转：
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:
- org.hibernate.exception.jdbcconnectionexception: could not execute query
- at org.hibernate.exception.sqlstateconverter.convert(sqlstateconverter.java:74)
- at org.hibernate.exception.jdbcexceptionhelper.convert(jdbcexceptionhelper.java:43)
- .......
- caused by: com.mysql.jdbc.exceptions.mysqlnontransientconnect
ionexception: no operations allowed after connection closed.connection was implicitly closed due to underlying exception/error: - ** begin nested exception **
- com.mysql.jdbc.communicationsexception
- message: communications link failure due to underlying exception:
- ** begin nested exception **
- java.net.socketexception
- message: broken pipe
- stacktrace:
- java.net.socketexception: broken pipe
- at java.net.socketoutputstream.socketwrite0(native method)
- ......
- ** 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:
- //set to 'select 1'
- validationquery = "select 1"
- //set to 'true'
- testwhileidle = "true"
- //some positive integer
- timebetweenevictionrunsmillis = 3600000
- //set to something smaller than 'wait_timeout'
- minevictableidletimemillis = 18000000
- //if you don't mind a hit for every getconnection(), set to "true"
- testonborrow = "true"
c3p0增加以下配置信息:
- //获取connnection时测试是否有效
- testconnectiononcheckin = true
- //自动测试的table名称
- automatictesttable=c3p0testtable
- //set to something much less than wait_timeout, prevents connections from going stale
- idleconnectiontestperiod = 18000
- //set to something slightly less than wait_timeout, preventing 'stale' connections from being handed out
- maxidletime = 25000
- //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:
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
jdbc.checkouttimeout=3000
