Hi ,
I have a problem with Hibernate-MySQL appln in which database connection gets lost and is not recovering after some 5 hours of inactivity throwing, with following exception.


EXCEPTION
=========
Caused by: com.mysql.jdbc.CommunicationsException: Communications link failure due to underlying exception:

** BEGIN NESTED EXCEPTION **

java.net.UnknownHostException
MESSAGE: serverURL

STACKTRACE:

java.net.UnknownHostException: serverURL
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:153)
at java.net.Socket.connect(Socket.java:452)
at java.net.Socket.connect(Socket.java:402)
at java.net.Socket.<init>(Socket.java:309)
at java.net.Socket.<init>(Socket.java:124)
at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:130)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:265)
at com.mysql.jdbc.Connection.createNewIO(Connection.java:1682)
at com.mysql.jdbc.Connection.<init>(Connection.java:400)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:224)
at org.jboss.resource.adapter.jdbc.local.LocalManagedConnectionFactory


Any Idea why this happens only in Hibernate. I use same JDBC driver for other applications which work without causing this problem. Its only when used with Hibernate I get this error.

I saw few hints about this in MySQL forums, nothing worked for me. I will be grateful if anyone help me solve this.

Regards,
Aru K

This is because you use the default not for production connection pool that is enabled by default. Use C3P0 instead and your problem will be solved. If you're curious have a look at the source for the connection pool and from what I can remember it's just a simple infinity pool that doesn't validate stale/dead connections.

Hi Jamie,
Thanks for your reply.
Below is my configuration file which defines connection pool (using c3p0)

<hibernate-configuration>
<session-factory>
<!-- local connection properties -->

<property name="hibernate.connection.url">
jdbc:mysql://localhost:3306/rtttest
</property>
<property name="hibernate.connection.driver_class">
com.mysql.jdbc.Driver
</property>

<property name="hibernate.connection.username">arum</property>
<property name="hibernate.connection.password">priya</property>
<property name="hibernate.c3p0.min_size">5</property>
<property name="hibernate.c3p0.max_size">20</property>
<property name="hibernate.c3p0.timeout">30</property>
<property name="hibernate.c3p0.max_statements">50</property>


<!-- dialect for MySQL -->
<property name="dialect">
org.hibernate.dialect.MySQLDialect
</property>
<property name="hibernate.show_sql">true</property>
<property name="hibernate.use_outer_join">true</property>
<property name="hibernate.cglib.use_reflection_optimizer">false</property>
<property name="hibernate.use_sql_comments">true</property>
<mapping resource="cmmi.hbm.xml" />
</session-factory>
</hibernate-configuration>



Am I missing anything here? I do not get any exception when I use the application without any big break.

Your kind assistance is greatly appreciated.

Regards,
Aru K

Is the correct way of putting it in hibernate.cfg.xml

Note the lack of hibernate.

Hi ,
Even if I ignore hibernate prefix, it works without any problem. But dont know if this would solve the problem. Is there anyway to simulate the dead condition within 5 mins, instead of default 8 hours in MySQL???

Thanks in advance!!!