前陣子，我寫了一篇博客“ORACLE中能否找到未提交事務的SQL語句”， 那么在MySQL數據庫中，我們能否找出未提交事務執行的SQL語句或未提交事務的相關信息呢？
實驗驗證了一下，如果一個會話(連接)里面有一個未提交事務，然后不做任何操作，那么這個線程處於Sleep狀態
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>
在另外一個會話（連接）里面，查詢這個超過10秒未提交事務的詳細信息：
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
如上截圖所示，trx_query 為NULL值。基本上無法找到未提交事務的SQL語句，MySQL內部關於事務的信息不是很細，甚至可以說有點簡潔。我甚至無法定位到在那個表上發生了鎖。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
如果未提交的事務，阻塞了其它會話，那么有可能（僅僅是存在可能性，很多場景也不能找到位提交事務的相關SQL）找到未提交事務執行的SQL
如下測試所示，會話（連接 connection_id=11）中執行了delete操作，但是未提交事務
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>
另外一個會話（連接）執行了一個更新記錄的操作。此時SQL將被阻塞。
mysql> select connection_id();
+-----------------+
| connection_id() |
+-----------------+
| 13 |
+-----------------+
1 row in set (0.00 sec)
mysql>
mysql> update kkk set id=100 where id=1;
我們在另外的會話中，執行下面SQL就可以查到未提交事務最后執行的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>
總結：基本上MySQL只能找到未提交事務的基本信息，例如trx_mysql_thread_id等。某些場景下，我們幾乎沒有方法找出未提交事務執行的SQL等詳細信息。搞不清未提交事務做了什么操作！