git-maintenance - Run tasks to optimize Git repository data
git maintenance run [<options>] git maintenance start [--scheduler=<scheduler>] git maintenance (stop|register|unregister)
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)
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 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.
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.
GIT
Part of the git(1) suite
Git 2.36.0 04/17/2022 GIT-MAINTENANCE(1)