甚至无法定位到在那个表上发生了锁。只能看到trx_row_locked、trx_row_modified、trx_started等信息。使用show engine innodb status也是如此，只能看到一些基本信息

mysql> show engine innodb status;

---TRANSACTION 1282583, ACTIVE 11937 sec

2 lock struct(s), heap size 360, 8 row lock(s), undo log entries 1

MySQL thread id 6, OS thread handle 0x7f8da2de3700, query id 190 localhost root

如果未提交的事务，阻塞了其它会话，那么有可能（仅仅是存在可能性，很多场景也不能找到位提交事务的相关SQL）找到未提交事务执行的SQL

如下测试所示，会话（连接 connection_id=11）中执行了delete操作，但是未提交事务

mysql> set session autocommit=0;
Query OK, 0 rows affected (0.00 sec)

mysql> select connection_id();
+-----------------+
| connection_id() |
+-----------------+
|  11 |
+-----------------+
1 row in set (0.01 sec)

mysql> delete from kkk where id=1;
Query OK, 1 row affected (0.00 sec)

mysql> 

另外一个会话（连接）执行了一个更新记录的操作。此时SQL将被阻塞。

mysql> select connection_id();
+-----------------+
| connection_id() |
+-----------------+
|  13 |
+-----------------+
1 row in set (0.00 sec)

mysql>
mysql> update kkk set id=100 where id=1;

我们在另外的会话中，执行下面SQL就可以查到未提交事务最后执行的SQL。

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 |
+----------------+----------------+----------------------------------+-----------------+-----------------+----------------+
| 2830  |  13 | update kkk set id=100 where id=1 | 2825  |  11 | NULL  |
+----------------+----------------+----------------------------------+-----------------+-----------------+----------------+
1 row in set (0.00 sec)

mysql> SELECT a.sql_text,
 -> c.id,
 -> d.trx_started
 -> FROM performance_schema.events_statements_current a
 -> join performance_schema.threads b
 ->  ON a.thread_id = b.thread_id
 -> join information_schema.processlist c
 ->  ON b.processlist_id = c.id
 -> join information_schema.innodb_trx d
 ->  ON c.id = d.trx_mysql_thread_id
 -> where c.id=11
 -> ORDER BY d.trx_started\G;
*************************** 1. row ***************************
 sql_text: delete from kkk where id =1
  id: 11
trx_started: 2019-06-12 23:36:13
1 row in set (0.03 sec)

ERROR:
No query specified

mysql> 

总结：

基本上MySQL只能找到未提交事务的基本信息，例如trx_mysql_thread_id等。某些场景下，我们几乎没有方法找出未提交事务执行的SQL等详细信息。搞不清未提交事务做了什么操作！

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