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
--task
options are specified, then those tasks are run in that order. Otherwise, the tasks are determined by whichmaintenance.
<task>.enabled
config options are true. By default, onlymaintenance.gc.enabled
is true. - start
-
Start running maintenance on the current repository. This performs the same config updates as the
register
subcommand, then updates the background scheduler to rungit
maintenance
run
--scheduled
on 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.repo
config 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
register
subcommand will also set themaintenance.strategy
config value toincremental
, if this value is not previously set. Theincremental
strategy uses the following schedule for each maintenance task:-
gc
: disabled. -
commit-graph
: hourly. -
prefetch
: hourly. -
loose-objects
: daily. -
incremental-repack
: daily.
git
maintenance
register
will also disable foreground maintenance by settingmaintenance.auto
=
false
in the current repository. This config setting will remain after agit
maintenance
unregister
command. -
- 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
unregister
subcommand will report an error if the current repository is not already registered. Use the--force
option to return success even when the current repository is not registered.
TASKS
- commit-graph
-
The
commit-graph
job updates thecommit-graph
files 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 .graph
files that were in the previouscommit-graph-chain
file. They will be deleted by a later run based on the expiration delay. - prefetch
-
The
prefetch
task updates the object directory with the latest objects from all registered remotes. For each remote, agit
fetch
command 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.
The
remote.
<name>.skipFetchAll
configuration can be used to exclude a particular remote from getting prefetched. - 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-objects
job 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. Thegc
task 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-objects
andgc
tasks at the same time. - incremental-repack
-
The
incremental-repack
job repacks the object directory using themulti-pack-index
feature. In order to prevent race conditions with concurrent Git commands, it follows a two-step process. First, it callsgit
multi-pack-index
expire
to delete pack-files unreferenced by themulti-pack-index
file. Second, it callsgit
multi-pack-index
repack
to select several small pack-files and repack them into a bigger one, and then update themulti-pack-index
entries 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-size
option for therepack
subcommand 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-refs
task 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
run
subcommand, run maintenance tasks only if certain thresholds are met. For example, thegc
task runs when the number of loose objects exceeds the number stored in thegc.auto
config setting, or when the number of pack-files exceeds thegc.autoPackLimit
config setting. Not compatible with the--schedule
option. - --schedule
-
When combined with the
run
subcommand, run maintenance tasks only if certain time conditions are met, as specified by themaintenance.
<task>.schedule
config value for each <task>. This config value specifies a number of seconds since the last time that task ran, according to themaintenance.
<task>.lastRun
config value. The tasks that are tested are those provided by the--task=
<task> option(s) or those withmaintenance.
<task>.enabled
set 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>.enabled
configured astrue
are considered. See the TASKS section for the list of accepted <task> values. - --scheduler=auto|crontab|systemd-timer|launchctl|schtasks
-
When combined with the
start
subcommand, 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). Whenauto
is specified, the appropriate platform-specific scheduler is used; on Linux,systemd-timer
is 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. The processes are scheduled to a random minute of
the hour per client to spread out the load that multiple clients might
generate (e.g. from prefetching). 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 SCHEDULE
The 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 [email protected] [email protected] Fri 2021-04-30 00:00:00 CEST 5h 42min left Thu 2021-04-29 00:00:11 CEST 18h ago [email protected] [email protected] Mon 2021-05-03 00:00:00 CEST 3 days left Mon 2021-04-26 00:00:11 CEST 3 days ago [email protected] [email protected]
One timer is registered for each --schedule=
<frequency> option.
The definition of the systemd units can be inspected in the following files:
~/.config/systemd/user/[email protected] ~/.config/systemd/user/[email protected] ~/.config/systemd/user/timers.target.wants/[email protected] ~/.config/systemd/user/timers.target.wants/[email protected] ~/.config/systemd/user/timers.target.wants/[email protected]
git
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/[email protected]
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.plist
One 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
--auto
after doing their normal work. Defaults to true. - maintenance.autoDetach
-
Many Git commands trigger automatic maintenance after they have written data into the repository. This boolean config option controls whether this automatic maintenance shall happen in the foreground or whether the maintenance process shall detach and continue to run in the background.
If unset, the value of
gc.autoDetach
is used as a fallback. Defaults to true if both are unset, meaning that the maintenance process will detach. - 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=X
commands, provided no--task=
<task> arguments are provided. Further, if amaintenance.
<task>.schedule
config 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 thegc
task, but runs theprefetch
andcommit-graph
tasks hourly, theloose-objects
andincremental-repack
tasks daily, and thepack-refs
task weekly.
-
- maintenance.<task>.enabled
-
This boolean config option controls whether the maintenance task with name <task> is run when no
--task
option is specified togit
maintenance
run
. These config values are ignored if a--task
option exists. By default, onlymaintenance.gc.enabled
is true. - maintenance.<task>.schedule
-
This config option controls whether or not the given <task> runs during a
git
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-graph
task should be run as part ofgit
maintenance
run
--auto
. If zero, then thecommit-graph
task will not run with the--auto
option. 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-objects
task should be run as part ofgit
maintenance
run
--auto
. If zero, then theloose-objects
task will not run with the--auto
option. 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-repack
task should be run as part ofgit
maintenance
run
--auto
. If zero, then theincremental-repack
task will not run with the--auto
option. 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