"The area where we are having trouble right now is that purple section in the middle that says "memcaches". Specifically, we are having problems with memcachedb, which is where we store a bunch of precomputed listings, like all the listing pages, profile pages, inboxes; pretty much any list on reddit that is too expensive to calculate on the fly. A few years ago, we decided to md5 all of our cache keys. We did this because at the time memcached (which is what memcachedb is based on) could only take keys of a certain length. In fact, the version it is based on still has this limitation. MD5ing the keys was a good solution to this problem, so we thought." - Tracy