SYNOPSIS
git maintenance run [<options>] git maintenance start [--scheduler=<scheduler>] git maintenance (stop|register|unregister) [<options>]
DESCRIPTION
Run tasks to optimize Git repository data, speeding up other Git commands and reducing storage requirements for the repository.
Git commands that add repository data, such as git add or git fetch,
are optimized for a responsive user experience. These commands do not take
time to optimize the Git data, since such optimizations scale with the full
size of the repository while these user commands each perform a relatively
small action.
The git maintenance command provides flexibility for how to optimize the
Git repository.
SUBCOMMANDS
- run
-
Run one or more maintenance tasks. If one or more
--taskoptions are specified, then those tasks are run in that order. Otherwise, the tasks are determined by whichmaintenance.<task>.enabledconfig options are true. By default, onlymaintenance.gc.enabledis true. - start
-
Start running maintenance on the current repository. This performs the same config updates as the
registersubcommand, then updates the background scheduler to rungit maintenance run --scheduledon an hourly basis. - stop
-
Halt the background maintenance schedule. The current repository is not removed from the list of maintained repositories, in case the background maintenance is restarted later.
- register
-
Initialize Git config values so any scheduled maintenance will start running on this repository. This adds the repository to the
maintenance.repoconfig variable in the current user’s global config, or the config specified by --config-file option, and enables some recommended configuration values formaintenance.<task>.schedule. The tasks that are enabled are safe for running in the background without disrupting foreground processes.The
registersubcommand will also set themaintenance.strategyconfig value toincremental, if this value is not previously set. Theincrementalstrategy uses the following schedule for each maintenance task:-
gc: disabled. -
commit-graph: hourly. -
prefetch: hourly. -
loose-objects: daily. -
incremental-repack: daily.
git maintenance registerwill also disable foreground maintenance by settingmaintenance.auto = falsein the current repository. This config setting will remain after agit maintenance unregistercommand. -
- unregister
-
Remove the current repository from background maintenance. This only removes the repository from the configured list. It does not stop the background maintenance processes from running.
The
unregistersubcommand will report an error if the current repository is not already registered. Use the--forceoption to return success even when the current repository is not registered.
TASKS
- commit-graph
-
The
commit-graphjob updates thecommit-graphfiles incrementally, then verifies that the written data is correct. The incremental write is safe to run alongside concurrent Git processes since it will not expire.graphfiles that were in the previouscommit-graph-chainfile. They will be deleted by a later run based on the expiration delay. - prefetch
-
The
prefetchtask updates the object directory with the latest objects from all registered remotes. For each remote, agit fetchcommand is run. The configured refspec is modified to place all requested refs withinrefs/prefetch/. Also, tags are not updated.This is done to avoid disrupting the remote-tracking branches. The end users expect these refs to stay unmoved unless they initiate a fetch. However, with the prefetch task, the objects necessary to complete a later real fetch would already be obtained, making the real fetch faster. In the ideal case, it will just become an update to a bunch of remote-tracking branches without any object transfer.
- gc
-
Clean up unnecessary files and optimize the local repository. "GC" stands for "garbage collection," but this task performs many smaller tasks. This task can be expensive for large repositories, as it repacks all Git objects into a single pack-file. It can also be disruptive in some situations, as it deletes stale data. See git-gc(1) for more details on garbage collection in Git.
- loose-objects
-
The
loose-objectsjob cleans up loose objects and places them into pack-files. In order to prevent race conditions with concurrent Git commands, it follows a two-step process. First, it deletes any loose objects that already exist in a pack-file; concurrent Git processes will examine the pack-file for the object data instead of the loose object. Second, it creates a new pack-file (starting with "loose-") containing a batch of loose objects. The batch size is limited to 50 thousand objects to prevent the job from taking too long on a repository with many loose objects. Thegctask writes unreachable objects as loose objects to be cleaned up by a later step only if they are not re-added to a pack-file; for this reason it is not advisable to enable both theloose-objectsandgctasks at the same time. - incremental-repack
-
The
incremental-repackjob repacks the object directory using themulti-pack-indexfeature. In order to prevent race conditions with concurrent Git commands, it follows a two-step process. First, it callsgit multi-pack-index expireto delete pack-files unreferenced by themulti-pack-indexfile. Second, it callsgit multi-pack-index repackto select several small pack-files and repack them into a bigger one, and then update themulti-pack-indexentries that refer to the small pack-files to refer to the new pack-file. This prepares those small pack-files for deletion upon the next run ofgit multi-pack-index expire. The selection of the small pack-files is such that the expected size of the big pack-file is at least the batch size; see the--batch-sizeoption for therepacksubcommand in git-multi-pack-index(1). The default batch-size is zero, which is a special case that attempts to repack all pack-files into a single pack-file. - pack-refs
-
The
pack-refstask collects the loose reference files and collects them into a single file. This speeds up operations that need to iterate across many references. See git-pack-refs(1) for more information.
OPTIONS
- --auto
-
When combined with the
runsubcommand, run maintenance tasks only if certain thresholds are met. For example, thegctask runs when the number of loose objects exceeds the number stored in thegc.autoconfig setting, or when the number of pack-files exceeds thegc.autoPackLimitconfig setting. Not compatible with the--scheduleoption. - --schedule
-
When combined with the
runsubcommand, run maintenance tasks only if certain time conditions are met, as specified by themaintenance.<task>.scheduleconfig value for each<task>. This config value specifies a number of seconds since the last time that task ran, according to themaintenance.<task>.lastRunconfig value. The tasks that are tested are those provided by the--task=<task>option(s) or those withmaintenance.<task>.enabledset to true. - --quiet
-
Do not report progress or other information over
stderr. - --task=<task>
-
If this option is specified one or more times, then only run the specified tasks in the specified order. If no
--task=<task>arguments are specified, then only the tasks withmaintenance.<task>.enabledconfigured astrueare considered. See the TASKS section for the list of accepted<task>values. - --scheduler=auto|crontab|systemd-timer|launchctl|schtasks
-
When combined with the
startsubcommand, specify the scheduler for running the hourly, daily and weekly executions ofgit maintenance run. Possible values for<scheduler>areauto,crontab(POSIX),systemd-timer(Linux),launchctl(macOS), andschtasks(Windows). Whenautois specified, the appropriate platform-specific scheduler is used; on Linux,systemd-timeris used if available, otherwisecrontab. Default isauto.
TROUBLESHOOTING
The git maintenance command is designed to simplify the repository
maintenance patterns while minimizing user wait time during Git commands.
A variety of configuration options are available to allow customizing this
process. The default maintenance options focus on operations that complete
quickly, even on large repositories.
Users may find some cases where scheduled maintenance tasks do not run as
frequently as intended. Each git maintenance run command takes a lock on
the repository’s object database, and this prevents other concurrent
git maintenance run commands from running on the same repository. Without
this safeguard, competing processes could leave the repository in an
unpredictable state.
The background maintenance schedule runs git maintenance run processes
on an hourly basis. Each run executes the "hourly" tasks. At midnight,
that process also executes the "daily" tasks. At midnight on the first day
of the week, that process also executes the "weekly" tasks. A single
process iterates over each registered repository, performing the scheduled
tasks for that frequency. Depending on the number of registered
repositories and their sizes, this process may take longer than an hour.
In this case, multiple git maintenance run commands may run on the same
repository at the same time, colliding on the object database lock. This
results in one of the two tasks not running.
If you find that some maintenance windows are taking longer than one hour
to complete, then consider reducing the complexity of your maintenance
tasks. For example, the gc task is much slower than the
incremental-repack task. However, this comes at a cost of a slightly
larger object database. Consider moving more expensive tasks to be run
less frequently.
Expert users may consider scheduling their own maintenance tasks using a
different schedule than is available through git maintenance start and
Git configuration options. These users should be aware of the object
database lock and how concurrent git maintenance run commands behave.
Further, the git gc command should not be combined with
git maintenance run commands. git gc modifies the object database
but does not take the lock in the same way as git maintenance run. If
possible, use git maintenance run --task=gc instead of git gc.
The following sections describe the mechanisms put in place to run
background maintenance by git maintenance start and how to customize
them.
BACKGROUND MAINTENANCE ON POSIX SYSTEMS
The standard mechanism for scheduling background tasks on POSIX systems
is cron(8). This tool executes commands based on a given schedule. The
current list of user-scheduled tasks can be found by running crontab -l.
The schedule written by git maintenance start is similar to this:
# BEGIN GIT MAINTENANCE SCHEDULE
# The following schedule was created by Git
# Any edits made in this region might be
# replaced in the future by a Git command.
0 1-23 * * * "/<path>/git" --exec-path="/<path>" for-each-repo --config=maintenance.repo maintenance run --schedule=hourly
0 0 * * 1-6 "/<path>/git" --exec-path="/<path>" for-each-repo --config=maintenance.repo maintenance run --schedule=daily
0 0 * * 0 "/<path>/git" --exec-path="/<path>" for-each-repo --config=maintenance.repo maintenance run --schedule=weekly
# END GIT MAINTENANCE SCHEDULEThe comments are used as a region to mark the schedule as written by Git.
Any modifications within this region will be completely deleted by
git maintenance stop or overwritten by git maintenance start.
The crontab entry specifies the full path of the git executable to
ensure that the executed git command is the same one with which
git maintenance start was issued independent of PATH. If the same user
runs git maintenance start with multiple Git executables, then only the
latest executable is used.
These commands use git for-each-repo --config=maintenance.repo to run
git maintenance run --schedule=<frequency> on each repository listed in
the multi-valued maintenance.repo config option. These are typically
loaded from the user-specific global config. The git maintenance process
then determines which maintenance tasks are configured to run on each
repository with each <frequency> using the maintenance.<task>.schedule
config options. These values are loaded from the global or repository
config values.
If the config values are insufficient to achieve your desired background
maintenance schedule, then you can create your own schedule. If you run
crontab -e, then an editor will load with your user-specific cron
schedule. In that editor, you can add your own schedule lines. You could
start by adapting the default schedule listed earlier, or you could read
the crontab(5) documentation for advanced scheduling techniques. Please
do use the full path and --exec-path techniques from the default
schedule to ensure you are executing the correct binaries in your
schedule.
BACKGROUND MAINTENANCE ON LINUX SYSTEMD SYSTEMS
While Linux supports cron, depending on the distribution, cron may
be an optional package not necessarily installed. On modern Linux
distributions, systemd timers are superseding it.
If user systemd timers are available, they will be used as a replacement
of cron.
In this case, git maintenance start will create user systemd timer units
and start the timers. The current list of user-scheduled tasks can be found
by running systemctl --user list-timers. The timers written by git
maintenance start are similar to this:
$ systemctl --user list-timers
NEXT LEFT LAST PASSED UNIT ACTIVATES
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
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
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.serviceOne timer is registered for each --schedule=<frequency> option.
The definition of the systemd units can be inspected in the following files:
~/.config/systemd/user/git-maintenance@.timer
~/.config/systemd/user/git-maintenance@.service
~/.config/systemd/user/timers.target.wants/git-maintenance@hourly.timer
~/.config/systemd/user/timers.target.wants/git-maintenance@daily.timer
~/.config/systemd/user/timers.target.wants/git-maintenance@weekly.timergit maintenance start will overwrite these files and start the timer
again with systemctl --user, so any customization should be done by
creating a drop-in file, i.e. a .conf suffixed file in the
~/.config/systemd/user/git-maintenance@.service.d directory.
git maintenance stop will stop the user systemd timers and delete
the above mentioned files.
For more details, see systemd.timer(5).
BACKGROUND MAINTENANCE ON MACOS SYSTEMS
While macOS technically supports cron, using crontab -e requires
elevated privileges and the executed process does not have a full user
context. Without a full user context, Git and its credential helpers
cannot access stored credentials, so some maintenance tasks are not
functional.
Instead, git maintenance start interacts with the launchctl tool,
which is the recommended way to schedule timed jobs in macOS. Scheduling
maintenance through git maintenance (start|stop) requires some
launchctl features available only in macOS 10.11 or later.
Your user-specific scheduled tasks are stored as XML-formatted .plist
files in ~/Library/LaunchAgents/. You can see the currently-registered
tasks using the following command:
$ ls ~/Library/LaunchAgents/org.git-scm.git*
org.git-scm.git.daily.plist
org.git-scm.git.hourly.plist
org.git-scm.git.weekly.plistOne task is registered for each --schedule=<frequency> option. To
inspect how the XML format describes each schedule, open one of these
.plist files in an editor and inspect the <array> element following
the <key>StartCalendarInterval</key> element.
git maintenance start will overwrite these files and register the
tasks again with launchctl, so any customizations should be done by
creating your own .plist files with distinct names. Similarly, the
git maintenance stop command will unregister the tasks with launchctl
and delete the .plist files.
To create more advanced customizations to your background tasks, see launchctl.plist(5) for more information.
BACKGROUND MAINTENANCE ON WINDOWS SYSTEMS
Windows does not support cron and instead has its own system for
scheduling background tasks. The git maintenance start command uses
the schtasks command to submit tasks to this system. You can inspect
all background tasks using the Task Scheduler application. The tasks
added by Git have names of the form Git Maintenance (<frequency>).
The Task Scheduler GUI has ways to inspect these tasks, but you can also
export the tasks to XML files and view the details there.
Note that since Git is a console application, these background tasks
create a console window visible to the current user. This can be changed
manually by selecting the "Run whether user is logged in or not" option
in Task Scheduler. This change requires a password input, which is why
git maintenance start does not select it by default.
If you want to customize the background tasks, please rename the tasks
so future calls to git maintenance (start|stop) do not overwrite your
custom tasks.
CONFIGURATION
Everything below this line in this section is selectively included from the git-config(1) documentation. The content is the same as what’s found there:
- maintenance.auto
-
This boolean config option controls whether some commands run
git maintenance run --autoafter doing their normal work. Defaults to true. - maintenance.strategy
-
This string config option provides a way to specify one of a few recommended schedules for background maintenance. This only affects which tasks are run during
git maintenance run --schedule=Xcommands, provided no--task=<task>arguments are provided. Further, if amaintenance.<task>.scheduleconfig value is set, then that value is used instead of the one provided bymaintenance.strategy. The possible strategy strings are:-
none: This default setting implies no tasks are run at any schedule. -
incremental: This setting optimizes for performing small maintenance activities that do not delete any data. This does not schedule thegctask, but runs theprefetchandcommit-graphtasks hourly, theloose-objectsandincremental-repacktasks daily, and thepack-refstask weekly.
-
- maintenance.<task>.enabled
-
This boolean config option controls whether the maintenance task with name
<task>is run when no--taskoption is specified togit maintenance run. These config values are ignored if a--taskoption exists. By default, onlymaintenance.gc.enabledis true. - maintenance.<task>.schedule
-
This config option controls whether or not the given
<task>runs during agit maintenance run --schedule=<frequency>command. The value must be one of "hourly", "daily", or "weekly". - maintenance.commit-graph.auto
-
This integer config option controls how often the
commit-graphtask should be run as part ofgit maintenance run --auto. If zero, then thecommit-graphtask will not run with the--autooption. A negative value will force the task to run every time. Otherwise, a positive value implies the command should run when the number of reachable commits that are not in the commit-graph file is at least the value ofmaintenance.commit-graph.auto. The default value is 100. - maintenance.loose-objects.auto
-
This integer config option controls how often the
loose-objectstask should be run as part ofgit maintenance run --auto. If zero, then theloose-objectstask will not run with the--autooption. A negative value will force the task to run every time. Otherwise, a positive value implies the command should run when the number of loose objects is at least the value ofmaintenance.loose-objects.auto. The default value is 100. - maintenance.incremental-repack.auto
-
This integer config option controls how often the
incremental-repacktask should be run as part ofgit maintenance run --auto. If zero, then theincremental-repacktask will not run with the--autooption. A negative value will force the task to run every time. Otherwise, a positive value implies the command should run when the number of pack-files not in the multi-pack-index is at least the value ofmaintenance.incremental-repack.auto. The default value is 10.
GIT
Part of the git(1) suite