git-commit-vandalism/Documentation/git-pack-objects.txt

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git-pack-objects(1)
===================
NAME
----
git-pack-objects - Create a packed archive of objects
SYNOPSIS
--------
pack-objects: finishing touches. This introduces --no-reuse-delta option to disable reusing of existing delta, which is a large part of the optimization introduced by this series. This may become necessary if repeated repacking makes delta chain too long. With this, the output of the command becomes identical to that of the older implementation. But the performance suffers greatly. It still allows reusing non-deltified representations; there is no point uncompressing and recompressing the whole text. It also adds a couple more statistics output, while squelching it under -q flag, which the last round forgot to do. $ time old-git-pack-objects --stdout >/dev/null <RL Generating pack... Done counting 184141 objects. Packing 184141 objects.................... real 12m8.530s user 11m1.450s sys 0m57.920s $ time git-pack-objects --stdout >/dev/null <RL Generating pack... Done counting 184141 objects. Packing 184141 objects..................... Total 184141, written 184141 (delta 138297), reused 178833 (delta 134081) real 0m59.549s user 0m56.670s sys 0m2.400s $ time git-pack-objects --stdout --no-reuse-delta >/dev/null <RL Generating pack... Done counting 184141 objects. Packing 184141 objects..................... Total 184141, written 184141 (delta 134833), reused 47904 (delta 0) real 11m13.830s user 9m45.240s sys 0m44.330s There is one remaining issue when --no-reuse-delta option is not used. It can create delta chains that are deeper than specified. A<--B<--C<--D E F G Suppose we have a delta chain A to D (A is stored in full either in a pack or as a loose object. B is depth1 delta relative to A, C is depth2 delta relative to B...) with loose objects E, F, G. And we are going to pack all of them. B, C and D are left as delta against A, B and C respectively. So A, E, F, and G are examined for deltification, and let's say we decided to keep E expanded, and store the rest as deltas like this: E<--F<--G<--A Oops. We ended up making D a bit too deep, didn't we? B, C and D form a chain on top of A! This is because we did not know what the final depth of A would be, when we checked objects and decided to keep the existing delta. Unfortunately, deferring the decision until just before the deltification is not an option. To be able to make B, C, and D candidates for deltification with the rest, we need to know the type and final unexpanded size of them, but the major part of the optimization comes from the fact that we do not read the delta data to do so -- getting the final size is quite an expensive operation. To prevent this from happening, we should keep A from being deltified. But how would we tell that, cheaply? To do this most precisely, after check_object() runs, each object that is used as the base object of some existing delta needs to be marked with the maximum depth of the objects we decided to keep deltified (in this case, D is depth 3 relative to A, so if no other delta chain that is longer than 3 based on A exists, mark A with 3). Then when attempting to deltify A, we would take that number into account to see if the final delta chain that leads to D becomes too deep. However, this is a bit cumbersome to compute, so we would cheat and reduce the maximum depth for A arbitrarily to depth/4 in this implementation. Signed-off-by: Junio C Hamano <junkio@cox.net>
2006-02-16 20:55:51 +01:00
[verse]
'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]] [--stdout | base-name]
[--keep-true-parents] < object-list
DESCRIPTION
-----------
Reads list of objects from the standard input, and writes a packed
archive with specified base-name, or 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 a pair of files (.pack and .idx), using
<base-name> to determine the name of the created file.
When this option is used, the two files 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.
--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.
--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, which is the
default.
--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.
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.
--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.
pack-objects: finishing touches. This introduces --no-reuse-delta option to disable reusing of existing delta, which is a large part of the optimization introduced by this series. This may become necessary if repeated repacking makes delta chain too long. With this, the output of the command becomes identical to that of the older implementation. But the performance suffers greatly. It still allows reusing non-deltified representations; there is no point uncompressing and recompressing the whole text. It also adds a couple more statistics output, while squelching it under -q flag, which the last round forgot to do. $ time old-git-pack-objects --stdout >/dev/null <RL Generating pack... Done counting 184141 objects. Packing 184141 objects.................... real 12m8.530s user 11m1.450s sys 0m57.920s $ time git-pack-objects --stdout >/dev/null <RL Generating pack... Done counting 184141 objects. Packing 184141 objects..................... Total 184141, written 184141 (delta 138297), reused 178833 (delta 134081) real 0m59.549s user 0m56.670s sys 0m2.400s $ time git-pack-objects --stdout --no-reuse-delta >/dev/null <RL Generating pack... Done counting 184141 objects. Packing 184141 objects..................... Total 184141, written 184141 (delta 134833), reused 47904 (delta 0) real 11m13.830s user 9m45.240s sys 0m44.330s There is one remaining issue when --no-reuse-delta option is not used. It can create delta chains that are deeper than specified. A<--B<--C<--D E F G Suppose we have a delta chain A to D (A is stored in full either in a pack or as a loose object. B is depth1 delta relative to A, C is depth2 delta relative to B...) with loose objects E, F, G. And we are going to pack all of them. B, C and D are left as delta against A, B and C respectively. So A, E, F, and G are examined for deltification, and let's say we decided to keep E expanded, and store the rest as deltas like this: E<--F<--G<--A Oops. We ended up making D a bit too deep, didn't we? B, C and D form a chain on top of A! This is because we did not know what the final depth of A would be, when we checked objects and decided to keep the existing delta. Unfortunately, deferring the decision until just before the deltification is not an option. To be able to make B, C, and D candidates for deltification with the rest, we need to know the type and final unexpanded size of them, but the major part of the optimization comes from the fact that we do not read the delta data to do so -- getting the final size is quite an expensive operation. To prevent this from happening, we should keep A from being deltified. But how would we tell that, cheaply? To do this most precisely, after check_object() runs, each object that is used as the base object of some existing delta needs to be marked with the maximum depth of the objects we decided to keep deltified (in this case, D is depth 3 relative to A, so if no other delta chain that is longer than 3 based on A exists, mark A with 3). Then when attempting to deltify A, we would take that number into account to see if the final delta chain that leads to D becomes too deep. However, this is a bit cumbersome to compute, so we would cheat and reduce the maximum depth for A arbitrarily to depth/4 in this implementation. Signed-off-by: Junio C Hamano <junkio@cox.net>
2006-02-16 20:55:51 +01:00
-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.
Custom compression levels for objects and packs Add config variables pack.compression and core.loosecompression , and switch --compression=level to pack-objects. Loose objects will be compressed using core.loosecompression if set, else core.compression if set, else Z_BEST_SPEED. Packed objects will be compressed using --compression=level if seen, else pack.compression if set, else core.compression if set, else Z_DEFAULT_COMPRESSION. This is the "pack compression level". Loose objects added to a pack undeltified will be recompressed to the pack compression level if it is unequal to the current loose compression level by the preceding rules, or if the loose object was written while core.legacyheaders = true. Newly deltified loose objects are always compressed to the current pack compression level. Previously packed objects added to a pack are recompressed to the current pack compression level exactly when their deltification status changes, since the previous pack data cannot be reused. In either case, the --no-reuse-object switch from the first patch below will always force recompression to the current pack compression level, instead of assuming the pack compression level hasn't changed and pack data can be reused when possible. This applies on top of the following patches from Nicolas Pitre: [PATCH] allow for undeltified objects not to be reused [PATCH] make "repack -f" imply "pack-objects --no-reuse-object" Signed-off-by: Dana L. How <danahow@gmail.com> Signed-off-by: Junio C Hamano <junkio@cox.net>
2007-05-09 22:56:50 +02:00
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>::
Custom compression levels for objects and packs Add config variables pack.compression and core.loosecompression , and switch --compression=level to pack-objects. Loose objects will be compressed using core.loosecompression if set, else core.compression if set, else Z_BEST_SPEED. Packed objects will be compressed using --compression=level if seen, else pack.compression if set, else core.compression if set, else Z_DEFAULT_COMPRESSION. This is the "pack compression level". Loose objects added to a pack undeltified will be recompressed to the pack compression level if it is unequal to the current loose compression level by the preceding rules, or if the loose object was written while core.legacyheaders = true. Newly deltified loose objects are always compressed to the current pack compression level. Previously packed objects added to a pack are recompressed to the current pack compression level exactly when their deltification status changes, since the previous pack data cannot be reused. In either case, the --no-reuse-object switch from the first patch below will always force recompression to the current pack compression level, instead of assuming the pack compression level hasn't changed and pack data can be reused when possible. This applies on top of the following patches from Nicolas Pitre: [PATCH] allow for undeltified objects not to be reused [PATCH] make "repack -f" imply "pack-objects --no-reuse-object" Signed-off-by: Dana L. How <danahow@gmail.com> Signed-off-by: Junio C Hamano <junkio@cox.net>
2007-05-09 22:56:50 +02:00
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.
Custom compression levels for objects and packs Add config variables pack.compression and core.loosecompression , and switch --compression=level to pack-objects. Loose objects will be compressed using core.loosecompression if set, else core.compression if set, else Z_BEST_SPEED. Packed objects will be compressed using --compression=level if seen, else pack.compression if set, else core.compression if set, else Z_DEFAULT_COMPRESSION. This is the "pack compression level". Loose objects added to a pack undeltified will be recompressed to the pack compression level if it is unequal to the current loose compression level by the preceding rules, or if the loose object was written while core.legacyheaders = true. Newly deltified loose objects are always compressed to the current pack compression level. Previously packed objects added to a pack are recompressed to the current pack compression level exactly when their deltification status changes, since the previous pack data cannot be reused. In either case, the --no-reuse-object switch from the first patch below will always force recompression to the current pack compression level, instead of assuming the pack compression level hasn't changed and pack data can be reused when possible. This applies on top of the following patches from Nicolas Pitre: [PATCH] allow for undeltified objects not to be reused [PATCH] make "repack -f" imply "pack-objects --no-reuse-object" Signed-off-by: Dana L. How <danahow@gmail.com> Signed-off-by: Junio C Hamano <junkio@cox.net>
2007-05-09 22:56:50 +02:00
--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 linkgit:git-index-pack[1]) to restore the self-contained property.
--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 linkgit:git-gc[1]),
`git repack` (see linkgit: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 linkgit: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.
SEE ALSO
--------
linkgit:git-rev-list[1]
linkgit:git-repack[1]
linkgit:git-prune-packed[1]
GIT
---
Part of the linkgit:git[1] suite