Writing the cache takes a very long time on Windows

[Shnatsel]

The post-run phase of rust-cache takes a long time on our CI in https://github.com/rustsec/rustsec, but only on Windows.

Here's a sample log that shows MacOS cache completing in 38 seconds: https://github.com/rustsec/rustsec/actions/runs/6002426049/job/16278755180?pr=969

And here's the same job on Windows-MSVC, with the post-run phase taking over 5 minutes: https://github.com/rustsec/rustsec/actions/runs/6002426049/job/16278755358?pr=969

This is something that we have consistently observed, not a one-off.

The job definition can be found here: https://github.com/rustsec/rustsec/blob/b6def7c9fa30d7da2b2f569a9cded0f041d68068/.github/workflows/cargo-audit.yml#L36-L54

[Shnatsel]

After talking to a few people about it, it seems that Github Actions Windows runners simply have very slow networking, so this is not something that can be easily fixed in this action.

It might be possible to improve slightly by increasing the compression ratio on Windows, for example.

[jqnatividad]

Writing the cache on Windows is just painfully slow compared to macOS and Linux action runners.
You would think that since GH is owned by Microsoft that they'd optimize the Windows runners a bit more.
Just wanted to add that any improvement on its performance would be much appreciated!

In my workflows though, it takes a very long time to compress the cache with a Zstd compression level of 10, and the network copy time is negligible by comparison.

https://github.com/jqnatividad/qsv/actions/runs/8535984799/job/23383567613

Maybe the compression level is too high?

[bukowa]

It's not about network, but this command:

"C:\Program Files\Git\usr\bin\tar.exe" -xf D:/a/_temp/e75808bb-fd10-4be7-8c4e-562c289751df/cache.tzst -P -C D:/a/tauri-e2e/tauri-e2e --force-local --use-compress-program "zstd -d"

I remember reading about this tar from git being just slow.
Should probably try with other software to unpack archive - and then if its faster make a PR detecting windows and using that.

[bukowa]

microsoft/Windows-Dev-Performance#27

[Shnatsel]

That seems to be a different issue. That one is about extraction, but the step that seems to take a long time is compression at the end.

[bukowa]

I migrated to https://github.com/actions/cache/blob/main/examples.md#rust---cargo

And even there Windows is slower both on extraction and compression *(but much better than rust-cache)

[Enduriel]

This is also an issue for me on windows, I can't view the original workflow files posted with this issue but for me the workflow takes almost 3 minutes to restore the cache (see here). It seems to be the extraction step that is taking forever for me, not compression.