Using Redis as a LRU cache. Don't do it.

DISCLAIMER: This isn't a "bash redis" post. We use redis as a non-persistent key/value store here at Weebly and are happy with how it performs in that function. I'm thankful for all of the work Salvatore and the community have done into making redis a great key/value store. This post solely addresses using redis as a LRU cache replacement for memcached.

Ever since Danga Interactive's/LiveJournal's memcached burst on to the Internet scene, it has become the de facto general purpose caching application for people running larger scale Internet sites (or anyone just wanting to cache expensive operations). And why not? It's a pretty good program that's well written and has extensive library support. The major drawbacks to memcached are its slab allocator memory model and maximum object size at startup. Let's take a look at those.

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