Re: When substitute download + decompression is CPU-bound

["Ludovic Courtès" <ludo@gnu.org>]

Hi Guillaume,

Guillaume Le Vaillant <glv@posteo.net> skribis:

> I compared gzip, lzip and zstd when compressing a 580 MB pack (therefore
> containing "subsitutes" for several packages) with different compression
> levels. Maybe the results can be of some use to someone.

It’s insightful, thanks a lot!

One takeaway for me is that zstd decompression remains an order of
magnitude faster than the others, regardless of the compression level.

Another one is that at level 10 and higher zstd achieves compression
ratios that are more in the ballpark of lzip.

If we are to change the compression methods used at ci.guix.gnu.org, we
could use zstd >= 10.

We could also drop gzip, but there are probably pre-1.1 daemons out
there that understand nothing but gzip¹, so perhaps that’ll have to
wait.  Now, compressing substitutes three times may be somewhat
unreasonable.

Thoughts?

Ludo’.

¹ https://guix.gnu.org/en/blog/2020/gnu-guix-1.1.0-released/