For a site with a lot of courses, and using groups extensively, the calendar event creation dialog can now be intolerably slow (up to 90s or more) to appear and to save.

Memory usage is also ludicrously high.

This is still a problem even with Ryan's calendar-performance-related patches all applied (MDL-60959, MDL-60960, MDL-60962, MDL-60963, MDL-60966, MDL-60958).

Profiling shows the problem to be calendar_get_all_allowed_types and its calling of groups_get_all_groups_for_courses.

When this is getting details for a large number of courses, which use a large number of groups, with a large number of members, this is far too expensive and completely unnecessary. All that is needed is the group id, course id, group name, and whether the user is a member of the group.

I have a fix that reduces the time required by an order of magnitude; it's not perfect, but demonstrates that significant improvement is possible in this area. Will attach it once I've tidied it up.