/nix-casync

A more efficient way to store and substitute Nix store paths

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nix-casync

A more efficient way to store and substitute Nix store paths.

Docs are a bit sparse right now, please refer to https://flokli.de/posts/2021-12-10-nix-casync-intro/ for a description on how this works.

Build

$ go build ./cmd/nix_casync/

Run

./nix_casync serve --cache-path=path/to/local

Uploading store paths

nix copy \
  --extra-experimental-features nix-command \
  --to "http://localhost:9000?compression=none" $storePath

Note on compression

While it's also possible to upload with narfile compression, this is only used to compress uploads into the binary cache.

nix-casync will decompress compressed narfile uploads on the fly, chunk the uncompressed payload, and serve those as /nar/$narhash.nar. It will also rewrite uploaded .narinfo files accordingly.

This will have some unintuitive implications - if you upload a to /nar/$filehash.nar.zst, the upload won't be available on that location (but at /nar/$narhash.nar).

This also means HTTP HEAD requests to "compressed locations" will 404, and as a result, Nix clients might end up uploading the same .nar files multiple times. 1

Generally, you only want to use compression if connectivity to the binary cache is bad, and if you do, use a fast compression algorithm, such as zstd.

Footnotes

  1. Nix won't upload the same store path multiple times, as it checks $outhash.narinfo for existence first - so this only applies to multiple .narinfo files referring to the same .nar file. ↩