mysql最大连接数试验

一、试验基础环境配置

1、查看当前数据库的最大连接数

mysql> show global variables like '%connect%';
+--------------------------+-----------------+
| Variable_name            | Value           |
+--------------------------+-----------------+
| character_set_connection | utf8            |
| collation_connection     | utf8_general_ci |
| connect_timeout          | 10              |
| init_connect             |                 |
| max_connect_errors       | 10              |
| max_connections          | 160             |
| max_user_connections     | 0               |
+--------------------------+-----------------+
7 rows in set (0.00 sec)

2、设置全局变量max_connections为3(基于试验目的，做测试)

mysql> set global max_connections=3;
Query OK, 0 rows affected (0.01 sec)

3、查看设置是否生效.max_connections已经设置为3.

mysql> show global variables like '%connect%';
+--------------------------+-----------------+
| Variable_name            | Value           |
+--------------------------+-----------------+
| character_set_connection | utf8            |
| collation_connection     | utf8_general_ci |
| connect_timeout          | 10              |
| init_connect             |                 |
| max_connect_errors       | 10              |
| max_connections          | 3               |
| max_user_connections     | 0               |
+--------------------------+-----------------+
7 rows in set (0.00 sec)

4、退出当前登陆，再次登陆查看是否生效.

mysql> exit
Bye

C:\Users\ArcerZhang>mysql -uroot -parcerzhang
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.5.28 MySQL Community Server (GPL)

Copyright (c) 2000, 2012, 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.

mysql> show global variables like '%connect%';
+--------------------------+-----------------+
| Variable_name            | Value           |
+--------------------------+-----------------+
| character_set_connection | utf8            |
| collation_connection     | utf8_general_ci |
| connect_timeout          | 10              |
| init_connect             |                 |
| max_connect_errors       | 10              |
| max_connections          | 3               |
| max_user_connections     | 0               |
+--------------------------+-----------------+
7 rows in set (0.00 sec)

二、查看当前数据库连接数

mysql> use arcerzhangdb;
Database changed
mysql> show processlist;
+----+------+-----------------+--------------+---------+------+-------+------------------+
| Id | User | Host            | db           | Command | Time | State | Info             |
+----+------+-----------------+--------------+---------+------+-------+------------------+
|  3 | root | localhost:53232 | arcerzhangdb | Query   |    0 | NULL  | show processlist |
+----+------+-----------------+--------------+---------+------+-------+------------------+
1 row in set (0.00 sec)

三、分别打开第二个、第三个、第四个、第五个CMD窗口登录数据库

Microsoft Windows [版本 10.0.10586]
(c) 2015 Microsoft Corporation。保留所有权利。

C:\Users\ArcerZhang>mysql -uroot -parcerzhang
ERROR 1040 (HY000): Too many connections

C:\Users\ArcerZhang>

打开第五个窗口

四、结论

第一个连接窗口为初始窗口，或者说叫做监控窗口.

第二个连接窗口应该算是我们设置max_connections=3后第一个真正意义上的连接用户.

第三个连接窗口应该算是我们设置max_connections=3后第二个真正意义上的连接用户.

第四个连接窗口应该算是我们设置max_connections=3后第三个真正意义上的连接用户.

所以当打开第五个窗口的时候，会报如下错误:

C:\Users\ArcerZhang>mysql -uroot -parcerzhang
ERROR 1040 (HY000): Too many connections