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When pruning objects with `--cruft`, `git repack` offers some
flexibility when selecting the set of which objects are pruned via the
`--cruft-expiration` option.
This is useful for expiring objects which are older than the grace
period, making races where to-be-pruned objects become reachable and
then ancestors of freshly pushed objects, leaving the repository in a
corrupt state after pruning substantially less likely [1].
But in practice, such races are impossible to avoid entirely, no matter
how long the grace period is. To prevent this race, it is often
advisable to temporarily put a repository into a read-only state. But in
practice, this is not always practical, and so some middle ground would
be nice.
This patch introduces a new option, `--expire-to`, which teaches `git
repack` to write an additional cruft pack containing just the objects
which were pruned from the repository. The caller can specify a
directory outside of the current repository as the destination for this
second cruft pack.
This makes it possible to prune objects from a repository, while still
holding onto a supplemental copy of them outside of the original
repository. Having this copy on-disk makes it substantially easier to
recover objects when the aforementioned race is encountered.
`--expire-to` is implemented in a somewhat convoluted manner, which is
to take advantage of the fact that the first time `write_cruft_pack()`
is called, it adds the name of the cruft pack to the `names` string
list. That means the second time we call `write_cruft_pack()`, objects
in the previously-written cruft pack will be excluded.
As long as the caller ensures that no objects are expired during the
second pass, this is sufficient to generate a cruft pack containing all
objects which don't appear in any of the new packs written by `git
repack`, including the cruft pack. In other words, all of the objects
which are about to be pruned from the repository.
It is important to note that the destination in `--expire-to` does not
necessarily need to be a Git repository (though it can be) Notably, the
expired packs do not contain all ancestors of expired objects. So if the
source repository contains something like:
<unreachable>
/
C1 --- C2
\
refs/heads/master
where C2 is unreachable, but has a parent (C1) which is reachable, and
C2 would be pruned, then the expiry pack will contain only C2, not C1.
[1]: https://lore.kernel.org/git/20190319001829.GL29661@sigill.intra.peff.net/
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
248 lines
9.3 KiB
Text
248 lines
9.3 KiB
Text
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] [-m] [--window=<n>] [--depth=<n>] [--threads=<n>] [--keep-pack=<pack-name>] [--write-midx]
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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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--cruft::
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Same as `-a`, unless `-d` is used. Then any unreachable objects
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are packed into a separate cruft pack. Unreachable objects can
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be pruned using the normal expiry rules with the next `git gc`
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invocation (see linkgit:git-gc[1]). Incompatible with `-k`.
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--cruft-expiration=<approxidate>::
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Expire unreachable objects older than `<approxidate>`
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immediately instead of waiting for the next `git gc` invocation.
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Only useful with `--cruft -d`.
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--expire-to=<dir>::
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Write a cruft pack containing pruned objects (if any) to the
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directory `<dir>`. This option is useful for keeping a copy of
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any pruned objects in a separate directory as a backup. Only
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useful with `--cruft -d`.
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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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--quiet::
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Show no progress over the standard error stream and pass the `-q`
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option to 'git pack-objects'. See 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. Note that this option may result in
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a larger and slower repository; see the discussion in
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`pack.packSizeLimit`.
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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`, `-A` or `-m`, 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, unless writing a
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MIDX (in which case a multi-pack bitmap is 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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When writing a multi-pack bitmap, `git repack` selects the largest resulting
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pack as the preferred pack for object selection by the MIDX (see
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linkgit:git-multi-pack-index[1]).
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-m::
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--write-midx::
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Write a multi-pack index (see linkgit:git-multi-pack-index[1])
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containing the non-redundant packs.
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CONFIGURATION
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-------------
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Various configuration variables affect packing, see
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linkgit:git-config[1] (search for "pack" and "delta").
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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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Delta compression is not used on objects larger than the
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`core.bigFileThreshold` configuration variable and on files with the
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attribute `delta` set to false.
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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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