How to enable the MySQL/MariaDB slow query log and analyze it on a Plesk for Linux server

Kuzma Ivanov

Updated November 13, 2025 02:21

kb: how-to Plesk for Linux ABT: Group B

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How to enable the MySQL/MariaDB slow query log and analyze it?

Connect to your Plesk server via SSH.
Enable the MySQL/MariaDB slow query log in the MySQL/MariaDB configuration file my.cnf:

2.1. Open the my.cnf file in a text editor. In this example, we are using the vi editor:
- on CentOS/RHEL-based distributions
  
  # vi /etc/my.cnf
- on Debian/Ubuntu-based distributions
  
  # vi /etc/mysql/my.cnf
2.2. Add the records below under the [mysqld] section:

Note: For MySQL 5.6/MariaDB 5.5 and older versions, use log-slow-queries instead of slow_query_log_file.

CONFIG_TEXT: slow_query_log = 1
slow_query_log_file = /var/log/mysql-slow.log
long_query_time = 2
- where long_query_time - time taken by an SQL query to be executed in seconds. If a query takes longer than the value specified, this query will be recorded in the slow query log file.
2.3. Save the changes and close the file.
Create slow query log file /var/log/mysql-slow.log and adjust its ownership:

# touch /var/log/mysql-slow.log
# chown mysql:mysql /var/log/mysql-slow.log
Restart the MySQL/MariaDB service:

# service mysql restart && service mariadb restart
Start monitoring the slow query log file. Use the command mysqldumpslow to analyze it and print summary of the slow query log file.
For example, to print all slow queries that have already been recorded, run the command:

# mysqldumpslow -a /var/log/mysql-slow.log

The full list of mysqldumpslow options is available here.

To learn more about MySQL slow query log, see MySQL 5.7 Reference Manual: The Slow Query Log.