git-pack-objects - Create a packed archive of objects

Configuration

       Various configuration variables affect packing, see git-config(1) (search for "pack" and "delta").

       Notably, delta compression is not used on objects larger than the core.bigFileThreshold configuration
       variable and on files with the attribute delta set to false.

Delta Islands

When possible, pack-objects tries to reuse existing on-disk deltas to avoid having to search for new ones
on the fly. This is an important optimization for serving fetches, because it means the server can avoid
inflating most objects at all and just send the bytes directly from disk. This optimization can’t work
when an object is stored as a delta against a base which the receiver does not have (and which we are not
already sending). In that case the server "breaks" the delta and has to find a new one, which has a high
CPU cost. Therefore it’s important for performance that the set of objects in on-disk delta relationships
match what a client would fetch.

In a normal repository, this tends to work automatically. The objects are mostly reachable from the
branches and tags, and that’s what clients fetch. Any deltas we find on the server are likely to be
between objects the client has or will have.

But in some repository setups, you may have several related but separate groups of ref tips, with clients
tending to fetch those groups independently. For example, imagine that you are hosting several "forks" of
a repository in a single shared object store, and letting clients view them as separate repositories
through GIT_NAMESPACE or separate repos using the alternates mechanism. A naive repack may find that the
optimal delta for an object is against a base that is only found in another fork. But when a client
fetches, they will not have the base object, and we’ll have to find a new delta on the fly.

A similar situation may exist if you have many refs outside of refs/heads/ and refs/tags/ that point to
related objects (e.g., refs/pull or refs/changes used by some hosting providers). By default, clients
fetch only heads and tags, and deltas against objects found only in those other groups cannot be sent
as-is.

Delta islands solve this problem by allowing you to group your refs into distinct "islands". Pack-objects
computes which objects are reachable from which islands, and refuses to make a delta from an object A
against a base which is not present in all of A's islands. This results in slightly larger packs (because
we miss some delta opportunities), but guarantees that a fetch of one island will not have to recompute
deltas on the fly due to crossing island boundaries.

When repacking with delta islands the delta window tends to get clogged with candidates that are
forbidden by the config. Repacking with a big --window helps (and doesn’t take as long as it otherwise
might because we can reject some object pairs based on islands before doing any computation on the
content).

Islands are configured via the pack.island option, which can be specified multiple times. Each value is a
left-anchored regular expressions matching refnames. For example:

[pack]
island = refs/heads/
island = refs/tags/

puts heads and tags into an island (whose name is the empty string; see below for more on naming). Any
refs which do not match those regular expressions (e.g., refs/pull/123) is not in any island. Any object
which is reachable only from refs/pull/ (but not heads or tags) is therefore not a candidate to be used
as a base for refs/heads/.

Refs are grouped into islands based on their "names", and two regexes that produce the same name are
considered to be in the same island. The names are computed from the regexes by concatenating any capture
groups from the regex, with a - dash in between. (And if there are no capture groups, then the name is
the empty string, as in the above example.) This allows you to create arbitrary numbers of islands. Only
up to 14 such capture groups are supported though.

For example, imagine you store the refs for each fork in refs/virtual/ID, where ID is a numeric
identifier. You might then configure:

[pack]
island = refs/virtual/([0-9]+)/heads/
island = refs/virtual/([0-9]+)/tags/
island = refs/virtual/([0-9]+)/(pull)/

That puts the heads and tags for each fork in their own island (named "1234" or similar), and the pull
refs for each go into their own "1234-pull".

Note that we pick a single island for each regex to go into, using "last one wins" ordering (which allows
repo-specific config to take precedence over user-wide config, and so forth).

Description

       Reads list of objects from the standard input, and writes either one or more packed archives with the
       specified base-name to disk, or a packed archive to the standard output.

       A packed archive is an efficient way to transfer a set of objects between two repositories as well as an
       access efficient archival format. In a packed archive, an object is either stored as a compressed whole
       or as a difference from some other object. The latter is often called a delta.

       The packed archive format (.pack) is designed to be self-contained so that it can be unpacked without any
       further information. Therefore, each object that a delta depends upon must be present within the pack.

       A pack index file (.idx) is generated for fast, random access to the objects in the pack. Placing both
       the index file (.idx) and the packed archive (.pack) in the pack/ subdirectory of $GIT_OBJECT_DIRECTORY
       (or any of the directories on $GIT_ALTERNATE_OBJECT_DIRECTORIES) enables Git to read from the pack
       archive.

       The gitunpack-objects command can read the packed archive and expand the objects contained in the pack
       into "one-file one-object" format; this is typically done by the smart-pull commands when a pack is
       created on-the-fly for efficient network transport by their peers.

Git

       Part of the git(1) suite

Git 2.48.1                                         07/02/2025                                GIT-PACK-OBJECTS(1)

Name

       git-pack-objects - Create a packed archive of objects

Options

base-name
Write into pairs of files (.pack and .idx), using <base-name> to determine the name of the created
file. When this option is used, the two files in a pair are written in <base-name>-<SHA-1>.{pack,idx}
files. <SHA-1> is a hash based on the pack content and is written to the standard output of the
command.

--stdout
Write the pack contents (what would have been written to .pack file) out to the standard output.

--revs
Read the revision arguments from the standard input, instead of individual object names. The revision
arguments are processed the same way as gitrev-list with the --objects flag uses its commit
arguments to build the list of objects it outputs. The objects on the resulting list are packed.
Besides revisions, --not or --shallow<SHA-1> lines are also accepted.

--unpacked
This implies --revs. When processing the list of revision arguments read from the standard input,
limit the objects packed to those that are not already packed.

--all
This implies --revs. In addition to the list of revision arguments read from the standard input,
pretend as if all refs under refs/ are specified to be included.

--include-tag
Include unasked-for annotated tags if the object they reference was included in the resulting
packfile. This can be useful to send new tags to native Git clients.

--stdin-packs
Read the basenames of packfiles (e.g., pack-1234abcd.pack) from the standard input, instead of object
names or revision arguments. The resulting pack contains all objects listed in the included packs
(those not beginning with ^), excluding any objects listed in the excluded packs (beginning with ^).

Incompatible with --revs, or options that imply --revs (such as --all), with the exception of
--unpacked, which is compatible.

--cruft
Packs unreachable objects into a separate "cruft" pack, denoted by the existence of a .mtimes file.
Typically used by gitrepack--cruft. Callers provide a list of pack names and indicate which packs
will remain in the repository, along with which packs will be deleted (indicated by the - prefix).
The contents of the cruft pack are all objects not contained in the surviving packs which have not
exceeded the grace period (see --cruft-expiration below), or which have exceeded the grace period,
but are reachable from an other object which hasn’t.

When the input lists a pack containing all reachable objects (and lists all other packs as pending
deletion), the corresponding cruft pack will contain all unreachable objects (with mtime newer than
the --cruft-expiration) along with any unreachable objects whose mtime is older than the
--cruft-expiration, but are reachable from an unreachable object whose mtime is newer than the
--cruft-expiration).

Incompatible with --unpack-unreachable, --keep-unreachable, --pack-loose-unreachable, --stdin-packs,
as well as any other options which imply --revs.

--cruft-expiration=<approxidate>
If specified, objects are eliminated from the cruft pack if they have an mtime older than
<approxidate>. If unspecified (and given --cruft), then no objects are eliminated.

--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.

--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.

--max-pack-size=<n>
In unusual scenarios, you may not be able to create files larger than a certain size on your
filesystem, and this option can be used to tell the command to split the output packfile into
multiple independent packfiles, each not larger than the given size. The size can be suffixed with
"k", "m", or "g". The minimum size allowed is limited to 1 MiB. 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.

--honor-pack-keep
This flag causes an object already in a local pack that has a .keep file to be ignored, even if it
would have otherwise been packed.

--keep-pack=<pack-name>
This flag causes an object already in the given pack to be ignored, even if it would have otherwise
been packed. <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.

--incremental
This flag causes an object already in a pack to be ignored even if it would have otherwise been
packed.

--local
This flag causes an object that is borrowed from an alternate object store to be ignored even if it
would have otherwise been packed.

--non-empty
Only create a packed archive if it would contain at least one object.

--progress
Progress status is reported on the standard error stream by default when it is attached to a
terminal, unless -q is specified. This flag forces progress status even if the standard error stream
is not directed to a terminal.

--all-progress
When --stdout is specified then progress report is displayed during the object count and compression
phases but inhibited during the write-out phase. The reason is that in some cases the output stream
is directly linked to another command which may wish to display progress status of its own as it
processes incoming pack data. This flag is like --progress except that it forces progress report for
the write-out phase as well even if --stdout is used.

--all-progress-implied
This is used to imply --all-progress whenever progress display is activated. Unlike --all-progress
this flag doesn’t actually force any progress display by itself.

-q
This flag makes the command not to report its progress on the standard error stream.

--no-reuse-delta
When creating a packed archive in a repository that has existing packs, the command reuses existing
deltas. This sometimes results in a slightly suboptimal pack. This flag tells the command not to
reuse existing deltas but compute them from scratch.

--no-reuse-object
This flag tells the command not to reuse existing object data at all, including non deltified object,
forcing recompression of everything. This implies --no-reuse-delta. Useful only in the obscure case
where wholesale enforcement of a different compression level on the packed data is desired.

--compression=<n>
Specifies compression level for newly-compressed data in the generated pack. If not specified, pack
compression level is determined first by pack.compression, then by core.compression, and defaults to
-1, the zlib default, if neither is set. Add --no-reuse-object if you want to force a uniform
compression level on all data no matter the source.

--[no-]sparse
Toggle the "sparse" algorithm to determine which objects to include in the pack, when combined with
the "--revs" option. This algorithm only walks trees that appear in paths that introduce new objects.
This can have significant performance benefits when computing a pack to send a small change. However,
it is possible that extra objects are added to the pack-file if the included commits contain certain
types of direct renames. If this option is not included, it defaults to the value of pack.useSparse,
which is true unless otherwise specified.

--thin
Create a "thin" pack by omitting the common objects between a sender and a receiver in order to
reduce network transfer. This option only makes sense in conjunction with --stdout.

Note: A thin pack violates the packed archive format by omitting required objects and is thus
unusable by Git without making it self-contained. Use gitindex-pack--fix-thin (see git-index-pack(1)) to restore the self-contained property.

--shallow
Optimize a pack that will be provided to a client with a shallow repository. This option, combined
with --thin, can result in a smaller pack at the cost of speed.

--delta-base-offset
A packed archive can express the base object of a delta as either a 20-byte object name or as an
offset in the stream, but ancient versions of Git don’t understand the latter. By default, gitpack-objects only uses the former format for better compatibility. This option allows the command to
use the latter format for compactness. Depending on the average delta chain length, this option
typically shrinks the resulting packfile by 3-5 per-cent.

Note: Porcelain commands such as gitgc (see git-gc(1)), gitrepack (see git-repack(1)) pass this
option by default in modern Git when they put objects in your repository into pack files. So does gitbundle (see git-bundle(1)) when it creates a bundle.

--threads=<n>
Specifies the number of threads to spawn when searching for best delta matches. This requires that
pack-objects be compiled with pthreads otherwise this option is ignored with a warning. This is meant
to reduce packing time on multiprocessor machines. The required amount of memory for the delta search
window is however multiplied by the number of threads. Specifying 0 will cause Git to auto-detect the
number of CPU’s and set the number of threads accordingly.

--index-version=<version>[,<offset>]
This is intended to be used by the test suite only. It allows to force the version for the generated
pack index, and to force 64-bit index entries on objects located above the given offset.

--keep-true-parents
With this option, parents that are hidden by grafts are packed nevertheless.

--filter=<filter-spec>
Omits certain objects (usually blobs) from the resulting packfile. See git-rev-list(1) for valid
<filter-spec> forms.

--no-filter
Turns off any previous --filter= argument.

--missing=<missing-action>
A debug option to help with future "partial clone" development. This option specifies how missing
objects are handled.

The form --missing=error requests that pack-objects stop with an error if a missing object is
encountered. If the repository is a partial clone, an attempt to fetch missing objects will be made
before declaring them missing. This is the default action.

The form --missing=allow-any will allow object traversal to continue if a missing object is
encountered. No fetch of a missing object will occur. Missing objects will silently be omitted from
the results.

The form --missing=allow-promisor is like allow-any, but will only allow object traversal to continue
for EXPECTED promisor missing objects. No fetch of a missing object will occur. An unexpected missing
object will raise an error.

--exclude-promisor-objects
Omit objects that are known to be in the promisor remote. (This option has the purpose of operating
only on locally created objects, so that when we repack, we still maintain a distinction between
locally created objects [without .promisor] and objects from the promisor remote [with .promisor].)
This is used with partial clone.

--keep-unreachable
Objects unreachable from the refs in packs named with --unpacked= option are added to the resulting
pack, in addition to the reachable objects that are not in packs marked with *.keep files. This
implies --revs.

--pack-loose-unreachable
Pack unreachable loose objects (and their loose counterparts removed). This implies --revs.

--unpack-unreachable
Keep unreachable objects in loose form. This implies --revs.

--delta-islands
Restrict delta matches based on "islands". See DELTA ISLANDS below.

Synopsis

gitpack-objects [-q | --progress | --all-progress] [--all-progress-implied]
               [--no-reuse-delta] [--delta-base-offset] [--non-empty]
               [--local] [--incremental] [--window=<n>] [--depth=<n>]
               [--revs [--unpacked | --all]] [--keep-pack=<pack-name>]
               [--cruft] [--cruft-expiration=<time>]
               [--stdout [--filter=<filter-spec>] | <base-name>]
               [--shallow] [--keep-true-parents] [--[no-]sparse] < <object-list>