08944d1c22
To figure out which commits we can write a bitmap for, the multi-pack index/bitmap code does a reachability traversal, marking any commit which can be found in the MIDX as eligible to receive a bitmap. This approach will cause a problem when multi-pack bitmaps are able to be generated from `git repack`, since the reference tips can change during the repack. Even though we ignore commits that don't exist in the MIDX (when doing a scan of the ref tips), it's possible that a commit in the MIDX reaches something that isn't. This can happen when a multi-pack index contains some pack which refers to loose objects (e.g., if a pack was pushed after starting the repack but before generating the MIDX which depends on an object which is stored as loose in the repository, and by definition isn't included in the multi-pack index). By taking a snapshot of the references before we start repacking, we can close that race window. In the above scenario (where we have a packed object pointing at a loose one), we'll either (a) take a snapshot of the references before seeing the packed one, or (b) take it after, at which point we can guarantee that the loose object will be packed and included in the MIDX. This patch does just that. It writes a temporary "reference snapshot", which is a list of OIDs that are at the ref tips before writing a multi-pack bitmap. References that are "preferred" (i.e,. are a suffix of at least one value of the 'pack.preferBitmapTips' configuration) are marked with a special '+'. The format is simple: one line per commit at each tip, with an optional '+' at the beginning (for preferred references, as described above). When provided, the reference snapshot is used to drive bitmap selection instead of the MIDX code doing its own traversal. When it isn't provided, the usual traversal takes place instead. Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
138 lines
4.4 KiB
Plaintext
138 lines
4.4 KiB
Plaintext
git-multi-pack-index(1)
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=======================
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NAME
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----
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git-multi-pack-index - Write and verify multi-pack-indexes
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SYNOPSIS
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--------
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[verse]
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'git multi-pack-index' [--object-dir=<dir>] [--[no-]progress]
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[--preferred-pack=<pack>] [--[no-]bitmap] <subcommand>
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DESCRIPTION
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-----------
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Write or verify a multi-pack-index (MIDX) file.
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OPTIONS
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-------
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--object-dir=<dir>::
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Use given directory for the location of Git objects. We check
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`<dir>/packs/multi-pack-index` for the current MIDX file, and
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`<dir>/packs` for the pack-files to index.
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+
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`<dir>` must be an alternate of the current repository.
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--[no-]progress::
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Turn progress on/off explicitly. If neither is specified, progress is
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shown if standard error is connected to a terminal.
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The following subcommands are available:
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write::
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Write a new MIDX file. The following options are available for
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the `write` sub-command:
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+
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--
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--preferred-pack=<pack>::
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Optionally specify the tie-breaking pack used when
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multiple packs contain the same object. `<pack>` must
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contain at least one object. If not given, ties are
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broken in favor of the pack with the lowest mtime.
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--[no-]bitmap::
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Control whether or not a multi-pack bitmap is written.
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--stdin-packs::
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Write a multi-pack index containing only the set of
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line-delimited pack index basenames provided over stdin.
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--refs-snapshot=<path>::
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With `--bitmap`, optionally specify a file which
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contains a "refs snapshot" taken prior to repacking.
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+
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A reference snapshot is composed of line-delimited OIDs corresponding to
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the reference tips, usually taken by `git repack` prior to generating a
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new pack. A line may optionally start with a `+` character to indicate
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that the reference which corresponds to that OID is "preferred" (see
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linkgit:git-config[1]'s `pack.preferBitmapTips`.)
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+
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The file given at `<path>` is expected to be readable, and can contain
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duplicates. (If a given OID is given more than once, it is marked as
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preferred if at least one instance of it begins with the special `+`
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marker).
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--
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verify::
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Verify the contents of the MIDX file.
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expire::
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Delete the pack-files that are tracked by the MIDX file, but
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have no objects referenced by the MIDX. Rewrite the MIDX file
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afterward to remove all references to these pack-files.
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repack::
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Create a new pack-file containing objects in small pack-files
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referenced by the multi-pack-index. If the size given by the
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`--batch-size=<size>` argument is zero, then create a pack
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containing all objects referenced by the multi-pack-index. For
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a non-zero batch size, Select the pack-files by examining packs
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from oldest-to-newest, computing the "expected size" by counting
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the number of objects in the pack referenced by the
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multi-pack-index, then divide by the total number of objects in
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the pack and multiply by the pack size. We select packs with
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expected size below the batch size until the set of packs have
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total expected size at least the batch size, or all pack-files
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are considered. If only one pack-file is selected, then do
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nothing. If a new pack-file is created, rewrite the
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multi-pack-index to reference the new pack-file. A later run of
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'git multi-pack-index expire' will delete the pack-files that
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were part of this batch.
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+
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If `repack.packKeptObjects` is `false`, then any pack-files with an
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associated `.keep` file will not be selected for the batch to repack.
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EXAMPLES
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--------
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* Write a MIDX file for the packfiles in the current .git folder.
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+
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-----------------------------------------------
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$ git multi-pack-index write
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-----------------------------------------------
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* Write a MIDX file for the packfiles in the current .git folder with a
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corresponding bitmap.
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+
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-------------------------------------------------------------
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$ git multi-pack-index write --preferred-pack=<pack> --bitmap
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-------------------------------------------------------------
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* Write a MIDX file for the packfiles in an alternate object store.
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+
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-----------------------------------------------
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$ git multi-pack-index --object-dir <alt> write
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-----------------------------------------------
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* Verify the MIDX file for the packfiles in the current .git folder.
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+
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-----------------------------------------------
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$ git multi-pack-index verify
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-----------------------------------------------
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SEE ALSO
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--------
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See link:technical/multi-pack-index.html[The Multi-Pack-Index Design
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Document] and link:technical/pack-format.html[The Multi-Pack-Index
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Format] for more information on the multi-pack-index feature.
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GIT
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---
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Part of the linkgit:git[1] suite
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