The max_connections in MySQL 5.7 - mysql

Question

I met a problem, the value of max_connction in MySQL is 214 after I set it 1000 via edit the my.cnf, just like below:
hadoop#node1:~$ mysql -V
mysql Ver 14.14 Distrib 5.7.15, for Linux (x86_64) using EditLine wrapper
MySQL version: 5.7
OS version : ubuntu 16.04LTS
mysql> show variables like 'max_connections';
+-----------------+-------+
| Variable_name | Value |
+-----------------+-------+
| max_connections | 151 |
+-----------------+-------+
1 row in set (0.00 sec)
As we can see, the variable value of max_connections is 151. Then , I edit the configuration file of MySQL.
yang2#node1:~$ sudo vi /etc/mysql/my.cnf
[mysqld]
character-set-server=utf8
collation-server=utf8_general_ci
max_connections=1000
Restart MySQL service after save the configraion.
yang2#node1:~$ service mysql restart
==== AUTHENTICATING FOR org.freedesktop.systemd1.manage-units ===
Authentication is required to restart 'mysql.service'.
Multiple identities can be used for authentication:
1. yangqiang,,, (yang2)
2. ,,, (hadoop)
Choose identity to authenticate as (1-2): 1
Password:
==== AUTHENTICATION COMPLETE ===
yang2#node1:~$
Now, we guess the max_connection is 1000, really?
mysql> show variables like 'max_connections';
+-----------------+-------+
| Variable_name | Value |
+-----------------+-------+
| max_connections | 214 |
+-----------------+-------+
1 row in set (0.00 sec)
It is 214. I do not really understand this result, who can help me? thx!

Answer 1

You may set the value manually, e.g.
set global max_connections=500;
however, after a restart of MySQL the value is reset to 214.
The solution depends on the (version of) OS and the MySQL version. With Ubuntu 16.04 and MySQL >= 5.7.7 following works:
systemctl edit mysql
Enter
[Service]
LimitNOFILE=8000
save, this will create a new file
/etc/systemd/system/mysql.service.d/override.conf
and restart the server:
systemctl daemon-reload
systemctl restart mysql
For other environments: Can not increase max_open_files for Mysql max-connections in Ubuntu 15

Answer 2

As MySQL documentation on max_connections setting says:
Increasing this value increases the number of file descriptors that
mysqld requires. If the required number of descriptors are not
available, the server reduces the value of max_connections.
This means that probably your MySQL server does not have enough resources to maintain the required number of descriptors.
MySQL documentation on How MySQL Opens and Closes Tables makes it clear that:
The table_open_cache and max_connections system variables affect the
maximum number of files the server keeps open. If you increase one or
both of these values, you may run up against a limit imposed by your
operating system on the per-process number of open file descriptors.
Many operating systems permit you to increase the open-files limit,
although the method varies widely from system to system. Consult your
operating system documentation to determine whether it is possible to
increase the limit and how to do so.

Answer 3

Follow the following steps:
cp /lib/systemd/system/mysql.service /etc/systemd/system/
echo -e "\r\nLimitNOFILE=infinity" >> /etc/systemd/system/mysql.service
echo "LimitMEMLOCK=infinity" >> /etc/systemd/system/mysql.service
sudo systemctl daemon-reload
sudo service mysql restart
And change or add he following line into file /etc/mysql/mysql.conf.d/mysqld.cnf :
[mysqld]
max_connections=110
Just this!
#Mahdi_Mohammadi

Answer 4

1.Edit mysql service file
#sudo cat /etc/systemd/system/multi-user.target.wants/mysql.service
# MySQL systemd service file
[Unit]
Description=MySQL Community Server
After=network.target
[Install]
WantedBy=multi-user.target
[Service]
Type=forking
User=mysql
Group=mysql
PIDFile=/run/mysqld/mysqld.pid
PermissionsStartOnly=true
ExecStartPre=/usr/share/mysql/mysql-systemd-start pre
ExecStart=/usr/sbin/mysqld --daemonize --pid-file=/run/mysqld/mysqld.pid
TimeoutSec=600
Restart=on-failure
RuntimeDirectory=mysqld
RuntimeDirectoryMode=755
##this bellow for tuneup
LimitNOFILE=infinity
LimitMEMLOCK=infinity
2.edit /etc/mysql/mysql.conf.d/mysqld.cnf
max_connections = 99999

Answer 5

Add session required pam_limits.so in /etc/pam.d/common-session (usually is not present by default).
The in /etc/security/limits.conf you can add some limits:
* hard nofile 8192
* soft nofile 4096
Also check using ulimit -a the open files limit.
This you can increase with ulimit -n 4096
Make sure you reboot at the end.