cqpweb is a web interface to corpora programmed in php and using a mysql database. We run it successfully (and for quite a time unchanged) on our server, but during the last week or so, some database queries started fail consistently.
We run ubuntu 14.04 LTS and do regular upgrades with
apt-get upgrade. Otherwise, we did not change the system configuration. I checked that disk space is not a problem.
Current versions of programs:
php --version PHP 5.5.9-1ubuntu4.24 (cli) (built: Mar 16 2018 12:41:43) Copyright (c) 1997-2014 The PHP Group Zend Engine v2.5.0, Copyright (c) 1998-2014 Zend Technologies with Zend OPcache v7.0.3, Copyright (c) 1999-2014, by Zend Technologies
mysql --version mysql Ver 14.14 Distrib 5.5.59, for debian-linux-gnu (x86_64) using readline 6.3
What can cause a database cache overload and how can I cure it? Rebboting the server does not help.