静态查看:
``` sql
SHOW PROCESSLIST;
SHOW FULL PROCESSLIST;
SHOW VARIABLES LIKE '%max_connections%';
SHOW STATUS LIKE '%Connection%';
```
实时查看：
``` sql
mysql> show status like 'Threads%';
+-------------------+-------+
| Variable_name | Value |
+-------------------+-------+
| Threads_cached |
