There is case that does not close pooled connections

[mberta]

MyBatis version

3.4.1

Database vendor and version

MySQL Oracle community edition version 5.7.13

Test case or example project

https://github.com/mberta/mybatis-test-mysql-aborted-connection

Steps to reproduce

Run the example project

Expected result

Actual result

The example project executes a dummy SELECT 1 statement against a mysql server and it generates an error message in mysql server log like this:

2016-11-03T11:30:44.894384Z 2558213 [Note] Aborted connection 2558213 to db: 'COPERNICO' user: 'copernicodba' host: '10.242.1.26' (Got an error reading communication packets)

Don't know if this is an issue or not, but it seems to me that mybatis shouldn't generate an 'aborted connection' as it does in the example project I've attached.
I should add that changing datasource type from POOLED to UNPOOLED makes the problem disappear.

[kazuki43zoo]

@mberta Thanks for reporting !!

I've confirmed that does not close a pooled connection in this case.
The PooledDataSource close pooled connections at the finalize method. However in this case, the finalize method does not called. As result, pooled connections has been aborted during shutdown a JVM.

I will proposed a solution to prevent this issue as workaround.

Please close pooled connection calling the PooledDataSource#forceCloseAll method on your application shutdown phase as follow:

((PooledDataSource)sqlSessionFactory.getConfiguration().getEnvironment().getDataSource()).forceCloseAll();

We will consider a best solution to prevent this issue for next release.

[mberta]

@kazuki43zoo the problem seems not related to the shutdown of the JVM. In the snippet of code I've posted, if you call pingDb() method multiple times you should notice a message in mysql server log for every call of the pingDb() method.

[kazuki43zoo]

Hi @mberta,

Sorry, i don't understand your comment.
In my understanding, your application should be closed pooled connections before shutdown of the JVM. However, current implementation of the PooledDataSource does not close pooled connections automatically. I think this implementation is root cause of this issue.

I think this issue can be prevented adding following code (This solution is workaround):

    private void pingDb() throws IOException {
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();

        try (SqlSession session = sqlSessionFactory.openSession()) {
            Mapper mapper = session.getMapper(TestMySqlAbortedConnection.Mapper.class);
            mapper.pingDb();
        } finally {
            // Add following code
            ((PooledDataSource)sqlSessionFactory.getConfiguration().getEnvironment().getDataSource()).forceCloseAll();
        }


    }

or

    private SqlSessionFactory getSqlSessionFactory() throws IOException {
        InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
        SqlSessionFactory sqlSessionFactory =
                new SqlSessionFactoryBuilder().build(inputStream, System.getProperties());

        Configuration configuration = sqlSessionFactory.getConfiguration();
        configuration.addMapper(Mapper.class);

        // Add following code
        Runtime.getRuntime().addShutdownHook(new Thread() {
            @Override
            public void run() {
                ((PooledDataSource)sqlSessionFactory.getConfiguration().getEnvironment().getDataSource()).forceCloseAll();
            }
        });

        return sqlSessionFactory;
    }

[mberta]

@kazuki43zoo, you're perfectly right! I was misunderstanding your answer

[Quantas]

@kazuki43zoo does this bug affect more than just 3.4.1?

[kazuki43zoo]

@Quantas Probably yes, this issue affect all versions.

[awxiaoxian2020]

Hi, @kazuki43zoo is the bug fixed?