K/V stores have made incredible strides in recent years. And what's more the improvements don't seem to be slowing down. Every few months at least, a new paper comes out that shows some huge percentage increase in performance over prior state of the art.

A lot of this is due to the rollout of ultra-fast storage technology, in particular NVMe SSDs and Optane NVDIMMs. A whole lot of systems engineers are having their fundamental assumptions about software design thrown on the trash fire without even realising it. This industry transition is going to take many years to fully percolate into people's consciousness and into the software stacks we really use. They are just that fast.

Because they're so fast it also challenges the designs of existing data storage engines. Nicely RocksDB has become a standard platform for experimentation. Not every experimental KV store uses it (e.g. FASTER doesn't) but a lot do. RocksDB has a lot of useful features, so that's good. But to fully saturate this new hardware may well take totally new data structures. There are some great papers exploring this topic.

Saturating modern NVMe SSDs is difficult because they have very high degrees of internal parallelism. Even though latencies are very low, to get max performance you need to issue a lot of requests in parallel, so your whole software stack needs to be highly parallel at every level. For my entire life, CPUs and RAM have outpaced persistent storage to such a huge extent that the challenge was always to engineer around the limits of HDDs and so on. Modern SSD/Optane tech is so crazy that the challenge is now to engineer around the limits of CPUs, kernels, etc. That's going to take a lot of adjustment but is also one of the most incredibly exciting industry transitions I can think of.