yii2查询很慢 Opening DB connection耗时很久 是什么原因导致的呢？ [ 2.0 版本 ]

求解：打开一个页面，trace发现opening db connection耗时是最久的，会是什么原因导致的呢

Performance Profiling  
Total processing time: 1,148 ms; Peak memory: 4.8 MB.  

Total 4 items.  
#	Time	Duration	Category	Info  
 	 	 	 	 
**1	18:08:05.189	1047.1 ms	yii\db\Connection::open	Opening DB connection: mysql:host=localhost;dbname=cms**  
2	18:08:06.236	1.0 ms	yii\db\Command::query	SELECT * FROM `t_link` ORDER BY `no`  
3	18:08:06.238	5.0 ms	yii\db\Command::query	SHOW FULL COLUMNS FROM `t_link`  
4	18:08:06.245	1.0 ms	yii\db\Command::query	SHOW CREATE TABLE `t_link`