MySQL 事务可以在没有 ROLLBACK 查询的情况下回滚吗？

Question

I'm working on a financial system and I've got a problem with the MySQL transactions.

The system is a simple stock exchange, where users can buy and sell virtual shares. To keep integrity in buy and sell process I use transactions. The problem is that in some cases (I don't know what it depends on) some of transactions are rolled back (or not commited), but next queries are processed.

The process is following:

1. User wants to buy shares for 1000 USD
2. In orderbook there are 4 offers for 250 USD
3. START TRANSACTION
4. For every offer:
5. Script does a UPDATE query (moving USD from one user to another and shares in the opposite way). Then script INSERTs entries to history tables.
6. Users pay a fee (UPDATE balances).
7. Repeat 5 and 6 for the next offer.
8. COMMIT

Now the key part - in some cases changes from point 5 are not saved, but from the 6 they are (I see that fee was paid, but there is no transaction in the history). I'm not using ROLLBACK during this transactions and the script is not breaking (because in this case fee wouldn't be paid).

Is there any possibility that transaction is rolling back without ROLLBACK query? Or can MySQL COMMIT only few newest queries instead of all?

Answer 1

Transactions or not, it's the responsibility of your client code to verity that all your INSERT or UPDATE queries complete successfully and then either issue a explicit ROLLBACK or close the connection withour COMMIT to issue an implicity ROLLBACK. If any of them fails but your code goes on, those queries will not take effect (because they failed) but the rest will do.

Here's a simplified example:

mysql> create table test (
    ->     id int(10) unsigned not null,
    ->     primary key (id)
    -> );
Query OK, 0 rows affected (0.02 sec)

mysql> insert into test(id) values (1);
Query OK, 1 row affected (0.00 sec)

mysql> start transaction;
Query OK, 0 rows affected (0.00 sec)

mysql> insert into test(id) values (2);
Query OK, 1 row affected (0.00 sec)

mysql> insert into test(id) values (-3);
ERROR 1264 (22003): Out of range value for column 'id' at row 1

We should have rollbacked and aborted here, but we didn't.

mysql> insert into test(id) values (4);
Query OK, 1 row affected (0.00 sec)

mysql> commit;
Query OK, 0 rows affected (0.00 sec)

mysql> select * from test;
+----+
| id |
+----+
|  1 |
|  2 |
|  4 |
+----+
3 rows in set (0.00 sec)

4 rows expected, got 3.

Other than that, there're many circumstances where you can get an unwanted COMMIT but an unwanted ROLLBACK is something I'm not sure that can happen unless you terminate a session with pending changes.

Answer 2

It's long time since the question was asked, but the problem actually was that I didn't check for the SQL errors for every query.

Actually at some points, when I should rollback transaction, I didn't do it.

If your are looking for answer - check again if you testing ALL queries in your transaction for successful execution and don't trust that the framework you are using is doing it for you automatically (just check it again).