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Re: Parallel downloads

From: Ludovic Courtès
Subject: Re: Parallel downloads
Date: Sun, 17 Nov 2019 18:52:13 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux)

Hi Mark,

Mark H Weaver <address@hidden> skribis:

> For these reasons, I'm inclined to think that parallel downloads is the
> wrong approach.  If a single download process is not making efficient
> use of the available bandwidth, I'd be more inclined to look carefully
> at why it's failing to do so.  For example, I'm not sure if this is the
> case (and don't have time to look right now), but if the current code
> waits until a NAR has finished downloading before asking for the next
> one, that's an issue that could be fixed by use of HTTP pipelining,
> without multiplying the memory usage.

I agree.  There’s HTTP pipelining for narinfos but not for nars.  Worse,
before fetching a nar, we do a GET /nix-cache-info, and in fact we spawn
a new ‘guix substitute’ process for each download (for “historical

So there’s room for optimization there!


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