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From: Leo Famulari <leo@famulari.name>
Subject: Re: Parallel downloads
Date: Tue, 12 Nov 2019 12:44:42 -0500
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To: Ludovic =?iso-8859-1?Q?Court=E8s?= <ludo@gnu.org>
Cc: guix-devel@gnu.org

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 ci.guix.gnu.org, than to
> download them sequentially.

Parallel downloading is not faster in terms of overall transfer rate
from ci.guix.gnu.org.

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.

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.