show processlist
show variables like "max_connections";
set GLOBAL max_connections=1000;
mysql> show status like 'Threads%';
+-------------------+-------+
| Variable_name | Value |
+-------------------+-------+
| Threads_cached | 32 |
| Threads_connected | 10 |
| Threads_created | 50 |
| Threads_rejected | 0 |
| Threads_running | 1 |
+-------------------+-------+
5 rows in set (0.00 sec)
Threads_connected ：这个数值指的是打开的连接数.
Threads_running ：这个数值指的是激活的连接数，这个数值一般远低于connected数值.
Threads_connected 跟show processlist结果相同，表示当前连接数。准确的来说，Threads_running是代表当前并发数
查询数据库当前设置的最大连接数
