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git-commit-vandalism/Documentation/git-repack.txt
Taylor Blau 6d08b9d4ca builtin/repack.c: make largest pack preferred 
When repacking into a geometric series and writing a multi-pack bitmap,
it is beneficial to have the largest resulting pack be the preferred
object source in the bitmap's MIDX, since selecting the large packs can
lead to fewer broken delta chains and better compression.

Teach 'git repack' to identify this pack and pass it to the MIDX write
machinery in order to mark it as preferred.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2021-09-28 21:20:56 -07:00

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git-repack(1)
=============
NAME
----
git-repack - Pack unpacked objects in a repository
SYNOPSIS
--------
[verse]
'git repack' [-a] [-A] [-d] [-f] [-F] [-l] [-n] [-q] [-b] [-m] [--window=<n>] [--depth=<n>] [--threads=<n>] [--keep-pack=<pack-name>] [--write-midx]
DESCRIPTION
-----------
This command is used to combine all objects that do not currently
reside in a "pack", into a pack. It can also be used to re-organize
existing packs into a single, more efficient pack.
A pack is a collection of objects, individually compressed, with
delta compression applied, stored in a single file, with an
associated index file.
Packs are used to reduce the load on mirror systems, backup
engines, disk storage, etc.
OPTIONS
-------
-a::
Instead of incrementally packing the unpacked objects,
pack everything referenced into a single pack.
Especially useful when packing a repository that is used
for private development. Use
with `-d`. This will clean up the objects that `git prune`
leaves behind, but `git fsck --full --dangling` shows as
dangling.
+
Note that users fetching over dumb protocols will have to fetch the
whole new pack in order to get any contained object, no matter how many
other objects in that pack they already have locally.
+
Promisor packfiles are repacked separately: if there are packfiles that
have an associated ".promisor" file, these packfiles will be repacked
into another separate pack, and an empty ".promisor" file corresponding
to the new separate pack will be written.
-A::
Same as `-a`, unless `-d` is used. Then any unreachable
objects in a previous pack become loose, unpacked objects,
instead of being left in the old pack. Unreachable objects
are never intentionally added to a pack, even when repacking.
This option prevents unreachable objects from being immediately
deleted by way of being left in the old pack and then
removed. Instead, the loose unreachable objects
will be pruned according to normal expiry rules
with the next 'git gc' invocation. See linkgit:git-gc[1].
-d::
After packing, if the newly created packs make some
existing packs redundant, remove the redundant packs.
Also run 'git prune-packed' to remove redundant
loose object files.
-l::
Pass the `--local` option to 'git pack-objects'. See
linkgit:git-pack-objects[1].
-f::
Pass the `--no-reuse-delta` option to `git-pack-objects`, see
linkgit:git-pack-objects[1].
-F::
Pass the `--no-reuse-object` option to `git-pack-objects`, see
linkgit:git-pack-objects[1].
-q::
Pass the `-q` option to 'git pack-objects'. See
linkgit:git-pack-objects[1].
-n::
Do not update the server information with
'git update-server-info'. This option skips
updating local catalog files needed to publish
this repository (or a direct copy of it)
over HTTP or FTP. See linkgit:git-update-server-info[1].
--window=<n>::
--depth=<n>::
These two options affect how the objects contained in the pack are
stored using delta compression. The objects are first internally
sorted by type, size and optionally names and compared against the
other objects within `--window` to see if using delta compression saves
space. `--depth` limits the maximum delta depth; making it too deep
affects the performance on the unpacker side, because delta data needs
to be applied that many times to get to the necessary object.
+
The default value for --window is 10 and --depth is 50. The maximum
depth is 4095.
--threads=<n>::
This option is passed through to `git pack-objects`.
--window-memory=<n>::
This option provides an additional limit on top of `--window`;
the window size will dynamically scale down so as to not take
up more than '<n>' bytes in memory. This is useful in
repositories with a mix of large and small objects to not run
out of memory with a large window, but still be able to take
advantage of the large window for the smaller objects. The
size can be suffixed with "k", "m", or "g".
`--window-memory=0` makes memory usage unlimited. The default
is taken from the `pack.windowMemory` configuration variable.
Note that the actual memory usage will be the limit multiplied
by the number of threads used by linkgit:git-pack-objects[1].
--max-pack-size=<n>::
Maximum size of each output pack file. The size can be suffixed with
"k", "m", or "g". The minimum size allowed is limited to 1 MiB.
If specified, multiple packfiles may be created, which also
prevents the creation of a bitmap index.
The default is unlimited, unless the config variable
`pack.packSizeLimit` is set. Note that this option may result in
a larger and slower repository; see the discussion in
`pack.packSizeLimit`.
-b::
--write-bitmap-index::
Write a reachability bitmap index as part of the repack. This
only makes sense when used with `-a`, `-A` or `-m`, as the bitmaps
must be able to refer to all reachable objects. This option
overrides the setting of `repack.writeBitmaps`. This option
has no effect if multiple packfiles are created, unless writing a
MIDX (in which case a multi-pack bitmap is created).
--pack-kept-objects::
Include objects in `.keep` files when repacking. Note that we
still do not delete `.keep` packs after `pack-objects` finishes.
This means that we may duplicate objects, but this makes the
option safe to use when there are concurrent pushes or fetches.
This option is generally only useful if you are writing bitmaps
with `-b` or `repack.writeBitmaps`, as it ensures that the
bitmapped packfile has the necessary objects.
--keep-pack=<pack-name>::
Exclude the given pack from repacking. This is the equivalent
of having `.keep` file on the pack. `<pack-name>` is the
pack file name without leading directory (e.g. `pack-123.pack`).
The option could be specified multiple times to keep multiple
packs.
--unpack-unreachable=<when>::
When loosening unreachable objects, do not bother loosening any
objects older than `<when>`. This can be used to optimize out
the write of any objects that would be immediately pruned by
a follow-up `git prune`.
-k::
--keep-unreachable::
When used with `-ad`, any unreachable objects from existing
packs will be appended to the end of the packfile instead of
being removed. In addition, any unreachable loose objects will
be packed (and their loose counterparts removed).
-i::
--delta-islands::
Pass the `--delta-islands` option to `git-pack-objects`, see
linkgit:git-pack-objects[1].
-g=<factor>::
--geometric=<factor>::
Arrange resulting pack structure so that each successive pack
contains at least `<factor>` times the number of objects as the
next-largest pack.
+
`git repack` ensures this by determining a "cut" of packfiles that need
to be repacked into one in order to ensure a geometric progression. It
picks the smallest set of packfiles such that as many of the larger
packfiles (by count of objects contained in that pack) may be left
intact.
+
Unlike other repack modes, the set of objects to pack is determined
uniquely by the set of packs being "rolled-up"; in other words, the
packs determined to need to be combined in order to restore a geometric
progression.
+
When `--unpacked` is specified, loose objects are implicitly included in
this "roll-up", without respect to their reachability. This is subject
to change in the future. This option (implying a drastically different
repack mode) is not guaranteed to work with all other combinations of
option to `git repack`.
+
When writing a multi-pack bitmap, `git repack` selects the largest resulting
pack as the preferred pack for object selection by the MIDX (see
linkgit:git-multi-pack-index[1]).
-m::
--write-midx::
Write a multi-pack index (see linkgit:git-multi-pack-index[1])
containing the non-redundant packs.
CONFIGURATION
-------------
Various configuration variables affect packing, see
linkgit:git-config[1] (search for "pack" and "delta").
By default, the command passes `--delta-base-offset` option to
'git pack-objects'; this typically results in slightly smaller packs,
but the generated packs are incompatible with versions of Git older than
version 1.4.4. If you need to share your repository with such ancient Git
versions, either directly or via the dumb http protocol, then you
need to set the configuration variable `repack.UseDeltaBaseOffset` to
"false" and repack. Access from old Git versions over the native protocol
is unaffected by this option as the conversion is performed on the fly
as needed in that case.
Delta compression is not used on objects larger than the
`core.bigFileThreshold` configuration variable and on files with the
attribute `delta` set to false.
SEE ALSO
--------
linkgit:git-pack-objects[1]
linkgit:git-prune-packed[1]
GIT
---
Part of the linkgit:git[1] suite
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