bug#30290: guix-daemon slows to a crawl when a substitute server is offline

[zimoun]

Hi Maxim,

On Mon, 29 Jan 2018 at 22:07, Maxim Cournoyer <maxim.cournoyer@gmail.com> wrote:
> When a substitute server used by guix-daemon is offline, the daemon will
> keep attempting to connect to it, even when it shouldn't need any data
> (ran 'sudo guix system reconfigure my-config.scm' multiple times in a
> row.
>
> With the disconnected server (bayfront in my case), that command would
> take close to 8 minutes, with many system calls like:
>
> connect(14, {sa_family=AF_INET, sin_port=htons(443), 
> sin_addr=inet_addr("141.255.128.56")}, 16) = -1 EINPROGRESS
>
> which wasted 5 seconds each time.
>
> After removing this server from my substitute servers list, the same
> operation (system reconfigure) is 8 times faster (1 minute).
>
> Suggestion: the daemon should stop trying to use the offline substitute
> server after trying for X times, and print a warning about it.

This looks like as a wishlist, right?  Do it make sense to include such
feature to the recent discussions about the revamp of offloading,
Cuirass, publish, etc.


All the best,
simon