Redis is nice but you take a huge speed hit depending on what you're doing, compared to using in-memory structures. Note that Redis can also persist to disk, either by forking or by writing an append-only op log that can be replayed for reloading or replication. Anyway, you have ignored the case where you want not only the data structures, but also the open network connections to persist across process restarts. That's what passing file descriptors through unix domain sockets lets you do.