The Nix Hour

Currently Playing: The Nix Hour #38 [evaluation caching and performance in Nix]

Questions can only be asked by voice or chat in the meeting: https://meet.jit.si/nix-hour Vote for the new Nix Hour time here: https://discourse.nixos.org/t/poll-nix-hour-iteration-3-new-date-and-time/30968 The Nix Hour is an open beginner-oriented Q&A-style lecture on Nix, where you can bring your questions and we’ll answer them with more context, examples, alternatives, tradeoffs and related topics. Files from this session: https://github.com/tweag/nix-hour/tree/master/38 Matrix room for questions, feedback and notifications: https://matrix.to/#/%23nix-hour:matrix.org Issue tracker for asynchronous questions: https://github.com/tweag/nix-hour/issues Previous sessions playlist: https://www.youtube.com/playlist?list=PLyzwHTVJlRc8yjlx4VR4LU5A5O44og9in For more information and updates, check out https://discourse.nixos.org/t/the-nix-hour-a-weekly-nix-qa-lecture-by-tweag/22767 00:00 Intro, vote for new Nix Hour time 00:58 Q: What does 2023 Nix cache? 02:35 Thunk evaluation is cached in memory 10:56 File import in-memory cache 14:03 Leveraging evaluation cache with let-in 17:32 Leveraging file import cache 19:40 On-disk evaluation cache for flakes 28:46 Rules for recursing into attrsets in nixpkgs 32:44 How is pkgs.pkgs populated 36:52 Debugging evaluation performance with NIX_SHOW_STATS 44:51 NIX_COUNT_CALLS and trace-function-calls 50:12 How it works with nixpkgs 52:34 Using hyperfine for benchmarking 52:48 Manual benchmarking using sta for reports 54:41 ofborg evaluation performance report for PRs 59:31 Outro, don't forget to vote for new time