GIT-MAINTENANCE(1) Git Manual GIT-MAINTENANCE(1)

NAME

git-maintenance - Run tasks to optimize Git repository data

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 which maintenance.<task>.enabled
config options are true. By default, only maintenance.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 run git 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 for
maintenance.<task>.schedule. The tasks that are enabled are safe
for running in the background without disrupting foreground
processes.

The register subcommand will also set the maintenance.strategy
config value to incremental, if this value is not previously set.
The incremental strategy uses the following schedule for each
maintenance task:

+o gc: disabled.

+o commit-graph: hourly.

+o prefetch: hourly.

+o loose-objects: daily.

+o incremental-repack: daily.

git maintenance register will also disable foreground maintenance
by setting maintenance.auto = false in the current repository.
This config setting will remain after a git 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 the commit-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
previous commit-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, a git fetch
command is run. The configured refspec is modified to place all
requested refs within refs/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. The gc 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 the loose-objects and gc tasks at the same time.

incremental-repack
The incremental-repack job repacks the object directory using the
multi-pack-index feature. In order to prevent race conditions
with concurrent Git commands, it follows a two-step process.
First, it calls git multi-pack-index expire to delete pack-files
unreferenced by the multi-pack-index file. Second, it calls git
multi-pack-index repack to select several small pack-files and
repack them into a bigger one, and then update the
multi-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 of git 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 the repack 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, the gc task runs when
the number of loose objects exceeds the number stored in the
gc.auto config setting, or when the number of pack-files exceeds
the gc.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 the
maintenance.<task>.schedule config value for each <task>. This
config value specifies a number of seconds since the last time
that task ran, according to the maintenance.<task>.lastRun config
value. The tasks that are tested are those provided by the
--task=<task> option(s) or those with maintenance.<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 with
maintenance.<task>.enabled configured as true 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 of git
maintenance run. Possible values for <scheduler> are auto,
crontab (POSIX), systemd-timer (Linux), launchctl (macOS), and
schtasks (Windows). When auto is specified, the appropriate
platform-specific scheduler is used; on Linux, systemd-timer is
used if available, otherwise crontab. Default is auto.

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 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.service

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/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.timer

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/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.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 a maintenance.<task>.schedule config value
is set, then that value is used instead of the one provided by
maintenance.strategy. The possible strategy strings are:

+o none: This default setting implies no tasks are run at any
schedule.

+o incremental: This setting optimizes for performing small
maintenance activities that do not delete any data. This does
not schedule the gc task, but runs the prefetch and
commit-graph tasks hourly, the loose-objects and
incremental-repack tasks daily, and the pack-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 to git
maintenance run. These config values are ignored if a --task
option exists. By default, only maintenance.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 of git maintenance run --auto. If
zero, then the commit-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 of maintenance.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 of git maintenance run --auto. If
zero, then the loose-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 of
maintenance.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 of git maintenance
run --auto. If zero, then the incremental-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 of
maintenance.incremental-repack.auto. The default value is 10.

GIT

Part of the git(1) suite

Git 2.48.1 2025-01-13 GIT-MAINTENANCE(1)