On 7/13/2020 2:18 AM, Son Luong Ngoc wrote: > 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. Good point. I'll also say "including, but not limited to:" >> 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/ Thanks for the reminder. I'll rename the task as you suggest. >> 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? I'll research gc.log and how that works. >> 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. Thank you! -Stolee
