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1 git-maintenance(1)
2 ==================
3
4 NAME
5 ----
6 git-maintenance - Run tasks to optimize Git repository data
7
8
9 SYNOPSIS
10 --------
11 [verse]
12 'git maintenance' run [<options>]
13 'git maintenance' start [--scheduler=<scheduler>]
14 'git maintenance' (stop|register|unregister)
15
16
17 DESCRIPTION
18 -----------
19 Run tasks to optimize Git repository data, speeding up other Git commands
20 and reducing storage requirements for the repository.
21
22 Git commands that add repository data, such as `git add` or `git fetch`,
23 are optimized for a responsive user experience. These commands do not take
24 time to optimize the Git data, since such optimizations scale with the full
25 size of the repository while these user commands each perform a relatively
26 small action.
27
28 The `git maintenance` command provides flexibility for how to optimize the
29 Git repository.
30
31 SUBCOMMANDS
32 -----------
33
34 run::
35 Run one or more maintenance tasks. If one or more `--task` options
36 are specified, then those tasks are run in that order. Otherwise,
37 the tasks are determined by which `maintenance.<task>.enabled`
38 config options are true. By default, only `maintenance.gc.enabled`
39 is true.
40
41 start::
42 Start running maintenance on the current repository. This performs
43 the same config updates as the `register` subcommand, then updates
44 the background scheduler to run `git maintenance run --scheduled`
45 on an hourly basis.
46
47 stop::
48 Halt the background maintenance schedule. The current repository
49 is not removed from the list of maintained repositories, in case
50 the background maintenance is restarted later.
51
52 register::
53 Initialize Git config values so any scheduled maintenance will
54 start running on this repository. This adds the repository to the
55 `maintenance.repo` config variable in the current user's global
56 config and enables some recommended configuration values for
57 `maintenance.<task>.schedule`. The tasks that are enabled are safe
58 for running in the background without disrupting foreground
59 processes.
60 +
61 The `register` subcommand will also set the `maintenance.strategy` config
62 value to `incremental`, if this value is not previously set. The
63 `incremental` strategy uses the following schedule for each maintenance
64 task:
65 +
66 --
67 * `gc`: disabled.
68 * `commit-graph`: hourly.
69 * `prefetch`: hourly.
70 * `loose-objects`: daily.
71 * `incremental-repack`: daily.
72 --
73 +
74 `git maintenance register` will also disable foreground maintenance by
75 setting `maintenance.auto = false` in the current repository. This config
76 setting will remain after a `git maintenance unregister` command.
77
78 unregister::
79 Remove the current repository from background maintenance. This
80 only removes the repository from the configured list. It does not
81 stop the background maintenance processes from running.
82
83 TASKS
84 -----
85
86 commit-graph::
87 The `commit-graph` job updates the `commit-graph` files incrementally,
88 then verifies that the written data is correct. The incremental
89 write is safe to run alongside concurrent Git processes since it
90 will not expire `.graph` files that were in the previous
91 `commit-graph-chain` file. They will be deleted by a later run based
92 on the expiration delay.
93
94 prefetch::
95 The `prefetch` task updates the object directory with the latest
96 objects from all registered remotes. For each remote, a `git fetch`
97 command is run. The configured refspec is modified to place all
98 requested refs within `refs/prefetch/`. Also, tags are not updated.
99 +
100 This is done to avoid disrupting the remote-tracking branches. The end users
101 expect these refs to stay unmoved unless they initiate a fetch. With prefetch
102 task, however, the objects necessary to complete a later real fetch would
103 already be obtained, so the real fetch would go faster. In the ideal case,
104 it will just become an update to a bunch of remote-tracking branches without
105 any object transfer.
106
107 gc::
108 Clean up unnecessary files and optimize the local repository. "GC"
109 stands for "garbage collection," but this task performs many
110 smaller tasks. This task can be expensive for large repositories,
111 as it repacks all Git objects into a single pack-file. It can also
112 be disruptive in some situations, as it deletes stale data. See
113 linkgit:git-gc[1] for more details on garbage collection in Git.
114
115 loose-objects::
116 The `loose-objects` job cleans up loose objects and places them into
117 pack-files. In order to prevent race conditions with concurrent Git
118 commands, it follows a two-step process. First, it deletes any loose
119 objects that already exist in a pack-file; concurrent Git processes
120 will examine the pack-file for the object data instead of the loose
121 object. Second, it creates a new pack-file (starting with "loose-")
122 containing a batch of loose objects. The batch size is limited to 50
123 thousand objects to prevent the job from taking too long on a
124 repository with many loose objects. The `gc` task writes unreachable
125 objects as loose objects to be cleaned up by a later step only if
126 they are not re-added to a pack-file; for this reason it is not
127 advisable to enable both the `loose-objects` and `gc` tasks at the
128 same time.
129
130 incremental-repack::
131 The `incremental-repack` job repacks the object directory
132 using the `multi-pack-index` feature. In order to prevent race
133 conditions with concurrent Git commands, it follows a two-step
134 process. First, it calls `git multi-pack-index expire` to delete
135 pack-files unreferenced by the `multi-pack-index` file. Second, it
136 calls `git multi-pack-index repack` to select several small
137 pack-files and repack them into a bigger one, and then update the
138 `multi-pack-index` entries that refer to the small pack-files to
139 refer to the new pack-file. This prepares those small pack-files
140 for deletion upon the next run of `git multi-pack-index expire`.
141 The selection of the small pack-files is such that the expected
142 size of the big pack-file is at least the batch size; see the
143 `--batch-size` option for the `repack` subcommand in
144 linkgit:git-multi-pack-index[1]. The default batch-size is zero,
145 which is a special case that attempts to repack all pack-files
146 into a single pack-file.
147
148 pack-refs::
149 The `pack-refs` task collects the loose reference files and
150 collects them into a single file. This speeds up operations that
151 need to iterate across many references. See linkgit:git-pack-refs[1]
152 for more information.
153
154 OPTIONS
155 -------
156 --auto::
157 When combined with the `run` subcommand, run maintenance tasks
158 only if certain thresholds are met. For example, the `gc` task
159 runs when the number of loose objects exceeds the number stored
160 in the `gc.auto` config setting, or when the number of pack-files
161 exceeds the `gc.autoPackLimit` config setting. Not compatible with
162 the `--schedule` option.
163
164 --schedule::
165 When combined with the `run` subcommand, run maintenance tasks
166 only if certain time conditions are met, as specified by the
167 `maintenance.<task>.schedule` config value for each `<task>`.
168 This config value specifies a number of seconds since the last
169 time that task ran, according to the `maintenance.<task>.lastRun`
170 config value. The tasks that are tested are those provided by
171 the `--task=<task>` option(s) or those with
172 `maintenance.<task>.enabled` set to true.
173
174 --quiet::
175 Do not report progress or other information over `stderr`.
176
177 --task=<task>::
178 If this option is specified one or more times, then only run the
179 specified tasks in the specified order. If no `--task=<task>`
180 arguments are specified, then only the tasks with
181 `maintenance.<task>.enabled` configured as `true` are considered.
182 See the 'TASKS' section for the list of accepted `<task>` values.
183
184 --scheduler=auto|crontab|systemd-timer|launchctl|schtasks::
185 When combined with the `start` subcommand, specify the scheduler
186 for running the hourly, daily and weekly executions of
187 `git maintenance run`.
188 Possible values for `<scheduler>` are `auto`, `crontab`
189 (POSIX), `systemd-timer` (Linux), `launchctl` (macOS), and
190 `schtasks` (Windows). When `auto` is specified, the
191 appropriate platform-specific scheduler is used; on Linux,
192 `systemd-timer` is used if available, otherwise
193 `crontab`. Default is `auto`.
194
195
196 TROUBLESHOOTING
197 ---------------
198 The `git maintenance` command is designed to simplify the repository
199 maintenance patterns while minimizing user wait time during Git commands.
200 A variety of configuration options are available to allow customizing this
201 process. The default maintenance options focus on operations that complete
202 quickly, even on large repositories.
203
204 Users may find some cases where scheduled maintenance tasks do not run as
205 frequently as intended. Each `git maintenance run` command takes a lock on
206 the repository's object database, and this prevents other concurrent
207 `git maintenance run` commands from running on the same repository. Without
208 this safeguard, competing processes could leave the repository in an
209 unpredictable state.
210
211 The background maintenance schedule runs `git maintenance run` processes
212 on an hourly basis. Each run executes the "hourly" tasks. At midnight,
213 that process also executes the "daily" tasks. At midnight on the first day
214 of the week, that process also executes the "weekly" tasks. A single
215 process iterates over each registered repository, performing the scheduled
216 tasks for that frequency. Depending on the number of registered
217 repositories and their sizes, this process may take longer than an hour.
218 In this case, multiple `git maintenance run` commands may run on the same
219 repository at the same time, colliding on the object database lock. This
220 results in one of the two tasks not running.
221
222 If you find that some maintenance windows are taking longer than one hour
223 to complete, then consider reducing the complexity of your maintenance
224 tasks. For example, the `gc` task is much slower than the
225 `incremental-repack` task. However, this comes at a cost of a slightly
226 larger object database. Consider moving more expensive tasks to be run
227 less frequently.
228
229 Expert users may consider scheduling their own maintenance tasks using a
230 different schedule than is available through `git maintenance start` and
231 Git configuration options. These users should be aware of the object
232 database lock and how concurrent `git maintenance run` commands behave.
233 Further, the `git gc` command should not be combined with
234 `git maintenance run` commands. `git gc` modifies the object database
235 but does not take the lock in the same way as `git maintenance run`. If
236 possible, use `git maintenance run --task=gc` instead of `git gc`.
237
238 The following sections describe the mechanisms put in place to run
239 background maintenance by `git maintenance start` and how to customize
240 them.
241
242 BACKGROUND MAINTENANCE ON POSIX SYSTEMS
243 ---------------------------------------
244
245 The standard mechanism for scheduling background tasks on POSIX systems
246 is cron(8). This tool executes commands based on a given schedule. The
247 current list of user-scheduled tasks can be found by running `crontab -l`.
248 The schedule written by `git maintenance start` is similar to this:
249
250 -----------------------------------------------------------------------
251 # BEGIN GIT MAINTENANCE SCHEDULE
252 # The following schedule was created by Git
253 # Any edits made in this region might be
254 # replaced in the future by a Git command.
255
256 0 1-23 * * * "/<path>/git" --exec-path="/<path>" for-each-repo --config=maintenance.repo maintenance run --schedule=hourly
257 0 0 * * 1-6 "/<path>/git" --exec-path="/<path>" for-each-repo --config=maintenance.repo maintenance run --schedule=daily
258 0 0 * * 0 "/<path>/git" --exec-path="/<path>" for-each-repo --config=maintenance.repo maintenance run --schedule=weekly
259
260 # END GIT MAINTENANCE SCHEDULE
261 -----------------------------------------------------------------------
262
263 The comments are used as a region to mark the schedule as written by Git.
264 Any modifications within this region will be completely deleted by
265 `git maintenance stop` or overwritten by `git maintenance start`.
266
267 The `crontab` entry specifies the full path of the `git` executable to
268 ensure that the executed `git` command is the same one with which
269 `git maintenance start` was issued independent of `PATH`. If the same user
270 runs `git maintenance start` with multiple Git executables, then only the
271 latest executable is used.
272
273 These commands use `git for-each-repo --config=maintenance.repo` to run
274 `git maintenance run --schedule=<frequency>` on each repository listed in
275 the multi-valued `maintenance.repo` config option. These are typically
276 loaded from the user-specific global config. The `git maintenance` process
277 then determines which maintenance tasks are configured to run on each
278 repository with each `<frequency>` using the `maintenance.<task>.schedule`
279 config options. These values are loaded from the global or repository
280 config values.
281
282 If the config values are insufficient to achieve your desired background
283 maintenance schedule, then you can create your own schedule. If you run
284 `crontab -e`, then an editor will load with your user-specific `cron`
285 schedule. In that editor, you can add your own schedule lines. You could
286 start by adapting the default schedule listed earlier, or you could read
287 the crontab(5) documentation for advanced scheduling techniques. Please
288 do use the full path and `--exec-path` techniques from the default
289 schedule to ensure you are executing the correct binaries in your
290 schedule.
291
292
293 BACKGROUND MAINTENANCE ON LINUX SYSTEMD SYSTEMS
294 -----------------------------------------------
295
296 While Linux supports `cron`, depending on the distribution, `cron` may
297 be an optional package not necessarily installed. On modern Linux
298 distributions, systemd timers are superseding it.
299
300 If user systemd timers are available, they will be used as a replacement
301 of `cron`.
302
303 In this case, `git maintenance start` will create user systemd timer units
304 and start the timers. The current list of user-scheduled tasks can be found
305 by running `systemctl --user list-timers`. The timers written by `git
306 maintenance start` are similar to this:
307
308 -----------------------------------------------------------------------
309 $ systemctl --user list-timers
310 NEXT LEFT LAST PASSED UNIT ACTIVATES
311 Thu 2021-04-29 19:00:00 CEST 42min left Thu 2021-04-29 18:00:11 CEST 17min ago git-maintenance@hourly.timer git-maintenance@hourly.service
312 Fri 2021-04-30 00:00:00 CEST 5h 42min left Thu 2021-04-29 00:00:11 CEST 18h ago git-maintenance@daily.timer git-maintenance@daily.service
313 Mon 2021-05-03 00:00:00 CEST 3 days left Mon 2021-04-26 00:00:11 CEST 3 days ago git-maintenance@weekly.timer git-maintenance@weekly.service
314 -----------------------------------------------------------------------
315
316 One timer is registered for each `--schedule=<frequency>` option.
317
318 The definition of the systemd units can be inspected in the following files:
319
320 -----------------------------------------------------------------------
321 ~/.config/systemd/user/git-maintenance@.timer
322 ~/.config/systemd/user/git-maintenance@.service
323 ~/.config/systemd/user/timers.target.wants/git-maintenance@hourly.timer
324 ~/.config/systemd/user/timers.target.wants/git-maintenance@daily.timer
325 ~/.config/systemd/user/timers.target.wants/git-maintenance@weekly.timer
326 -----------------------------------------------------------------------
327
328 `git maintenance start` will overwrite these files and start the timer
329 again with `systemctl --user`, so any customization should be done by
330 creating a drop-in file, i.e. a `.conf` suffixed file in the
331 `~/.config/systemd/user/git-maintenance@.service.d` directory.
332
333 `git maintenance stop` will stop the user systemd timers and delete
334 the above mentioned files.
335
336 For more details, see `systemd.timer(5)`.
337
338
339 BACKGROUND MAINTENANCE ON MACOS SYSTEMS
340 ---------------------------------------
341
342 While macOS technically supports `cron`, using `crontab -e` requires
343 elevated privileges and the executed process does not have a full user
344 context. Without a full user context, Git and its credential helpers
345 cannot access stored credentials, so some maintenance tasks are not
346 functional.
347
348 Instead, `git maintenance start` interacts with the `launchctl` tool,
349 which is the recommended way to schedule timed jobs in macOS. Scheduling
350 maintenance through `git maintenance (start|stop)` requires some
351 `launchctl` features available only in macOS 10.11 or later.
352
353 Your user-specific scheduled tasks are stored as XML-formatted `.plist`
354 files in `~/Library/LaunchAgents/`. You can see the currently-registered
355 tasks using the following command:
356
357 -----------------------------------------------------------------------
358 $ ls ~/Library/LaunchAgents/org.git-scm.git*
359 org.git-scm.git.daily.plist
360 org.git-scm.git.hourly.plist
361 org.git-scm.git.weekly.plist
362 -----------------------------------------------------------------------
363
364 One task is registered for each `--schedule=<frequency>` option. To
365 inspect how the XML format describes each schedule, open one of these
366 `.plist` files in an editor and inspect the `<array>` element following
367 the `<key>StartCalendarInterval</key>` element.
368
369 `git maintenance start` will overwrite these files and register the
370 tasks again with `launchctl`, so any customizations should be done by
371 creating your own `.plist` files with distinct names. Similarly, the
372 `git maintenance stop` command will unregister the tasks with `launchctl`
373 and delete the `.plist` files.
374
375 To create more advanced customizations to your background tasks, see
376 launchctl.plist(5) for more information.
377
378
379 BACKGROUND MAINTENANCE ON WINDOWS SYSTEMS
380 -----------------------------------------
381
382 Windows does not support `cron` and instead has its own system for
383 scheduling background tasks. The `git maintenance start` command uses
384 the `schtasks` command to submit tasks to this system. You can inspect
385 all background tasks using the Task Scheduler application. The tasks
386 added by Git have names of the form `Git Maintenance (<frequency>)`.
387 The Task Scheduler GUI has ways to inspect these tasks, but you can also
388 export the tasks to XML files and view the details there.
389
390 Note that since Git is a console application, these background tasks
391 create a console window visible to the current user. This can be changed
392 manually by selecting the "Run whether user is logged in or not" option
393 in Task Scheduler. This change requires a password input, which is why
394 `git maintenance start` does not select it by default.
395
396 If you want to customize the background tasks, please rename the tasks
397 so future calls to `git maintenance (start|stop)` do not overwrite your
398 custom tasks.
399
400 CONFIGURATION
401 -------------
402
403 include::includes/cmd-config-section-all.txt[]
404
405 include::config/maintenance.txt[]
406
407
408 GIT
409 ---
410 Part of the linkgit:git[1] suite