We rely on memcache pretty heavily at Tumblr, with over 10TB of cache memory available across the stack. One of the things we’ve historically had a challenging time with at Tumblr is finding hot keys. A hot key is a memcache key getting dramatically more activity than other keys….
I do love a good scaling story. Hardware these days is so cheap that solutions such as a 10TB memory cache is achievable without a relatively large cost. Cloud computing has opened up the possibilities for people to really push the limits of what is possible.