Grails连MySQL - 连接池超时问题

问题表象
上线后的Grails应用，第二天，第一次登陆总是提示密码错误，再登陆一下就能成功。

推测倒是很准确
肯定是Tomcat或MySQL的某处超时设置导致的

准确诊断
因为无法在开发环境下模拟问题，先想办法在服务器端记录日志
Grails集成了log4j，用起来超级简单，而且还支持“环境”选项。

log4j = {
    appenders {
        environments {
            production {
                file name: 'file', file: '/home/jcat/myoalog/myoa.log'
            }
            development {
                file name: 'file', file: 'c:\\myoa.log'
            }
        }
    }

    root {
        info 'stdout', 'file'
    }

    info 'grails.app', 'myoa.StaticFilter'
}

然后在日志中发现了问题（这个log并不是我设计的，而是Shiro框架源码里的，可见人家是专业的）
2013-05-20 16:12:45,582 [http-bio-8080-exec-40] ERROR util.JDBCExceptionReporter  - The last packet successfully received from the server was 282,966,727 milliseconds ago.  The last packet sent successfully to the server was 282,966,728 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.

2013-05-20 16:12:45,601 [http-bio-8080-exec-40] INFO  app.realm  - Unable to authenticate with myoa.DbRealm - could not execute query; nested exception is org.hibernate.exception.JDBCConnectionException: could not execute query

模拟错误
mysql> show global variables like 'wait_timeout';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| wait_timeout  | 28800 |
+---------------+-------+
1 row in set (0.00 sec)


--重启后失效
set global wait_timeout=60;  --60秒

--需要停机配置
cat /etc/my.cnf
[mysqld]
wait_timeout=60

有趣的是，连接池超时后，登录后的浏览器会话并不会超时，所以第一次刷新会报错，再刷新（并不需要登录）就正常工作了。

最终解决
有3个途径
1. 调大MySQL的timout时间，网上说，最大到21天左右
2. 修改Hibernate的连接池组件，采用更高级的c3p0  http://blog.csdn.net/nethibernate/article/details/6658855
3. 修改默认的DBCP连接池的配置
http://www.netingcn.com/dbcp-config.html
http://sacharya.com/grails-dbcp-stale-connections

【法1-推荐】

        dataSource {   
          //解决数据库连接池长期不用超时的问题
            properties {
                timeBetweenEvictionRunsMillis = 1000 * 60 * 60 * 3  //每3小时检查一次
                minEvictableIdleTimeMillis = 1000 * 60 * 60 * 3     //把超过3小时的空闲连接激活一次
                //这样最差的情况，一个连接最多空闲6小时，而MySQL配置的是8小时断开
            }
        }

【法2-这会导致从连接池拿连接之前都会执行一次select 1语句】

                testOnBorrow = true
                testWhileIdle = false
                testOnReturn = false
                validationQuery = "SELECT 1"