Ensure your test site has "Performance Info" enabled in Site Administration > Developer > Debugging settings Ensure your test site has the coursecattree cache set to use the default application file cache in Site Administration > Plugins > Caches > Configuration Go to Site Administration > Courses > Manage courses and categories Ensure you have several course categories Change the order of a course category by pressing the up or down arrow next to its entry in the list (this will invalidate the cache). Reload the page, and check the performance info for core/coursecattree in the footer. EXPECTED : The cachestore_file shows 0 hits, 3 misses and 2 sets (the whole tree is set in 1 key, and the last invalidation timestamp in a second. BEFORE FIX: The cachestore_file shows 0 hits, 3 misses and 2n + 4 sets where n is the number of categories. Reload the page again, and check the performance info for core/coursecattree in the footer. EXPECTED : The cachestore_file shows 2 hits, 0 misses and 0 sets. BEFORE FIX: The cachestore_file shows n + 1 hits, 0 misses and 0 sets where n is the number of categories, Purge all caches and reload the course and category management page again. In your file manager, look in $CFG->dataroot/cache/cachestore_file/default_application/core_coursecattree. EXPECTED : There should be 2 directories, each containing 1 file. BEFORE FIX: There should be 2n + 4 files across several directories.