Intel-Linux-Processor-Microcode-Dat VS dysnomia

They have been sort of cracked, but it doesn't matter. The web or chain of trust of those updates from the vendor to the processor is what matters. They're at least CRC checked to prevent loading corrupt files.

https://ieeeaccess.ieee.org/featured-articles/reverseenginee...

https://github.com/intel/Intel-Linux-Processor-Microcode-Dat...

https://github.com/platomav/CPUMicrocodes

Is it anymore of a "magic incantation" than the linux-image-XYZ package which controls which OS kernel is installed?

If you want to see when Intel issues new microcode updates, it is all available on their GitHub: https://github.com/intel/Intel-Linux-Processor-Microcode-Dat...

It isn't clear if Haswell has this optimization. As an easy test you could run the zero-fill-bench linked in the post and check the fill0 vs fill1 numbers. If they are the same, Haswell probably never had this optimization in the first place.

Based on the Intel microcode release note [1] it doesn't seem like client HSW got any update this time, only HSX (Haswell Xeon).

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[1] https://github.com/intel/Intel-Linux-Processor-Microcode-Dat...

NixOS doesn't have much, if anything, in the way of state management for services like databases. The Nix-iest way I know of managing those things is to write Dysnomia plugins for those things. But you'll have to figure out managing their internal state yourself to do that, e.g., with something like Liquibase or Flyway or something like that.

Depends on how the state is stored. If it's in configuration, Nix generated it and it lives immutable in the Nix store, so Nix will just point out it to the old version on rollback.

If it's something like the content of a SQL database, which lives outside the Nix store and which Nix did not generate, you need some other tool (like a filesystem snapshot, maybe) to perform the rollback. I think CoW filesystems sometimes have performance issues with DBs, though, so I'm not sure that's always the approach you'd take.

The Nix ecosystem does have a fairly mature tool for managing stateful components that live outside the Nix store, though: https://github.com/svanderburg/dysnomia

It's been around for a long time. Idk who all is using it