mysql>  show status like 'Threads%'
    -> ;
+-------------------+-------+
| Variable_name     | Value |
+-------------------+-------+
| Threads_cached    | 7     |
| Threads_connected | 16    | ##这个数值指的是打开的连接数  
| Threads_created   | 812   |
| Threads_running   | 2     | ##这个数值指的是激活的连接数
+-------------------+-------+
4 rows in set

mysql> show variables like '%max_connections%';
+------------------------+-------+
| Variable_name          | Value |
+------------------------+-------+
| max_connections        | 1000  |  这是当前设置的最大连接数 
| mysqlx_max_connections | 1000  |
+------------------------+-------+
2 rows in set

    可以在/etc/my.cnf里面设置数据库的最大连接数  
    max_connections = 1000