This query was performing badly. The solution seems to be to add a
redundant JOIN and WHERE to the subquery.
I renamed the table aliases in the subquery to avoid name collisions
elsewhere. I am afraid that makes the diff rather unhelpful. The
AND subq_qu.component = :qubacomponent2
line is new. The other lines have just had subq_ added.
The settings control the display options used when a user
first previews a question in the question bank. Once a
user has previewed some questions, these are stored as user
preferences.
It may not seem worth making this configurable, but acutally
it is important when training new users to get them started
off using the right opitions.
It is useful, and possible, to update the display options without
restarting the question. You now only have to restart if you are
changing the maximum mark or the behaviour.
This adds cron code which looks for question previews that have not been
touched for more than 24 hours, and deletes them.
We try to delete previews immediately. For example if the user clicks
start again, then we immediately delete their previous preview. However,
we can't do that if they just close the preview window. Hence we need
some cron code to clean up old preview that have got left lying around.
Normally, this code will not have much to do, so it will be very fast,
so we can afford to run it every cron.
This has been implemented in such a way that in future it will be easy
to add other cron code to the question bank.
Sadly, to make this work on MySQL, we require a horrible hack in the
already hacky delete_usage_records_for_mysql function.
1. We need this so that, for example, when previewing a question from
the quiz editing page, the preview uses the filter settings, theme and
language set for that quiz and course.
