MySQL/Hibernate randomly has "Communications link failure"

Question

We have a webapp running Hibernate/C3PO 4.1.4.Final, Jetty, Java 6, and Mysql 5.1.63.

javax.persistence.PersistenceException: org.hibernate.exception.JDBCConnectionException: Communications link failure

The last packet successfully received from the server was 238,519 milliseconds ago. The last packet sent successfully to the server was 0 milliseconds ago.

Our persistence.xml's properties section looks like this...

  <properties>
        <property name="hibernate.show_sql" value="false"/>
        <!--Begin Credentials -->
        <property name="hibernate.connection.url"
                  value="${rp.config.db.url}&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
        <property name="hibernate.connection.username" value="${rp.config.db.user}"/>
        <property name="hibernate.connection.password" value="${rp.config.db.password}"/>
        <!--End Credentials -->
        <property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver"/>
        <property name="hibernate.dialect" value="com.printlogix.rp.server.utils.Mysql5BitBooleanDialect"/>
        <property name="hibernate.hbm2ddl.auto" value="validate"/>
        <!--C3PO -->
        <property name="hibernate.connection.provider_class"
                  value="org.hibernate.service.jdbc.connections.internal.C3P0ConnectionProvider"/>
        <property name="hibernate.c3p0.acquire_increment" value="25"/>
        <property name="hibernate.c3p0.idle_test_period" value="60"/>
        <property name="hibernate.c3p0.timeout" value="120"/>
        <property name="hibernate.c3p0.max_size" value="150"/>
        <property name="hibernate.c3p0.min_size" value="25"/>
        <property name="hibernate.c3p0.max_statement" value="0"/>
        <property name="hibernate.c3p0.preferredTestQuery" value="select 1;"/>

    </properties>

Our timeout on MySQL is set to 600 seconds. We have no idea how this is happening 1/5 times. The server has very little load, the database is relatively small, the servlets all run within seconds.

Anybody have any ideas?

Answer 1

This article explains the fix. C3P0 does not reconnect when a connection is expired.

http://www.databasesandlife.com/automatic-reconnect-from-hibernate-to-mysql/

It seems completely insane that the developers at Hibernate would not document this better.