git-maintenance

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



NAME
       git-maintenance - Run tasks to optimize Git repository data

SYNOPSIS
       git maintenance run [<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
       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 subcomand 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
       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 refmap is custom to avoid updating local or
           remote branches (those in refs/heads or refs/remotes). Instead, the
           remote refs are stored in refs/prefetch/<remote>/. 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.

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.

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.

GIT
       Part of the git(1) suite



Git 2.30.0                         12/28/2020                 GIT-MAINTENANCE(1)