MySQL|too many connections怎么办？

一、设置参数

mysql> set global max_connections=1;Query OK, 0 rows affected (0.00 sec)

二、测试登录情况

--在root用户已经登录的情况下，普通用户无法继续登录

root@sky-a@/root # /mysql/mysql-8.0.22/bin/mysql -usky --socket=/mydata/test/test.sock -psky

mysql: [Warning] Using a password on the command line interface can be insecure.

ERROR 1040 (08004): Too many connections



--root可以再登录一次

root@sky-a@/root # 3306



mysql> show processlist;

+----+-----------------+-----------+------+---------+------+------------------------+------------------+

| Id | User            | Host      | db   | Command | Time | State                  | Info             |

+----+-----------------+-----------+------+---------+------+------------------------+------------------+

|  5 | event_scheduler | localhost | NULL | Daemon  |  331 | Waiting on empty queue | NULL             |

| 12 | root            | localhost | NULL | Sleep   |   22 |                        | NULL             |

| 15 | root            | localhost | NULL | Query   |    0 | init                   | show processlist |

+----+-----------------+-----------+------+---------+------+------------------------+------------------+

3 rows in set (0.00 sec)



--root再次登录报错

root@sky-a@/root # 3306

mysql: [Warning] Using a password on the command line interface can be insecure.

ERROR 1040 (HY000): Too many connections

结论就是超级用户可以额外登录一次，查看官网确认：

mysqld actually permits max_connections + 1 client connections. The extra connection is reserved for use by accounts that have the CONNECTION_ADMIN privilege (or the deprecated SUPER privilege)

三、其他方案

（1）使用gdb调整【生产尽量避免使用】

root@sky-a@/root # gdb -p 77472 -ex "set max_connections=5000" -batch--其中77472是指mysqld的进程id--查看确认已调整mysql> show variables like '%max_connections%';+------------------------+-------+| Variable_name          | Value |+------------------------+-------+| max_connections        | 5000  || mysqlx_max_connections | 100   |+------------------------+-------+2 rows in set (0.01 sec)

（2）使用admin_port连接

mysql> show variables like '%admin%';+---------------------------------+-----------------+| Variable_name                   | Value           |+---------------------------------+-----------------+| admin_address                   | 127.0.0.1       || admin_port                      | 33062           

--此时已经登录2个会话

mysql> show processlist;

+----+-----------------+-----------+------+---------+------+------------------------+------------------+

| Id | User            | Host      | db   | Command | Time | State                  | Info             |

+----+-----------------+-----------+------+---------+------+------------------------+------------------+

|  5 | event_scheduler | localhost | NULL | Daemon  |  331 | Waiting on empty queue | NULL             |

| 12 | root            | localhost | NULL | Sleep   |   22 |                        | NULL             |

| 15 | root            | localhost | NULL | Query   |    0 | init                   | show processlist |

+----+-----------------+-----------+------+---------+------+------------------------+------------------+

3 rows in set (0.00 sec)



--root再登录会报错

root@sky-a@/root # 3306

mysql: [Warning] Using a password on the command line interface can be insecure.

ERROR 1040 (HY000): Too many connections



--用root@'%'登录admin_port/admin_address，未赋权

root@sky-a@/root # /mysql/mysql-8.0.22/bin/mysql -uroot -P33062 -h127.0.0.1 -proot1234

mysql: [Warning] Using a password on the command line interface can be insecure.

ERROR 1227 (42000): Access denied; you need (at least one of) the SERVICE_CONNECTION_ADMIN privilege(s) for this operation



--赋权和localhost一样的权限，可以登录

root@sky-a@/root # /mysql/mysql-8.0.22/bin/mysql -uroot -P33062 -h127.0.0.1 -proot1234

mysql> show processlist;

+----+-----------------+-----------------+------+---------+------+------------------------+------------------+

| Id | User            | Host            | db   | Command | Time | State                  | Info             |

+----+-----------------+-----------------+------+---------+------+------------------------+------------------+

|  5 | event_scheduler | localhost       | NULL | Daemon  |  560 | Waiting on empty queue | NULL             |

| 12 | root            | localhost       | NULL | Sleep   |   11 |                        | NULL             |

| 15 | root            | localhost       | NULL | Sleep   |  229 |                        | NULL             |

| 17 | root            | 127.0.0.1:53594 | NULL | Query   |    0 | init                   | show processlist |

+----+-----------------+-----------------+------+---------+------+------------------------+------------------+

4 rows in set (0.00 sec)

即可通过具有SERVICE_CONNECTION_ADMIN权限的用户通过TCP/IP的方式连接至数据库。

PS：这两个参数都是静态参数，重启数据库才有效。

Setting admin_port has no effect if admin_address is not specified because in that case the server maintains no administrative network interface.