時間が経つとMySQLの接続エラーが出る

Matsumoto.JS - Grails: 時間が経つとMySQLの接続エラーが出る
なるほど

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: The last packet successfully received from the server was 152,741,137 milliseconds ago.
The last packet sent successfully to the server was 152,741,141 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.

ってでて何かと思った