Hi Derrick, > This is a second attempt at redesigning Git's repository maintenance > patterns. The first attempt [1] included a way to run jobs in the background > using a long-lived process; that idea was rejected and is not included in > this series. A future series will use the OS to handle scheduling tasks. > > [1] > https://lore.kernel.org/git/pull.597.git.1585946894.gitgitgadget@xxxxxxxxx/ > > As mentioned before, git gc already plays the role of maintaining Git > repositories. It has accumulated several smaller pieces in its long history, > including: > > 1. Repacking all reachable objects into one pack-file (and deleting > unreachable objects). > 2. Packing refs. > 3. Expiring reflogs. > 4. Clearing rerere logs. > 5. Updating the commit-graph file. It's worth mentioning 'git worktree prune' as well. > > While expiring reflogs, clearing rererelogs, and deleting unreachable > objects are suitable under the guise of "garbage collection", packing refs > and updating the commit-graph file are not as obviously fitting. Further, > these operations are "all or nothing" in that they rewrite almost all > repository data, which does not perform well at extremely large scales. > These operations can also be disruptive to foreground Git commands when git > gc --auto triggers during routine use. > > This series does not intend to change what git gc does, but instead create > new choices for automatic maintenance activities, of which git gc remains > the only one enabled by default. > > The new maintenance tasks are: > > * 'commit-graph' : write and verify a single layer of an incremental > commit-graph. > * 'loose-objects' : prune packed loose objects, then create a new pack from > a batch of loose objects. > * 'pack-files' : expire redundant packs from the multi-pack-index, then > repack using the multi-pack-index's incremental repack strategy. > * 'fetch' : fetch from each remote, storing the refs in 'refs/hidden//'. As some of the previous discussions [1] have raised, I think 'prefetch' would communicate the refs' purpose better than just 'hidden'. In-fact, I would suggest naming the task 'prefetch' instead, just to avoid potential communication issue between 'git fetch' and 'git maintenance fetch'. [1]: https://lore.kernel.org/git/xmqqeet1y8wy.fsf@xxxxxxxxxxxxxxxxxxxxxx/ > > These tasks are all disabled by default, but can be enabled with config > options or run explicitly using "git maintenance run --task=". There are > additional config options to allow customizing the conditions for which the > tasks run during the '--auto' option. ('fetch' will never run with the > '--auto' option.) > > Because 'gc' is implemented as a maintenance task, the most dramatic change > of this series is to convert the 'git gc --auto' calls into 'git maintenance > run --auto' calls at the end of some Git commands. By default, the only > change is that 'git gc --auto' will be run below an additional 'git > maintenance' process. > > The 'git maintenance' builtin has a 'run' subcommand so it can be extended > later with subcommands that manage background maintenance, such as 'start', > 'stop', 'pause', or 'schedule'. These are not the subject of this series, as > it is important to focus on the maintenance activities themselves. > > An expert user could set up scheduled background maintenance themselves with > the current series. I have the following crontab data set up to run > maintenance on an hourly basis: > > 0 * * * * git -C /<path-to-repo> maintenance run --no-quiet >>/<path-to-repo>/.git/maintenance.log Perhaps the logging should be included inside the maintenance command instead of relying on the append here? Given that we have 'gc.log', I would imagine 'maintenance.log' is not too far-fetched? > > My config includes all tasks except the 'gc' task. The hourly run is > over-aggressive, but is sufficient for testing. I'll replace it with daily > when I feel satisfied. > > Hopefully this direction is seen as a positive one. My goal was to add more > options for expert users, along with the flexibility to create background > maintenance via the OS in a later series. > > OUTLINE > ======= > > Patches 1-4 remove some references to the_repository in builtin/gc.c before > we start depending on code in that builtin. > > Patches 5-7 create the 'git maintenance run' builtin and subcommand as a > simple shim over 'git gc' and replaces calls to 'git gc --auto' from other > commands. > > Patches 8-15 create new maintenance tasks. These are the same tasks sent in > the previous RFC. > > Patches 16-21 create more customization through config and perform other > polish items. > > FUTURE WORK > =========== > > * Add 'start', 'stop', and 'schedule' subcommands to initialize the > commands run in the background. > > > * Split the 'gc' builtin into smaller maintenance tasks that are enabled by > default, but might have different '--auto' conditions and more config > options. > > > * Replace config like 'gc.writeCommitGraph' and 'fetch.writeCommitGraph' > with use of the 'commit-graph' task. > > > > Thanks, -Stolee Thanks, Son Luong.
