Hibernate JDBCConnectionException: could not execute query- Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException:

"org.quartz.JobExecutionException: could not execute query; nested exception is org.hibernate.exception.JDBCConnectionException: could not execute query [See nested exception: org.springframework.dao.DataAccessResourceFailureException: could not execute query; nested exception is org.hibernate.exception.JDBCConnectionException: could not execute query]
Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: The last packet successfully received from the server was 13,768,115 milliseconds ago.  The last packet sent successfully to the server was 13,768,115 milliseconds ago. is longer than the server configured value of 'wait_timeout'. You should consider either expiring and/or testing connection validity before use in your application, increasing the server configured values for client timeouts, or using the Connector/J connection property 'autoReconnect=true' to avoid this problem."

This problem occurred in a Grails application having a cron job that requests some data from an external server, processes it and persists some results. However the data is very large and the app requires 2+ Hrs. to process all of it before persisting a small result. The jdbc connection remains idle during this time.
Setting 'autoReconnect=true' or max_idle_time is certainly not a reliable solution for this.

What worked for me:
http://sacharya.com/grails-dbcp-stale-connections/: This was my exact problem. It says "By default, DBCP holds the pooled connections open for infinite time. But a database connection is essentially a socket connection, and it doesn’t come for free. The host OS, database host, and firewall have to allocate a certain amount of memory and other resources for each socket connection. It makes sense to those devices not to hold onto idle connections for ever. So the idea is to make sure that you don’t have stale connections in your pool that would otherwise be silently dropped by OS or firewall."

Modified my Datasource.groovy for working out this solution.
Had to use the following syntax from: http://stackoverflow.com/questions/376544/grails-mysql-maxpoolsize
Modified my Datasource.groovy:

dataSource {
    pooled = true
    dbCreate = "update"
    url = "jdbc:mysql://localhost/yourDB"
    driverClassName = "com.mysql.jdbc.Driver"
    username = "yourUser"
    password = "yourPassword"
    properties {
        maxActive = 50
        maxIdle = 25
        minIdle = 5
        initialSize = 5
        minEvictableIdleTimeMillis = 60000
        timeBetweenEvictionRunsMillis = 60000
        maxWait = 10000     
    }   }

Other relevant links:

http://drglennn.blogspot.com/2009/05/javasqlsqlexception-communication-link.html
http://commons.apache.org/dbcp/configuration.html
http://www.grails.org/DataSources+New
http://www.grails.org/1.2+Release+Notes