git-maintenance - Run tasks to optimize Git repository data
'git maintenance' run [<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
The `git maintenance` command provides flexibility for how to optimize the
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`
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.
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
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 bunch of remote-tracking branches without
any object transfer.
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
linkgit:git-gc for more details on garbage collection in Git.
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
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
linkgit:git-multi-pack-index. The default batch-size is zero,
which is a special case that attempts to repack all pack-files
into a single pack-file.
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.
Do not report progress or other information over `stderr`.
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.
Part of the linkgit:git suite