Why Am I Getting \'MySQLNonTransientConnectionException: No operations allowed after connection closed\' and How Can I Fix It?

Database Timeout and Connection Pooling Overload

This Hibernate issue, "com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed," arises when a persistent connection is implicitly closed due to inactivity.

Cause:

The connection is established but remains inactive for an extended period, exceeding the server's "wait_timeout" or the client timeout settings like "connectionTimeout".

Resolution:

1. Adjust Server and Client Timeouts:

• On the server side, increase the "wait_timeout" parameter in the MySQL configuration.
• On the client side, specify the "connectionTimeout" and "readTimeout" properties in your connection configuration.

2. Configure Connection Pooling:

• Use a third-party connection pool like C3P0 instead of Hibernate's built-in pool.
• Configure appropriate pool parameters such as "maxPoolSize," "minPoolSize," "idleTimeout," and "maxIdleTime."

Sample hibernate.cfg.xml Configuration Using C3P0:

<code class="xml"><property name="connection.provider_class">org.hibernate.connection.C3P0ConnectionProvider</property>
<property name="c3p0.max_size">20</property>
<property name="c3p0.min_size">5</property>
<property name="c3p0.timeout">1800</property>
<property name="c3p0.idleTestPeriod">3600</property>
<property name="c3p0.maxIdleTime">3600</property></code>

Additional Tips:

• Check any firewalls or proxy servers that might be blocking or timing out connections.
• Consider using a JDBC driver that supports JDBC Connection Pooling, like MySQL Connector/J.
• Monitor connection usage patterns and adjust pool sizes accordingly.

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