Re: Building and caching old Guix derivations for a faster time machine

[Guillaume Le Vaillant <glv@posteo.net>]

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Maxim Cournoyer <maxim.cournoyer@gmail.com> skribis:

> Hi Simon,
>
> Simon Tournier <zimon.toutoune@gmail.com> writes:
>
>> Hi,
>>
>> On mer., 22 nov. 2023 at 19:27, Ludovic Courtès <ludo@gnu.org> wrote:
>>
>>> For long-term storage though, we could choose to keep lzip only (because
>>> it compresses better).  Not something we can really do with the current
>>> ‘guix publish’ setup though.
>>
>> It looks good to me.  For me, the priority list looks like:
>
> I'd like to have a single archive type as well in the future, but I'd
> settle on Zstd, not lzip, because it's faster to compress and
> decompress, and its compression ratio is not that different when using
> its highest level (19).

Last time I checked, zstd with max compression (zstd --ultra -22) was
a little slower and had a little lower compression ratio than lzip with
max compression (lzip -9).
Zstd is however much faster for decompression.

Another thing that could be useful to consider is that lzip was designed
for long term storage, so it has some redundancy allowing fixing/recovering
a corrupt archive (e.g. using lziprecover) if there has been some bit
rot in the hardware storing the file.
Whereas as far as I know zstd will just tell you "error: bad checksum"
and will have no way to fix the archive.

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