Mysqli module error «Too many connections»

Symptoms

The site is down or failing to connect to the database. The site log contains an error of the following format:

 PHP Warning:  mysqli_real_connect(): (HY000/1040): Too many connections in /var/www/www-root/data/www/exmaple.com/dbconnection.php on line 10

Causes

The maximum number of database connections is exceeded.

Solution

Go to Databases - Database Servers, select the desired DBMS, click Database server settings, change the max-connections parameter. The default value is 151.