Using --max-jobs

[Phil <phil@beadling.co.uk>]

Hi all,

A few questions about running multiple build jobs in parallel:

According to the manual the number of build users (eg guixbuilder01)
determines how many jobs can be run in parallel.

If we have 10 guix builder accounts and do not specify --max-jobs
explicitly, does this mean that 10 builds can be done in parallel - i.e
10 invocations of "guix build" will run in parallel, for example?

If I set the daemon to --max-jobs=4, will that restrict it to 4 builds
in parallel, even if more guix builder accounts exist?  If yes, then are
further builds queued until an available account becomes available, or do
they fail?

Are these conditions changed by the introduction of a machines.scm?  i.e. if we
have a build farm containing 4 machines, each with 10 guix builder
accounts, will parallel building still be restricted to the 10 guix
builder accounts on the parent machine (the machine with the machines.scm)?

I see that settting --max-jobs to 0 and having machines to offload to
results in no builds taking place on the parent.  I understand if no
machines are contactable the build will fail?  However, what happens if all
machines in the machines.scm are already busy (no slots available)?
Does any further build request fail, or is it queued?  If --max-jobs is
set to 0 on the parent, are builds still restricted by the number of
build users on the parent box?


Thanks!
Phil.