We did benchmark local memcache, but accessing the strings over the network (even locally) was much much slower than sparkey. Redis would likely have been similar to memcache.

The savings came not just from avoiding redundant GC over the same 80MB, but also from not going through the churn involved with loading that data over the network on process startup.

We have a large codebase that's written against MRI, so it's non-trivial to just switch to something else.