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Often it is useful to both:
- have relatively few packfiles in a repository, and
- avoid having so few packfiles in a repository that we repack its
entire contents regularly
This patch implements a '--geometric=<n>' option in 'git repack'. This
allows the caller to specify that they would like each pack to be at
least a factor times as large as the previous largest pack (by object
count).
Concretely, say that a repository has 'n' packfiles, labeled P1, P2,
..., up to Pn. Each packfile has an object count equal to 'objects(Pn)'.
With a geometric factor of 'r', it should be that:
objects(Pi) > r*objects(P(i-1))
for all i in [1, n], where the packs are sorted by
objects(P1) <= objects(P2) <= ... <= objects(Pn).
Since finding a true optimal repacking is NP-hard, we approximate it
along two directions:
1. We assume that there is a cutoff of packs _before starting the
repack_ where everything to the right of that cut-off already forms
a geometric progression (or no cutoff exists and everything must be
repacked).
2. We assume that everything smaller than the cutoff count must be
repacked. This forms our base assumption, but it can also cause
even the "heavy" packs to get repacked, for e.g., if we have 6
packs containing the following number of objects:
1, 1, 1, 2, 4, 32
then we would place the cutoff between '1, 1' and '1, 2, 4, 32',
rolling up the first two packs into a pack with 2 objects. That
breaks our progression and leaves us:
2, 1, 2, 4, 32
^
(where the '^' indicates the position of our split). To restore a
progression, we move the split forward (towards larger packs)
joining each pack into our new pack until a geometric progression
is restored. Here, that looks like:
2, 1, 2, 4, 32 ~> 3, 2, 4, 32 ~> 5, 4, 32 ~> ... ~> 9, 32
^ ^ ^ ^
This has the advantage of not repacking the heavy-side of packs too
often while also only creating one new pack at a time. Another wrinkle
is that we assume that loose, indexed, and reflog'd objects are
insignificant, and lump them into any new pack that we create. This can
lead to non-idempotent results.
Suggested-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
212 lines
7.8 KiB
Plaintext
212 lines
7.8 KiB
Plaintext
git-repack(1)
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=============
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NAME
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----
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git-repack - Pack unpacked objects in a repository
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SYNOPSIS
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--------
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[verse]
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'git repack' [-a] [-A] [-d] [-f] [-F] [-l] [-n] [-q] [-b] [--window=<n>] [--depth=<n>] [--threads=<n>] [--keep-pack=<pack-name>]
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DESCRIPTION
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-----------
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This command is used to combine all objects that do not currently
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reside in a "pack", into a pack. It can also be used to re-organize
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existing packs into a single, more efficient pack.
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A pack is a collection of objects, individually compressed, with
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delta compression applied, stored in a single file, with an
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associated index file.
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Packs are used to reduce the load on mirror systems, backup
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engines, disk storage, etc.
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OPTIONS
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-------
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-a::
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Instead of incrementally packing the unpacked objects,
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pack everything referenced into a single pack.
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Especially useful when packing a repository that is used
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for private development. Use
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with `-d`. This will clean up the objects that `git prune`
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leaves behind, but `git fsck --full --dangling` shows as
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dangling.
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+
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Note that users fetching over dumb protocols will have to fetch the
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whole new pack in order to get any contained object, no matter how many
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other objects in that pack they already have locally.
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+
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Promisor packfiles are repacked separately: if there are packfiles that
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have an associated ".promisor" file, these packfiles will be repacked
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into another separate pack, and an empty ".promisor" file corresponding
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to the new separate pack will be written.
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-A::
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Same as `-a`, unless `-d` is used. Then any unreachable
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objects in a previous pack become loose, unpacked objects,
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instead of being left in the old pack. Unreachable objects
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are never intentionally added to a pack, even when repacking.
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This option prevents unreachable objects from being immediately
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deleted by way of being left in the old pack and then
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removed. Instead, the loose unreachable objects
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will be pruned according to normal expiry rules
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with the next 'git gc' invocation. See linkgit:git-gc[1].
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-d::
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After packing, if the newly created packs make some
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existing packs redundant, remove the redundant packs.
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Also run 'git prune-packed' to remove redundant
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loose object files.
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-l::
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Pass the `--local` option to 'git pack-objects'. See
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linkgit:git-pack-objects[1].
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-f::
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Pass the `--no-reuse-delta` option to `git-pack-objects`, see
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linkgit:git-pack-objects[1].
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-F::
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Pass the `--no-reuse-object` option to `git-pack-objects`, see
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linkgit:git-pack-objects[1].
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-q::
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Pass the `-q` option to 'git pack-objects'. See
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linkgit:git-pack-objects[1].
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-n::
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Do not update the server information with
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'git update-server-info'. This option skips
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updating local catalog files needed to publish
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this repository (or a direct copy of it)
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over HTTP or FTP. See linkgit:git-update-server-info[1].
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--window=<n>::
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--depth=<n>::
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These two options affect how the objects contained in the pack are
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stored using delta compression. The objects are first internally
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sorted by type, size and optionally names and compared against the
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other objects within `--window` to see if using delta compression saves
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space. `--depth` limits the maximum delta depth; making it too deep
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affects the performance on the unpacker side, because delta data needs
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to be applied that many times to get to the necessary object.
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+
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The default value for --window is 10 and --depth is 50. The maximum
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depth is 4095.
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--threads=<n>::
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This option is passed through to `git pack-objects`.
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--window-memory=<n>::
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This option provides an additional limit on top of `--window`;
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the window size will dynamically scale down so as to not take
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up more than '<n>' bytes in memory. This is useful in
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repositories with a mix of large and small objects to not run
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out of memory with a large window, but still be able to take
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advantage of the large window for the smaller objects. The
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size can be suffixed with "k", "m", or "g".
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`--window-memory=0` makes memory usage unlimited. The default
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is taken from the `pack.windowMemory` configuration variable.
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Note that the actual memory usage will be the limit multiplied
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by the number of threads used by linkgit:git-pack-objects[1].
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--max-pack-size=<n>::
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Maximum size of each output pack file. The size can be suffixed with
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"k", "m", or "g". The minimum size allowed is limited to 1 MiB.
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If specified, multiple packfiles may be created, which also
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prevents the creation of a bitmap index.
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The default is unlimited, unless the config variable
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`pack.packSizeLimit` is set.
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-b::
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--write-bitmap-index::
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Write a reachability bitmap index as part of the repack. This
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only makes sense when used with `-a` or `-A`, as the bitmaps
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must be able to refer to all reachable objects. This option
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overrides the setting of `repack.writeBitmaps`. This option
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has no effect if multiple packfiles are created.
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--pack-kept-objects::
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Include objects in `.keep` files when repacking. Note that we
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still do not delete `.keep` packs after `pack-objects` finishes.
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This means that we may duplicate objects, but this makes the
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option safe to use when there are concurrent pushes or fetches.
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This option is generally only useful if you are writing bitmaps
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with `-b` or `repack.writeBitmaps`, as it ensures that the
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bitmapped packfile has the necessary objects.
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--keep-pack=<pack-name>::
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Exclude the given pack from repacking. This is the equivalent
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of having `.keep` file on the pack. `<pack-name>` is the
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pack file name without leading directory (e.g. `pack-123.pack`).
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The option could be specified multiple times to keep multiple
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packs.
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--unpack-unreachable=<when>::
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When loosening unreachable objects, do not bother loosening any
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objects older than `<when>`. This can be used to optimize out
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the write of any objects that would be immediately pruned by
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a follow-up `git prune`.
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-k::
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--keep-unreachable::
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When used with `-ad`, any unreachable objects from existing
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packs will be appended to the end of the packfile instead of
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being removed. In addition, any unreachable loose objects will
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be packed (and their loose counterparts removed).
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-i::
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--delta-islands::
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Pass the `--delta-islands` option to `git-pack-objects`, see
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linkgit:git-pack-objects[1].
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-g=<factor>::
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--geometric=<factor>::
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Arrange resulting pack structure so that each successive pack
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contains at least `<factor>` times the number of objects as the
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next-largest pack.
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`git repack` ensures this by determining a "cut" of packfiles that need
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to be repacked into one in order to ensure a geometric progression. It
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picks the smallest set of packfiles such that as many of the larger
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packfiles (by count of objects contained in that pack) may be left
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intact.
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Unlike other repack modes, the set of objects to pack is determined
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uniquely by the set of packs being "rolled-up"; in other words, the
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packs determined to need to be combined in order to restore a geometric
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progression.
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When `--unpacked` is specified, loose objects are implicitly included in
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this "roll-up", without respect to their reachability. This is subject
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to change in the future. This option (implying a drastically different
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repack mode) is not guaranteed to work with all other combinations of
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option to `git repack`).
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Configuration
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-------------
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By default, the command passes `--delta-base-offset` option to
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'git pack-objects'; this typically results in slightly smaller packs,
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but the generated packs are incompatible with versions of Git older than
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version 1.4.4. If you need to share your repository with such ancient Git
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versions, either directly or via the dumb http protocol, then you
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need to set the configuration variable `repack.UseDeltaBaseOffset` to
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"false" and repack. Access from old Git versions over the native protocol
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is unaffected by this option as the conversion is performed on the fly
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as needed in that case.
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SEE ALSO
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--------
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linkgit:git-pack-objects[1]
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linkgit:git-prune-packed[1]
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GIT
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---
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Part of the linkgit:git[1] suite
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