GIT-PACK-OBJECTS(1) Git Manual GIT-PACK-OBJECTS(1)
NAME
git-pack-objects - Create a packed archive of objects
SYNOPSIS
git pack-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>]
[--stdout [--filter=<filter-spec>] | base-name]
[--shallow] [--keep-true-parents] [--[no-]sparse] < object-list
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 git unpack-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.
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 git rev-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.
--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. This option prevents the creation of a
bitmap index. The default is unlimited, unless the config variable
pack.packSizeLimit is set.
--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 git index-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, git
pack-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 git gc (see git-gc(1)), git repack
(see git-repack(1)) pass this option by default in modern Git when
they put objects in your repository into pack files. So does git
bundle (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>
Requires --stdout. 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. This is the default
action.
The form --missing=allow-any will allow object traversal to
continue if a missing object is encountered. 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. 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.
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).
SEE ALSO
git-rev-list(1)git-repack(1)git-prune-packed(1)
GIT
Part of the git(1) suite
Git 2.27.0 06/01/2020 GIT-PACK-OBJECTS(1)