If a course section description contains a Video.js player, a database connection will be kept open in a sleeping state to MySQL, for each user viewing the page, for 60-90 seconds at least.
- Add a media file (tested with mp4) to the description of a course section. Make sure to be using the VideoJS player.
- Use a MySQL tool like MySQL Workbench to view active connections to database
- In the browser, view the course containing the player
- Observe connections to MySQL
In addition to being able to see the issue directly in MySQL, the webserver log will also have a log entry for a request to the video file, of rougly the same duration as the MySQL connection.
I have been able to reproduce this on three different installations, one being a completely vanilla 3.3.
Changing to the HTML5 Video player is a workaround, as it does not exhibit the same behaviour.
This can be a severe issue if many students access a course containing a video simultaneously because the MySQL server can potentially run out of available connections, until some are released.