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ERROR 1040 (08004): Too many connections

For a long time, in the low version of MySQL, when the number of connections increases sharply and too many connections appear, it is often difficult. Today, I specially tested and recorded the operation in MySQL version 8.0.17. This feature has been available in previous versions of percona. There is no need to restart the service in the future

mysql> show variables like '%max_conn%';
+------------------------+---------+
| Variable_name          | Value   |
+------------------------+---------+
| max_connect_errors     | 1000000 |
| max_connections        | 1024    |
| mysqlx_max_connections | 100     |
+------------------------+---------+
3 rows in set (0.00 sec)

mysql> set global max_connections=2;
Query OK, 0 rows affected (0.00 sec)

#Management port

mysql> show variables like '%port%';
+--------------------------+-------+
| Variable_name            | Value |
+--------------------------+-------+
| admin_port               | 33062 |
| large_files_support      | ON    |
| mysqlx_port              | 33060 |
| mysqlx_port_open_timeout | 0     |
| port                     | 3306  |
| report_host              |       |
| report_password          |       |
| report_port              | 3306  |
| report_user              |       |
| require_secure_transport | OFF   |
+--------------------------+-------+
10 rows in set (0.02 sec)

Note: admin_ Port this parameter does not need to be specified explicitly. If your MySQL port is 3306, 33062 will be displayed here

#Open the first connection

[root@fudao_db_cluster_001 ~]#  mysql -utest_r -h 10.192.30.53 -p'f9p%VSfXxcY3kHLJmKIi'
mysql: [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 26
Server version: 8.0.17 MySQL Community Server - GPL

Copyright (c) 2000, 2019, 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>

#Open the second connection

[root@fudao_db_cluster_001 local]# mysql -utest_r -h 10.192.30.53 -p'f9p%VSfXxcY3kHLJmKIi'
mysql: [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 27
Server version: 8.0.17 MySQL Community Server - GPL

Copyright (c) 2000, 2019, 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>

#Open the third connection

[root@fudao_db_cluster_001 local]#  mysql -utest_r -h 10.192.30.53 -p'f9p%VSfXxcY3kHLJmKIi'
mysql: [Warning] Using a password on the command line interface can be insecure.
ERROR 1040 (08004): Too many connections
[root@fudao_db_cluster_001 local]#

#Log in locally with the management port

[root@fudao_db_cluster_001 local]# mysql -h 127.0.0.1 -uadmin_m -p'rA75MQy*R*y@KO4z%LZe' -P 33062
mysql: [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 29
Server version: 8.0.17 MySQL Community Server - GPL

Copyright (c) 2000, 2019, 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>

As can be seen from the above, when the number of ordinary users is full, they can only log in with the super user local 127.0.0.1 or localhost

[root@fudao_db_cluster_001 local]# mysql -h 10.192.30.53 -uadmin_m -p'rA75MQy*R*y@KO4z%LZe' -P 33062
mysql: [Warning] Using a password on the command line interface can be insecure.
ERROR 2003 (HY000): Can't connect to MySQL server on '10.192.30.53' (111)
[root@fudao_db_cluster_001 local]#