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Knowledge Base

A website is not responding when a database backup/copy operation is running in Plesk: Error establishing a database connection

 
apachebackupbackup restore migrationcentosdatabase

Symptoms

  • When backing up or copying a large MySQL database in Plesk, the website that uses this database stops responding. CLOSE_WAIT connections can be observed on the server:

    # netstat -tanp | grep apache | awk '{print $6}' | sort | uniq -c | sort -n
    2 LISTEN
    24 ESTABLISHED
    62 CLOSE_WAIT

  • During a server-wide Plesk backup, all websites are not accessible with one of the following errors:

    Error establishing a database connection


    504 gateway timeout

  • When connecting to the database of an affected website directly via MySQL, the operation fails with the following error message:

    ERROR 1203 (42000): User database_admin_user already has more than 'max_user_connections' active connections

    or the following error when connecting via phpMyAdmin at Domains > example.com > Databases > database_name:

    mysqli::real_connect(): (HY000/1203): User database_admin_user already has more than 'max_user_connections' active connections

Cause

By default, mysqldumputility locks all tables and after that performs a data backup which leads to an increase in the number of connections waiting in the queue.

Resolution

Enable single-transaction option and disable lock-tables in MySQL configuration:

  1. Connect to the Plesk server via SSH.

  2. Open MySQL configuration file my.cnf 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

  3. Add these options at the end of the file:

    [mysqldump]
    skip-lock-tables
    single-transaction

  4. Save the changes and close the file.

Note: According to official MariaDB documentation, this configuration is a much better option for transactional tables such as InnoDB, because it does not need to lock the tables at all.

 

Currently, the option single-transaction can be enabled only globally via MySQL configuration file my.cnf.
If you wish to see more flexible options for database backup/copy operations in Plesk, vote for this feature request on Plesk UserVoice:

  • https://plesk.uservoice.com/forums/184549-feature-suggestions/suggestions/45790528
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