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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:

•gc: disabled.
•commit-graph: hourly.
•prefetch: hourly.
•loose-objects: daily.
•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.

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.
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.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:
•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 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

02/23/2024 Git 2.44.0

Package information:

Package name: extra/git Version: 2.44.0-1 Upstream: https://git-scm.com/
Licenses: GPL2 Manuals: /listing/extra/git/
Table of contents
 * NAME
 * SYNOPSIS
 * DESCRIPTION
 * SUBCOMMANDS
 * TASKS
 * OPTIONS
 * TROUBLESHOOTING
 * BACKGROUND MAINTENANCE ON POSIX SYSTEMS
 * BACKGROUND MAINTENANCE ON LINUX SYSTEMD SYSTEMS
 * BACKGROUND MAINTENANCE ON MACOS SYSTEMS
 * BACKGROUND MAINTENANCE ON WINDOWS SYSTEMS
 * CONFIGURATION
 * GIT





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