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Re: Parallel downloads

From: Ludovic Courtès
Subject: Re: Parallel downloads
Date: Sun, 17 Nov 2019 18:15:24 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux)


Leo Famulari <address@hidden> skribis:

> On Sat, Nov 09, 2019 at 06:40:56PM +0100, Ludovic Courtès wrote:
>> Like I wrote, it’s not that simple (we’d first need the daemon to
>> distinguish substitution jobs from other jobs, but note that there are
>> also “downloads” that are actually derivation builds), and it’s not
>> clear to me that it’s overall beneficial anyway: it’s not supposed to be
>> faster to download 10 things in parallel from, than to
>> download them sequentially.
> Parallel downloading is not faster in terms of overall transfer rate
> from
> However, installing things with Guix involves downloading a lot of very
> small files like derivations, and Guix spends a lot of time initiating
> these downloads.

Good point.

Note that .drv files are never downloaded, but nevertheless it’s true
that there are often small files like the “module-import-compiled”
things.  This happens when building a system, but not so much when
building a package, though.

> For example, I can download things at 100 megabits, but when Guix needs
> to sequentially download 50 10-kilobyte files, it may take an entire
> minute.
> So there is a huge speedup with parallel downloading.

One thing I’d like to get rid of is the initial HTTP GET for
/nix-cache-info which is completely useless now.  That could help a bit.


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