MySQL crashes periodically on Plesk: Out of memory

Symptoms

• Plesk and websites are down from time to time:

  PLESK_INFO: 503 Service Unavailable

  Or

  PLESK_INFO: Server Error
  500
  Zend_Db_Adapter_Exception
  SQLSTATE[HY000] [2002] Connection refused

  OR

  ERROR: PleskDBException: Unable to connect to database: mysql_connect(): Connection refused /var/lib/mysql/mysql.sock (Error code: 2002). Please check that database server is started and accessible. (Abstract.php:69)

• In the log file /var/log/mariadb/mariadb.log or /var/log/mysql/mysql.log, the following error messages are found:

  InnoDB: Fatal error: cannot allocate memory for the buffer pool
   [ERROR] Plugin 'InnoDB' init function returned error. 
   [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed. 
   [ERROR] mysqld: Out of memory (Needed 128917504 bytes) 
   [ERROR] mysqld: Out of memory (Needed 96681984 bytes)

• The following error messages can be found in the log file /var/log/messages:

  kernel: Free swap = 0kB kernel: Total swap = 2097148kB ...
   kernel: Out of memory: Kill process 21770 (mysqld) score 17 or sacrifice child 
   kernel: Killed process 21770 (mysqld) total-vm:2698392kB, anon-rss:24616kB, file-rss:0kB, shmem-rss:0kB

Cause

Insufficient amount of free RAM on the server.

Resolution

Contact the server administrator or provider to increase the amount of the server’s RAM and add swap if it is not enabled.

Additional Information

Plesk Release Notes: Hardware Requirements for Plesk Onyx

Plesk Release Notes: Hardware Requirements for Plesk Obsidian