A CXL progress The elephant is learning to dance

I bought some Intel Optane persistent memory modules some years back to run some tests on them and maybe even build a PMEM-based KV store. I even wrote some articles about Oracle database's usage of PMEM for low-latency (local) commits [1]. But soon after I bought the memory, Intel discontinued the entire product line. I'm guessing that there just wasn't enough interest in practice as there were plenty of other (software-based) alternatives and NVMe SSDs got really fast too.

I've seen grand announcements, partnerships & alliances and unveilings of exciting CXL products that you can not order for the last 6 years by now. Or some CXL modules that add only 64 GB of CXL DRAM while taking 8x PCIe5 lanes. Perhaps there's lots of testing action going on with with select hyperscalers, but it's slightly worrying that after 6 years of announcements by major vendors (Samsung, SK Hynix, etc), you still can't just order a couple of these devices for your own testing.

I think shared, external CXL memory arrays that are connected to multiple servers (like SAN storage, but for cache-coherent, directly CPU-connected memory) would enable a few very interesting use cases for database engines:

1) Shared, cache-coherent global buffer caches for small-to-medium sized DB clusters

2) Shared build-side of giant hash joins for SQL (so you don't need to shuffle, repartition or broadcast data for your large joins)

Let's hope that this technology is real enough to become mainstream and actually available to users.

[1]: https://tanelpoder.com/posts/testing-oracles-use-of-optane-p...