Database backup in Plesk fails because of missing MySQL/MariaDB user: The user specified as a definer does not exist

Symptoms

• A backup task finishes with the following warning message in Plesk:

  PLESK_ERROR: Warning: mysql "db_name"
  Not all the data was backed up into /var/lib/psa/dumps/domains/example.com/databases/db_name successfully. Total space: 18.00 GB; Available space: 11.00 GB; Mounted on: /. mysqldump: Got error: 1449: "The user specified as a definer ('db_user'@'%') does not exist" when using LOCK TABLES

• When exporting a MySQL / MariaDB database at Domains > example.com > Databases > db_name > Export Dump, the operation fails with:

  PLESK_ERROR: Unable to export a dump of db_name:
  mysqldump: Got error: 1045: "Access denied for user 'db_user'@'%' (using password: YES)" when using LOCK TABLES

• When opening views in phpMyAdmin, the page fails to load with:

  CONFIG_TEXT: #1449 - The user specified as a definer ('db_user'@'localhost') does not exist

  ---

  CONFIG_TEXT: #1045 - Access denied for user 'db_user'@'%' (using password: YES)

• Migration of a subscription fails in Plesk Migrator with the following error message:

  PLESK_ERROR: Failed to copy content of database 'dbname'
  Migration tools tried to perform operation in 3 attempts: Command execution failed on the source server 'source' (203.0.113.2) with non-zero exit code.
  ...
  exit code: 2
  stdout:
  stderr: mysqldump: Got error: 1449: The user specified as a definer ('old-dbuser'@'%') does not exist when using LOCK TABLES

Cause

The MySQL / MariaDB user set as a definer in the MySQL / MariaDB view is missing in the system or has different "Access control" setting.

Resolution