mysql 的max_connections和max_user_connections 的区别

时间:2022-03-17 07:36:31
----查看max_user_connections 默认值

MySQL
> show variables like 'max_user_connections';
+----------------------+-------+
| Variable_name | Value |
+----------------------+-------+
| max_user_connections | 0 |
+----------------------+-------+

1 row in set (0.00 sec)

---设置 max_user_connections
mysql
> set @@global.max_user_connections=1;

Query OK,
0 rows affected (0.03 sec)
mysql
> select @@max_user_connections;
+------------------------+
| @@max_user_connections |
+------------------------+
| 1 |
+------------------------+
1 row in set (0.00 sec)
上面参数设置完后窗口,要重新登陆一下

root@dg
~]# mysql -uroot -pmysql
然后再开一个窗口登陆就会报如下错误:
root@dg
~]# mysql -uroot -pmysql
Warning: Using a password on the command line
interface can be insecure.

ERROR
1203 (42000): User root already has more than 'max_user_connections' active connections



另外在登陆一个用户u2,正常登陆,但是在登陆一个u2用户,就会报错:
root@dg mysql]# mysql
-uu2 -pu2
Warning: Using a password on the command line
interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id
is 147
Server version:
5.6.27-enterprise-commercial-advanced MySQL Enterprise Server - Advanced Edition (Commercial)
Copyright (c)
2000, 2015, Oracle and/or its affiliates. All rights reserved.
Oracle
is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type
'help;' or '\h' for help. Type '\c' to clear the current input statement.


max_user_connections 针对用户设计的




下面我们来看看max_connections 的作用
mysql
> select @@max_connections;
+-------------------+
| @@max_connections |
+-------------------+
| 151 |
+-------------------+
1 row in set (0.00 sec)
mysql
> set @@global.max_connections=2;
Query OK,
0 rows affected (0.00 sec)
mysql
> select @@max_connections;
+-------------------+
| @@max_connections |
+-------------------+
| 2 |
+-------------------+
1 row in set (0.00 sec)
上面参数设置完后窗口,要重新登陆一下
[root@dg mysql]# mysql
-uroot -pmysql
在开一个窗口session2正常登陆:
[root@dg mysql]# mysql
-uroot -pmysql
再开第三个窗口,session3 登陆的时候报错
[root@dg
~]# mysql -uroot -pmysql
Warning: Using a password on the command line
interface can be insecure.
ERROR
1040 (HY000): Too many connections
[root@dg
~]# mysql -uu2 -pu2
Warning: Using a password on the command line
interface can be insecure.
ERROR
1040 (HY000): Too many connections


实验完毕后,改回原来的参数
mysql
> set @@global.max_user_connections=0;
Query OK,
0 rows affected (0.00 sec)

mysql
> select @@max_user_connections;
+------------------------+
| @@max_user_connections |
+------------------------+
| 0 |
+------------------------+
1 row in set (0.00 sec)
mysql
> set @@global.max_connections=200;
Query OK,
0 rows affected (0.00 sec)
mysql
> select @@max_connections;
+-------------------+
| @@max_connections |
+-------------------+
| 200 |
+-------------------+
1 row in set (0.00 sec)


结论:

max_user_connections:限制每个用户的session连接个数,例如max_user_connections
=1 ,那么用户u1只能连接的session数为1,如果还有用户u2,还是可以连接,但是连接数仍然为1
max_connections :是对整个服务器的用户限制,整个服务器只能开这么多session,而不考虑用户!