一、rollback保存点的锁释放

在保存点后如果做了操作造成了行锁，是否rollback回来后还会保留操作时引起的行锁？

设计：在保存点后进行delete操作，查看rollback之前和之后的事务锁变化。

mysql> start transaction;

Query OK, 0 rows affected (0.00 sec)

mysql> savepoint a;

Query OK, 0 rows affected (0.00 sec)

mysql> select * from t5;   ###保存点状态

+------+------+

| id  | num  |

+------+------+

|   2 | aa   |

|   3 | c    |

+------+------+

2 rows in set (0.00 sec)

mysql> delete from t5 where id=2; ###更改操作

Query OK, 1 row affected (0.00 sec)

mysql> rollback to a;      ####回滚到保存点时

Query OK, 0 rows affected (0.00 sec)

mysql> select * from t5;  ###rollback后数据还原到事务保存点状态，即撤销delete操作

+------+------+

| id  | num  |

+------+------+

|   2 | aa   |

|   3 | c    |

+------+------+

2 rows in set (0.00 sec)

show engine innodb status;

rollback之前

------------

TRANSACTIONS

------------

Trx id counter 18044

Purge done for trx's n:o < 18041 undon:o < 0 state: running but idle

History list length 566

LIST OF TRANSACTIONS FOR EACH SESSION:

---TRANSACTION 18037, not started

MySQL thread id 272, OS thread handle0x7f61312b0700, query id 79768 localhost root init

show engine innodb status

---TRANSACTION 18039, ACTIVE 17 sec

2 lock struct(s), heap size 360, 3 rowlock(s), undo log entries 1 ###delete造成锁形成

MySQL thread id 274, OS thread handle0x7f60bd82d700, query id 79767 localhost root cleaning up

Trx read view will not see trx with id>= 18040, sees < 18040

Rollback之后

------------

TRANSACTIONS

------------

Trx id counter 18046

Purge done for trx's n:o < 18045 undon:o < 0 state: running but idle

History list length 567

LIST OF TRANSACTIONS FOR EACH SESSION:

---TRANSACTION 18037, not started

MySQL thread id 272, OS thread handle0x7f61312b0700, query id 79771 localhost root init

show engine innodb status

---TRANSACTION 18045, ACTIVE 5 sec

MySQL thread id 274, OS thread handle0x7f60bd82d700, query id 79770 localhost root cleaning up

Trx read view will not see trx with id>= 18046, sees < 18046

###锁已经被释放

结论：

Rollback释放了savepoint后delete操作的行锁。

二、回滚保存点只撤销本事务保存点后的操作

回滚保存点后，是否撤销了保存点后其他的事务对数据进行修改？

设计：设置保存点，事务二对no_index表进行update操作，然后回滚保存点，比较回滚前后数据变化。

set tx_isolation='read_committed';

事务一

mysql> start transaction ;

Query OK, 0 rows affected (0.00 sec)

mysql> savepoint modi;

Query OK, 0 rows affected (0.00 sec)

mysql> select * from no_index; ###事务二对no_index表操作前

+------+------+------+

| id  | fir  | sec  |

+------+------+------+

|   1 | aa   | bb   |

|   3 | b    | c    |

|   4 | c    | d    |

|   5 | e    | f    |

|   7 | e    | q    |

|   8 | cd   | qq   |

|  11 | a    | b    |

+------+------+------+

7 rows in set (0.00 sec)

mysql> select * from no_index;  ###事务二对no_index表操作后

+------+------+------+

| id  | fir  | sec  |

+------+------+------+

|   1 | aa   | b    |

|   3 | b    | c    |

|   4 | c    | d    |

|   5 | e    | f    |

|   7 | e    | q    |

|   8 | cd   | qq   |

|  11 | a    | b    |

+------+------+------+

7 rows in set (0.00 sec)

mysql> rollback to modi;

Query OK, 0 rows affected (0.00 sec)

mysql> select * from no_index; ####回滚到保存点后数据没有发生变化

+------+------+------+

| id  | fir  | sec  |

+------+------+------+

|   1 | aa   | b    |

|   3 | b    | c    |

|   4 | c    | d    |

|   5 | e    | f    |

|   7 | e    | q    |

|   8 | cd   | qq   |

|  11 | a    | b    |

+------+------+------+

7 rows in set (0.00 sec)

事务二

mysql> update no_index set sec='b' whereid='1'; ###对表进行update操作

Query OK, 1 row affected (0.01 sec)

Rows matched: 1  Changed: 1 Warnings: 0

mysql> rollback to modi;       ###可以看出保存点依附于事务中

ERROR 1305 (42000): SAVEPOINT modi does notexist

结论：

1.保存点回滚只是撤销本事务保存点后的操作，对保存点后其他事务的操作不凑效。

2.保存点的声明和定义只在本事务中凑效，而且当本事务commit或rollback后，保存点也不复存在。