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

From: brian m. carlson <sandals@crustytoothpaste.net>
Date: Apr 7, 2020, 01:48 UTC
Message-ID: <20200407014829.GL6369@camp.crustytoothpaste.net>
In-Reply-To: <cc9df614-2736-7cdd-006f-59878ee551c8@gmail.com>

On 2020-04-04 at 00:16:21, Derrick Stolee wrote:

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> On 4/3/2020 5:40 PM, Junio C Hamano wrote:
> > "Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com> writes:
> > 
> >>  * git run-job <job-name>: This builtin will run a single instance of a
> >>    maintenance job.
> >> 
> >>  * git job-runner [--repo=<path>]: This builtin will run an infinite loop
> >>    that executes git run-job as a subcommand.
> > 
> > What does this have to do with "git", though?  IOW, why does this
> > have to be part of Git, so that those who would benefit from having
> > a mechanism that makes it easy to run regular maintenance tasks but
> > are not Git users (or those that want to do such maintenance tasks
> > that are not necessarily tied to "git") must use "git" to do so?
> > 
> > I'll find out later why it is so after reading thru 15 patches
> > myself, so no need to give a quick answer to the above; it was just
> > my knee-jerk reaction.
> 
> That's a reasonable reaction. The short version of my reasoning is that
> many many people _use_ Git but are not Git experts. While a Git expert
> could find the right set of commands to run and at what frequency to
> keep their repo clean, most users do not want to spend time learning
> these commands. It's also worth our time as contributors to select what
> a good set of non-intrusive maintenance tasks could be, and make them
> easily accessible to users.
> 
> This series gets us half of the way there: a user interested in doing
> background maintenance could figure out how to launch "git run-job" on
> a schedule for their platform, or to launch "git job-runner" at start-
> up. That's a lot simpler than learning how the commit-graph,
> multi-pack-index, prune-packed, pack-objects, and fetch builtins work
> with the complicated sets of arguments.

If there are periodic tasks that should be done, even if only on large repos, then let's have a git gc --periodic that does them. I'm not sure that fetch should be in that set, but nothing prevents users from doing "git fetch origin && git gc --periodic". Let's make it as simple and straightforward as possible.

As for handling multiple repositories, the tool to do that could be as simple as a shell script which reads from ~/.config/git/repo-maintenance (or whatever) and runs the same command on all of the repos it finds there, possibly with a subcommand to add and remove repos.

Show 7 quoted lines

> The second half would be to create a command such as
> 
> 	git please-run-maintenance-on-this-repo
> 
> that initializes the background jobs and enables them on the repo they
> are using. This allows the most casual of Git user to work efficiently
> on very large repositories.

I'm not opposed to seeing a tool that can schedule periodic maintenance jobs, perhaps in contrib, depending on whether other people think it should go. However, I think running periodic jobs is best handled on Unix with cron or anacron and not a custom tool or a command in Git.

I've dealt with systems that implemented periodic tasks without using the existing tools for doing that, and I've found that usually that's a mistake. Despite seeming straightforward, there are a lot of tricky edge cases to deal with and it's easy to get wrong.

We also don't have to reimplement all the features in the system scheduler and can let expert users use a different tool of their choice instead if cron (or the Windows equivalent) is not to their liking.

-- 
brian m. carlson: Houston, Texas, US
OpenPGP: https://keybase.io/bk2204