After about a year of my site being online (currently Moodle 3.9) I have tried to install a few plugins (blocks and course mod) and got stuck in installation process. The request just timeouts and if you try again you get the same result.
After looking into source code of installation script I have found that Moodle purges all caches prior to installing a new plugin. This purging takes a long time in my case. So I have tried to purge cache via a cli script and it took about 3.5 - 4 hours. After that I have successfully installed my plugin.
So my question is how can I determine Moodle cache size and can it grow to take up all available disk space? How often to purge caches in production environment (purge_caches.php --other and purge_caches.php --muc)?