Connection drop by DB - mysql

Question

I have a system with approximately 20 TPS. This system establishes DB connections to get some data. I am using Hibernate with c3p0 to manage my connections and Guice to ensure transactionality using the #transactional annotation.
Near about 0.3% of the request are failing because of some DB connection issue.
This is what the stack trace looks like.
javax.persistence.PersistenceException: org.hibernate.exception.JDBCConnectionException: could not prepare statement
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Caused by: org.hibernate.exception.JDBCConnectionException: could not prepare statement
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Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed
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Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
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Caused by: java.net.SocketException: Connection reset
My hibernate c3p0 settings are:
hibernate.connection.url = "jdbc:mysql://dbHost.com:3306/DB";
hibernate.dialect = "org.hibernate.dialect.MySQLDialect";
hibernate.cache.provider_class = "org.hibernate.cache.NoCacheProvider";
hibernate.hbm2ddl.auto = "update";
hibernate.show_sql = "false";
hibernate.connection.provider_class = "org.hibernate.c3p0.internal.C3P0ConnectionProvider";
hibernate.c3p0.min_size = "100";
hibernate.c3p0.max_size = "100";
hibernate.c3p0.idle_test_period = "100";
hibernate.c3p0.max_statements = "0";
hibernate.c3p0.timeout = "86400";
hibernate.c3p0.preferredTestQuery = "select 1";
My DB system variable:
connect_timeout=10
wait_timeout=86500
interactive_timeout=28800
These errors occur randomly, and when it is retried for the same input for which it initially failed it works.
What am I doing wrong?

Answer 1

Probably the easiest way to (hopefully!) address this is to add...
hibernate.c3p0.testConnectionOnCheckout = "true"
With your preferredTestQuery set, it's unlikely to be a performance problem. See here for some advice on Connection testing.