超时机制

mysql连接的超时问题：Communications link failure

org.springframework.dao.RecoverableDataAccessException: 
### Error updating database.  Cause: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet successfully received from the server was 1,454,140 milliseconds ago.  The last packet sent successfully to the server was 1,454,141 milliseconds ago.
### The error may involve miCoupon.unfreeze-Inline
### The error occurred while setting parameters
### SQL: update mi_coupon set status = 1, consume_xiaomi_id = null, consume_order_id = null, lock_time = null where consume_order_id=? and status=2
### Cause: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet successfully received from the server was 1,454,140 milliseconds ago.  The last packet sent successfully to the server was 1,454,141 milliseconds ago.
; SQL []; Communications link failure

The last packet successfully received from the server was 1,454,140 milliseconds ago.  The last packet sent successfully to the server was 1,454,141 milliseconds ago.; nested exception is com.mysql.jdbc.e
xceptions.jdbc4.CommunicationsException: Communications link failure

The last packet successfully received from the server was 1,454,140 milliseconds ago.  The last packet sent successfully to the server was 1,454,141 milliseconds ago.
        at org.springframework.jdbc.support.SQLExceptionSubclassTranslator.doTranslate(SQLExceptionSubclassTranslator.java:98)
        at org.springframework.jdbc.support.AbstractFallbackSQLExceptionTranslator.translate(AbstractFallbackSQLExceptionTranslator.java:73)
        at org.springframework.jdbc.support.AbstractFallbackSQLExceptionTranslator.translate(AbstractFallbackSQLExceptionTranslator.java:82)
        at org.mybatis.spring.MyBatisExceptionTranslator.translateExceptionIfPossible(MyBatisExceptionTranslator.java:73)
        at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:446)
        at com.sun.proxy.$Proxy13.update(Unknown Source)
        at org.mybatis.spring.SqlSessionTemplate.update(SqlSessionTemplate.java:294)
        at com.xiaomi.bss2.dao.MiCouponDao.unfreeze(MiCouponDao.java:23)
        at com.xiaomi.bss2.service.MiCouponService.unfreeze(MiCouponService.java:27)
        at com.xiaomi.bss2.main.Bss2ServiceImpl.cancelOrder(Bss2ServiceImpl.java:63)
        at com.xiaomi.bss2.main.Bss2ServiceImpl$$FastClassBySpringCGLIB$$67f6d028.invoke(<generated>)
        at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
        at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:736)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
        at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:99)
        at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:282)
        at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
        at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:671)
        at com.xiaomi.bss2.main.Bss2ServiceImpl$$EnhancerBySpringCGLIB$$ea0735d6.cancelOrder(<generated>)
        at com.xiaomi.bss2.main.Bss2ServiceThriftImpl$1.handle(Bss2ServiceThriftImpl.java:35)
        at com.xiaomi.bss2.main.Bss2ServiceThriftImpl$1.handle(Bss2ServiceThriftImpl.java:32)
        at com.xiaomi.bss2.main.Bss2ServiceThriftImpl.handle(Bss2ServiceThriftImpl.java:87)
        at com.xiaomi.bss2.main.Bss2ServiceThriftImpl.cancelOrder(Bss2ServiceThriftImpl.java:32)
        at sun.reflect.GeneratedMethodAccessor233.invoke(Unknown Source)

原因分析：

MySQL连接时，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。connections如果空闲超过8小时，Mysql将其断开，
而DBCP连接池并不知道该connection已经失效，如果这时有Client请求connection，DBCP将该失效的Connection提供给Client，将会造成异常。
其中wait_timeout就是负责超时控制的变量，其时间为长度为28800s，就是8个小时，那么就是说MySQL的服务会在操作间隔8小时后断开，需要再次重连。