what may be causing this error?

Question

[Tue Mar 29 07:28:39 2016] [error]  PHP Warning:  mysqli::mysqli(): (HY000/1040): Too many connections in /var/www/vhosts/spaceamigos.com/httpdocs/qa-include/qa-db.php on line 66

Comments

This error occurs with me also

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Have you tried searching Google? There are many results for this, e.g. http://stackoverflow.com/questions/5040048/php-mysql-too-many-connections-to-database-error

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Yes, I googled. But I did not find solution to the problem.
Q2A does not cause so many queries to the database normally.
On some days the site works normally and there are only one or two concurrent queries.