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Caching in effect. Below are sequential attempt attempts at accessing the default view of a forums heavy course course-v1:IDBx+IDB6x+2015_T2 where the comment count of the pinned posts are ~4000. Each of the 20 threads it is trying to load (limit=20), is taking too long for a query. After each refresh, more data gets cached and then the comment count for the next threads are fetched. After a few refreshes, this course will no longer show 500s and load.
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