MySqlDataReader reader = MySqlHelper.ExecuteReader
拿数据后并未执行reader.Close()
结果：
数据库连接池超限，后端跑一段时间后就会造成服务器崩掉
报错信息：
error connecting: Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool. This may have occurred because all pooled connections were in use and max pool size was reached.
查询各种之后得到结论： reader结果不关闭的话，当前数据库连接也不会关，由于前端在一直请求，就造成超过连接池的问题了
所以：如果用ExecuteReader，拿 到reader后的数据内容后一定要执行： reader.Close()