git-maintenance(1) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | SUBCOMMANDS | TASKS | OPTIONS | TROUBLESHOOTING | BACKGROUND MAINTENANCE ON POSIX SYSTEMS | BACKGROUND MAINTENANCE ON MACOS SYSTEMS | BACKGROUND MAINTENANCE ON WINDOWS SYSTEMS | GIT | COLOPHON

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

NAME         top

       git-maintenance - Run tasks to optimize Git repository data

SYNOPSIS         top

       git maintenance run [<options>]

DESCRIPTION         top

       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         top

       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:

           •   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.

       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.

       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         top

       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         top

       --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.

TROUBLESHOOTING         top

       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         top

       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 MACOS SYSTEMS         top

       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         top

       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         top

       Part of the git(1) suite

COLOPHON         top

       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 2021-08-27.  (At that time,
       the date of the most recent commit that was found in the
       repository was 2021-08-24.)  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
       man-pages@man7.org

Git 2.33.0.69.gc420321         08/27/2021             GIT-MAINTENANCE(1)

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