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GIT-MAINTENANCE(1) Git Manual GIT-MAINTENANCE(1)
git-maintenance - Run tasks to optimize Git repository data
git maintenance run [<options>]
git maintenance start [--scheduler=<scheduler>]
git maintenance (stop|register|unregister) [<options>]
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.
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.
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.
--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.
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.
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.
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).
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.
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.
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.
Part of the git(1) suite
This page is part of the git (Git distributed version control
system) project. Information about the project can be found at
⟨http://git-scm.com/⟩. If you have a bug report for this manual
page, see ⟨http://git-scm.com/community⟩. This page was obtained
from the project's upstream Git repository
⟨https://github.com/git/git.git⟩ on 2024-06-14. (At that time,
the date of the most recent commit that was found in the
repository was 2024-06-12.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
Git 2.45.2.492.gd63586 2024-06-12 GIT-MAINTENANCE(1)
Pages that refer to this page: git(1), git-clone(1), git-fetch(1), git-pull(1), scalar(1)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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