Originally reported as part of MDLSITE-1028. When changing aggregation method on a forum on moodle.org you get a blank screen. This is due to the required regrading of students. The forum requests the rating code returns the grades for all users. See line 508 of /rating/lib.php for the specific query. the records that are returned are then passed around throughout the forum as it does further processing.

Due to the volume of users on moodle.org a maximum memory exception is occurring.