[bug#39734] [PATCH] scripts: Emit GC hint if free space is lower than absolute and relative threshold.

["Ludovic Courtès" <ludo@gnu.org>]

Hi!

Pierre Neidhardt <mail@ambrevar.xyz> skribis:

> See the original discussion:
>
> https://lists.gnu.org/archive/html/guix-devel/2020-02/msg00303.html

Oops, I’m lagging behind and had not seen it yet, sorry about that!

> Our users fall into 2 categories:
>
> - Those with a "small" store partition, say 25 GiB.
> - Those with a "big" store partition, say 1 TiB.
>
> If we use a relative threshold, users with a big partition will get
> a hint all the time.  This may mislead newcomers into thinking that they
> should run "guix gc" while they still have 50 GiB of free space.
>
> If we use an absolute threshold, users with a small partition will get a
> hint all the time.
>
> In both cases, the hints becomes irrelevant if it's triggered for the
> wrong reason.
>
> The fix is to use both thresholds and to check against the lowest one.
>
> Does that make more sense?

It does, yes.

So back to the original patch… I think we should use ‘size->number’ for
the absolute threshold.

I’m also still mildly reluctant to the addition of
‘GUIX_DISK_SPACE_WARNING_ABSOLUTE’ (one more variable and a weird
name—“absolute warning”?).  An option could be to allow
‘GUIX_DISK_SPACE_WARNING’ to optionally contain both thresholds.  These
would be valid values:

  1GiB;10%
  15            ;15% relative, and default absolute
  15%           ;same
  1G            ;1G absolute, and default relative

Thus ‘%disk-space-warning’ would hold a pair.

Does that make sense?

Apologies for the misunderstanding!

Ludo’.