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

From: Derrick Stolee <stolee@gmail.com>
Date: Apr 4, 2020, 00:16 UTC
Message-ID: <cc9df614-2736-7cdd-006f-59878ee551c8@gmail.com>
In-Reply-To: <xmqqv9mgxn7u.fsf@gitster.c.googlers.com>

On 4/3/2020 5:40 PM, Junio C Hamano wrote:

Show 17 quoted lines

> "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.

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.

Sometimes it is hard to remember that people use Git because it is an important tool for getting their work done. Time waiting for Git to do a slow operation or being blocked on a triggered "git gc --auto" is time they would rather be doing what they want to do. Background maintenance is a way to reduce the time users spend blocked on Git and increase their productivity on the more important things.

Of course, I'm biased to using very large repositories where the existing maintenance process is insufficient. The design of these jobs is taken directly from what we designed and built for VFS for Git and Scalar over the winter of 2018-2019. These jobs were incredibly effective in cleaning up repositories that were accumulating cruft for over a year without any maintenance. Those repos have stayed clean and we haven't found more maintenance tasks to be necesary.

I still believe that there are plenty of repos of similar size to the Linux kernel that are in frequent use and could benefit from these operations.

Thanks, -Stolee