We have several course on OpenLearn with large number of students, e.g. http://www.open.edu/openlearn/science-maths-technology/succeed-maths-part-1/content-section-overview  has 19,102 student.

When you try to load the Single view report for such a course you get the error

Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 78 bytes) in .../lib/dml/pgsql_native_moodle_recordset.php on line 68

I assume this is to do with the drop-down listing all students on the course.