解决 MYSQL 8 小时问题

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最近的一个项目在Hibernate使用C3P0的连接池，数据库为Mysql。开发测试没有问题，在运行中每个一段长的空闲时间就出现异常: java 代码
1. org.hibernate.exception.JDBCConnectionException: could not execute query  2. at
org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:74)  3. at
org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)  4. .......  5. Caused by:
com.mysql.jdbc.exceptions.MySQLNonTransientConnectionException: No operations allowed after connection closed.Connection was implicitly closed due to underlying exception/error:  6. ** BEGIN NESTED EXCEPTION **
7. com.mysql.jdbc.CommunicationsException
8. MESSAGE: Communications link failure due to underlying exception:  9. ** BEGIN NESTED EXCEPTION **  10.java.net.SocketException  11.MESSAGE: Broken pipe  12.STACKTRACE:
13.java.net.SocketException: Broken pipe
14.at java.net.SocketOutputStream.socketWrite0(Native Method)  15.......
16.** END NESTED EXCEPTION **

查看了Mysql的文档，以及Connector/J的文档以及在线说明发现，出现这种异常的原因是：
Mysql服务器默认的“wait_timeout”是8小时，也就是说一个connection空闲超过8个小时，Mysql将自动断开该 connection。这就是问题的所在，在C3P0 pools中的connections如果空闲超过8小时，Mysql将其断开，而C3P0并不知道该connection已经失效，如果这时有 Client请求connection，C3P0将该失效的Connection提供给Client，将会造成上面的异常。解决的方法有3种：
1. 增加wait_timeout的时间。
2. 减少Connection pools中connection的lifetime。  3. 测试Connection pools中connection的有效性。
当然最好的办法是同时综合使用上述3种方法，下面就DBCP和C3P0分别做一说明，假设wait_timeout为默认的8小时
C3P0增加以下配置信息:

1. //获取connnection时测试是否有效

testConnectionOnCheckin = true

2. //自动测试的table名称

automaticTestTable=C3P0TestTable

3. //set to something much less than wait_timeout, prevents connections from going stale

idleConnectionTestPeriod = 18000

4. //set to something slightly less than wait_timeout, preventing 'stale' connections from being handed out

maxIdleTime = 25000

5. //if you can take the performance 'hit', set to "true"

testConnectionOnCheckout = true

更多的配置信息大家可以查看C3P0文档，Connector/J文档，以及DBCP的文档。转: http://www.javaeye.com/article/38506 我自己的配置:
jdbc.driverClass=com.mysql.jdbc.Driver
jdbc.jdbcUrl = jdbc:mysql://localhost:3306/test jdbc.user = root
jdbc.password = 12345 jdbc.miniPoolSize = 1 jdbc.maxPoolSize = 20 jdbc.initialPoolSize = 1 jdbc.maxIdleTime = 25000 jdbc.acquireIncrement = 1
jdbc.acquireRetryAttempts = 30 jdbc.acquireRetryDelay = 1000
jdbc.testConnectionOnCheckin = true jdbc.automaticTestTable = c3p0TestTable jdbc.idleConnectionTestPeriod = 18000 jdbc.checkoutTimeout=3000
<bean id="dataSource"
class="com.mchange.v2.c3p0.ComboPooledDataSource" destroy-method="close">
   <property name="driverClass" value="${jdbc.driverClass}" />    <property name="jdbcUrl" value="${jdbc.jdbcUrl}" />    <property name="user" value="${jdbc.user}" />
   <property name="password" value="${jdbc.password}" />
   <property name="minPoolSize" value="${jdbc.miniPoolSize}" />    <property name="maxPoolSize" value="${jdbc.maxPoolSize}"/>
   <property name="initialPoolSize" value="${jdbc.initialPoolSize}"/>    <property name="maxIdleTime" value="${jdbc.maxIdleTime}"/>    <property name="acquireIncrement" value="${jdbc.acquireIncrement}"/>
   <property name="acquireRetryAttempts" value="${jdbc.acquireRetryAttempts}"/>    <property name="acquireRetryDelay" value="${jdbc.acquireRetryDelay}"/>
   <property name="testConnectionOnCheckin" value="${jdbc.testConnectionOnCheckin}"/>    <property name="automaticTestTable" value="${jdbc.automaticTestTable}"/>
   <property name="idleConnectionTestPeriod" value="${jdbc.idleConnectionTestPeriod}"/>
   <property name="checkoutTimeout" value="${jdbc.checkoutTimeout}"/>
</bean>

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