MySQL如何找出未提交事务信息

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！