mysql> SHOW PROCESSLIST;
+----+------+-----------------+------+---------+------+-------+------------------+
| Id | User | Host            | db   | Command | Time | State | Info             |
+----+------+-----------------+------+---------+------+-------+------------------+
|  3 | root | localhost:50274 | test | Query   |    0 | NULL  | SHOW PROCESSLIST |
+----+------+-----------------+------+---------+------+-------+------------------+
1 row in set (0.00 sec)
mysql>

mysql> show status like 'Threads%';  

+-------------------+-------+  

| Variable_name     | Value |  

+-------------------+-------+  

| Threads_cached    | 58    |  

| Threads_connected | 57    |###这个数值指的是打开的连接数  

| Threads_created   | 3676  |  

| Threads_running   | 4     |###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  

这是是查询数据库当前设置的最大连接数  

mysql> show variables like '%max_connections%';  

+-----------------+-------+  

| Variable_name   | Value |  

+-----------------+-------+  

| max_connections | 100   |  

+-----------------+-------+  

设置最大连接数

法一：可以在/etc/my.cnf里面设置数据库的最大连接数  

max_connections = 1000

法二：mysql> set global max_connections=1000;