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. With prefetch task, however, the objects necessary to complete
a later real fetch would already be obtained, so the real fetch would
go 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:
o none: This default setting implies no task 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 2.39.0 12/12/2022 git-maintenance(1)
git 2.39.0 - Generated Tue Dec 13 08:51:03 CST 2022