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 org.hibernate.exception.JDBCConnectionException: could not execute query at org.hibernate.exception.SQLStateConve
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
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org.hibernate.exception.JDBCConnectionException: could not execute query
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at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:74)
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at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)
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.......
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Caused by: com.mysql.jdbc.exceptions.MySQLNonTransientConnectionException: No operations allowed after connection closed.Connection was implicitly closed due to underlying exception/error:
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** BEGIN NESTED EXCEPTION **
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com.mysql.jdbc.CommunicationsException
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MESSAGE: Communications link failure due to underlying exception:
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** BEGIN NESTED EXCEPTION **
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java.net.SocketException
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MESSAGE: Broken pipe
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STACKTRACE:
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java.net.SocketException: Broken pipe
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at java.net.SocketOutputStream.socketWrite0(Native Method)
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......
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** 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:
- 增加wait_timeout的时间。
- 减少Connection pools中connection的lifetime。
- 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
DBCP增加以下配置信息:
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//set to 'SELECT 1'
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validationQuery = "SELECT 1"
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//set to 'true'
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testWhileIdle = "true"
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//some positive integer
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timeBetweenEvictionRunsMillis = 3600000
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//set to something smaller than 'wait_timeout'
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minEvictableIdleTimeMillis = 18000000
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//if you don't mind a hit for every getConnection(), set to "true"
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testOnBorrow = "true"
C3P0增加以下配置信息:
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//获取connnection时测试是否有效
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testConnectionOnCheckin = true
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//自动测试的table名称
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automaticTestTable=C3P0TestTable
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//set to something much less than wait_timeout, prevents connections from going stale
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idleConnectionTestPeriod = 18000
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//set to something slightly less than wait_timeout, preventing 'stale' connections from being handed out
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maxIdleTime = 25000
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//if you can take the performance 'hit', set to "true"
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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。