Determinate Nix 3.5: introducing lazy trees

a year ago

Lazy trees have been introduced in Determinate Nix version 3.5.2, based on upstream Nix 2.28.3.
Lazy trees improve efficiency in large repositories, especially monorepos, by reducing evaluation time and disk usage.
Initial release is opt-in only for cautious adoption.
Lazy trees scope file copying to only what is needed, using a virtual filesystem to minimize unnecessary operations.
Performance improvements include up to 3x faster evaluation and 20x less disk usage in some cases.
Example provided shows a reduction from 304MB to 13MB in disk usage with lazy trees enabled.
CI comparisons demonstrate significant performance gains, with evaluation time dropping from 11 seconds to 3.5 seconds.
A new warning is introduced for inefficient source specifications in derivations, recommending better practices.
Instructions for upgrading or installing Determinate Nix are provided for macOS and Linux.
Future improvements planned include better evaluation caching, parallel evaluation, and multi-threaded unpacking of flakes.

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