The blog post details a performance optimization for Nix's evaluation process. By pre-resolving store paths for built-in functions, specifically fetchers, Nix can avoid redundant computations during evaluation, leading to significant speed improvements. This is achieved by introducing a new builtins attribute in the Nix expression language containing pre-computed hashes for commonly used fetchers. This change eliminates the need to repeatedly calculate these hashes during each evaluation, resulting in faster build times, particularly noticeable in projects with many dependencies. The post demonstrates benchmark results showing a substantial reduction in evaluation time with this optimization, highlighting its potential to improve the overall Nix user experience.
This blog post details how to use Nix to manage persistent software installations on a Steam Deck, separate from the read-only SteamOS filesystem. The author leverages a separate ext4 partition formatted and mounted at /opt, where Nix stores its packages. This setup allows users to install and manage software without affecting the integrity of the core system, offering a robust and reproducible environment. The guide covers partitioning, mounting, installing Nix, configuring the system to recognize the Nix store, and provides practical examples for installing and running applications like Discord and installing desktop environments like KDE Plasma. This approach offers a significant advantage for users seeking a more flexible and powerful software management solution on their Steam Deck.
Several commenters on Hacker News expressed skepticism about the practicality of using Nix on the Steam Deck, citing complexity, limited storage space, and potential performance impacts. Some suggested alternative solutions like using Flatpak or simply managing game installations through Steam directly. Others questioned the need for persistent packages at all for gaming. However, a few commenters found the approach interesting and appreciated the author's exploration of Nix on a non-traditional platform, showcasing its flexibility. Some acknowledged the potential benefits of reproducible environments, especially for development or modding. The discussion also touched on the steep learning curve of Nix and the need for better documentation and tooling to make it more accessible.
NixOS aims for reproducibility, but subtle discrepancies can arise. While package builds are generally deterministic thanks to Nix's controlled environment, issues like differing system times during builds, non-deterministic build processes within packages themselves, and reliance on external resources like network-fetched timestamps or random numbers can introduce variability. The author highlights these challenges and explores how they impact reproducibility in practice, demonstrating that while NixOS significantly improves build consistency, achieving perfect reproducibility requires careful attention and sometimes impractical restrictions. Flaky tests and varying build outputs are presented as evidence of these limitations, showcasing scenarios where identical Nix expressions produce different results.
Hacker News users discuss reproducibility issues encountered with NixOS, despite its declarative nature. Several commenters point out that while Nix excels at package reproducibility, issues arise from external factors like hardware differences (particularly GPUs and networking) and reliance on non-reproducible external resources like timestamps and random number generation. One compelling comment highlights the distinction between "build reproducibility" and "runtime reproducibility," arguing NixOS effectively achieves the former but struggles with the latter. Others suggest that focusing solely on bit-for-bit reproducibility is misplaced, and that NixOS's value lies in its robust declarative configuration and ease of rollback, even if perfect reproducibility remains a challenge. The importance of properly caching build dependencies for true reproducibility is also emphasized. Several users share anecdotal experiences with inconsistencies and difficulties reproducing specific configurations, especially when dealing with complex setups or proprietary drivers.
Summary of Comments ( 30 )
https://news.ycombinator.com/item?id=43026071
Hacker News users generally praised the technique described in the article for improving Nix evaluation performance. Several commenters highlighted the cleverness of pre-computing store paths, noting that it bypasses a significant bottleneck in Nix's evaluation process. Some expressed surprise that this optimization wasn't already implemented, while others discussed potential downsides, like the added complexity to the tooling and the risk of invalidating the cache if the store path changes. A few users also shared their own experiences with Nix performance issues and suggested alternative optimization strategies. One commenter questioned the significance of the improvement in practical scenarios, arguing that derivation evaluation is often not the dominant factor in overall build time.
The Hacker News post "Improved evaluation times with pre-resolved Nix store paths" discussing the linked blog post about optimizing Nix evaluation times has generated a moderate number of comments, mostly focusing on the technical aspects and implications of the proposed optimization.
Several commenters express interest and appreciation for the performance improvements achieved by pre-resolving Nix store paths. One commenter specifically mentions how significant the improvements are, particularly for larger projects where evaluation time can be a bottleneck. Another highlights the potential benefits this optimization could bring to projects using Nix flakes, which often involve numerous dependencies and complex evaluation graphs.
A significant portion of the discussion revolves around the intricacies of Nix's evaluation model and how this optimization interacts with it. One commenter delves into the technical details of how Nix resolves paths and how pre-resolution can avoid redundant work, leading to faster evaluation times. Another discusses the trade-offs involved in pre-computing these paths, noting that while it improves evaluation speed, it might introduce complexity in other areas. There's also a comment exploring the potential implications of this change for Nix's caching mechanisms.
Some commenters also raise questions about the implementation and practical applications of this optimization. One inquires about the feasibility of integrating this technique into Nix itself, while another asks about potential compatibility issues with existing Nix projects. A user questions the overall impact on real-world usage, wondering if the improvement is noticeable in typical development workflows. There is further discussion around specific aspects of the implementation, including the use of SHA256 hashes and the handling of dynamic dependencies.
Finally, there are a few comments that offer alternative perspectives or suggestions. One commenter proposes a different approach to optimizing Nix evaluation, suggesting that focusing on reducing the number of dependencies might be more effective. Another mentions related work in other build systems, drawing parallels and highlighting potential areas for cross-pollination.