Somehow plesk keeps querying the mysql database.

this is the query:

SELECT s.dom_id, s.sys_user_type, s.name, u.login, a.password, s.coldfusion,s.ssi, s.php, s.cgi, s.perl, s.python, s.asp, s.asp_dot_net FROM subdomains s, sys_users u LEFT OUTER JOIN accounts a ON a.id = u.account_id WHERE u.id = s.sys_user_id AND (s.dom_id = '[a_domain]')

And it never quits!

 

what is the page or utility generated the error message?

 

It is not really an error, but the process of checking the domains (or something like that) keeps running.