Re: [PATCH 00/15] [RFC] Maintenance jobs and job runner

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Junio,

On Wed, 27 May 2020, Junio C Hamano wrote:

> Josh Steadmon <steadmon@google.com> writes:
>
> > Regardless of what happens with the job-runner, I would like to see a
> > top-level command that performs a single iteration of all the
> > recommended maintenance steps, with zero configuration required, on a
> > single repo. This gives an entry point for users who want to manage
> > their own maintenance schedule without running a background process.
> > ...
> >> Unix users will be unhappy with us if we use our own scheduling system
> >> when cron is available.  They will expect us to reimplement those
> >> features and they will complain if we do not.  While I cannot name
> >> names, there are a nontrivial number of large, enterprise monorepos that
> >> run only on macOS and Linux.
> >
> > Speaking purely as a user, I agree with this point. This is why I want a
> > single-iteration top-level maintenance command.
>
> Yes, well said.
>
> It exactly is what "git gc" was meant to be.  To put it differently,
> if you asked any non-novice end-user if there is one single command
> that s/he would use to keep a repository healthy, it is very likely
> that the answer would be "git gc".

The biggest problem with bringing up `git gc` in this context (and it is
actually a quite big problem) is that "gc" stands for "garbage
collection", and these maintenance tasks are not even close to being about
collecting garbage.

So while `git gc` looks like a good candidate on its technical merits, the
usability/discoverability point of view paints a very different picture.

What Scalar does is conceptually a _very_ different thing from letting
`git gc --auto` (which I guess is what you _actually_ meant, as I have yet
to meet even a single Git user outside of this mailing list who knows `git
gc`, let alone who runs it manually) determine whether loose objects
should be cleaned up and packs should be consolidated.

Like, pre-fetching a daily pack in preparation for the user fetching
updates. You could argue that this is, in a way, _accumulating_ "garbage".

The entire idea of those maintenance tasks is that they are _not_
triggered by the user, not even as a side effect (`git gc --auto` is very
much a side effect, and on Windows, where it does not `daemonize()`
because that concept does not translate well into the Win32 API, having it
run in the foreground is very much felt by the users).

Those maintenance tasks should stay out of the users' way as much as
possible.

> And having such a single point of entry would be a good thing.

I guess I would argue for the introduction of a new command, like `git
maintenance`, which could potentially trigger a `git gc --auto`, but is
primarily intended to run _outside_ of the users' work hours.

Once we have that, we can always figure out whether there is a convenient
way to register this via `crontab` or Windows Task Scheduler, without
asking the users to do all of these tedious steps manually. I, for one,
have to spend the extra time looking up what those positional numbers in
the `crontab` thing _mean_, _every_ _single_ _time_ I touch the `crontab`.
_Every_ _single_ _time_.

Therefore, I would like very much to have a `git maintenance --schedule`
(or something like that), even if only on Windows, on the grounds alone
that it is even more tedious to work with the Windows Task Scheduler. But
I would prefer to have that also in my Linux setup. The convenience for
the users (myself included) is just too compelling.

Ciao,
Dscho