Communications Link Failure ClearDB

Question

I realize that there are other questions similar to mine but I feel mine is a bit different so I'm going to ask it anyway. I've been using hibernate to develop a java web application and have run in to no problems when I run it on a localhost Tomcat server. I've, however, been running into problems after trying to deploy it on Heroku and using the free version of ClearDB as the website would randomly throw an exception. Specifically, I am getting a

org.hibernate.exception.JDBCConnectionException: Communications link failure 

Things I've found on google but believe to not be my issue:

• Database was idle for too long ( > 8hours). I've been continuously using the website so it definitely has not been idle for longer than 8 hours.
• Too many connections to Database. I'm the only one currently connected to the database and the website says there is a maximum of 10 connections so I'm within their limit

My configuration file

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
    <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
    <property name="hibernate.connection.password">PASSWORD</property>
    <property name="hibernate.connection.url">jdbc:mysql://DBURL?reconnect=true</property>
    <property name="hibernate.connection.username">USERNAME</property>
    <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
    <property name= "hbm2ddl.auto">update</property>
    <property name="show_sql">true</property>
</session-factory>

Thanks in advance

Answer 1

I'd be willing to bet that this goes away if you use JawsDB add-on instead of ClearDB:

$ heroku addons:destroy cleardb
$ heroku addons:create jawsdb:kitefin

I have so many problems with ClearDB.

If you must use ClearDB, I recommend adding a connectionTestQuery to your database connection pool configuration. I'm not sure how to do this generically, but if you are using HikariCP (which is great and you should use), you can add something like:

<property name="hibernate.hikari.connectionTestQuery">SELECT 1</property>

Answer 2

ClearDB routinely closes connections with idle/sleep status for more than 60 seconds. This happens when your system think it has a DB connection but the remote host has closed it. As the previous respondent mentioned, a quick connectionTestQuery should resolve this.