75b97fec17
Introduce new repository extension option:
`extensions.partialclone`
See the update to Documentation/technical/repository-version.txt
in this patch for more information.
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
101 lines
4.0 KiB
Plaintext
101 lines
4.0 KiB
Plaintext
Git Repository Format Versions
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==============================
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Every git repository is marked with a numeric version in the
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`core.repositoryformatversion` key of its `config` file. This version
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specifies the rules for operating on the on-disk repository data. An
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implementation of git which does not understand a particular version
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advertised by an on-disk repository MUST NOT operate on that repository;
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doing so risks not only producing wrong results, but actually losing
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data.
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Because of this rule, version bumps should be kept to an absolute
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minimum. Instead, we generally prefer these strategies:
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- bumping format version numbers of individual data files (e.g.,
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index, packfiles, etc). This restricts the incompatibilities only to
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those files.
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- introducing new data that gracefully degrades when used by older
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clients (e.g., pack bitmap files are ignored by older clients, which
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simply do not take advantage of the optimization they provide).
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A whole-repository format version bump should only be part of a change
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that cannot be independently versioned. For instance, if one were to
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change the reachability rules for objects, or the rules for locking
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refs, that would require a bump of the repository format version.
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Note that this applies only to accessing the repository's disk contents
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directly. An older client which understands only format `0` may still
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connect via `git://` to a repository using format `1`, as long as the
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server process understands format `1`.
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The preferred strategy for rolling out a version bump (whether whole
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repository or for a single file) is to teach git to read the new format,
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and allow writing the new format with a config switch or command line
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option (for experimentation or for those who do not care about backwards
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compatibility with older gits). Then after a long period to allow the
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reading capability to become common, we may switch to writing the new
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format by default.
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The currently defined format versions are:
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Version `0`
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-----------
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This is the format defined by the initial version of git, including but
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not limited to the format of the repository directory, the repository
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configuration file, and the object and ref storage. Specifying the
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complete behavior of git is beyond the scope of this document.
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Version `1`
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-----------
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This format is identical to version `0`, with the following exceptions:
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1. When reading the `core.repositoryformatversion` variable, a git
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implementation which supports version 1 MUST also read any
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configuration keys found in the `extensions` section of the
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configuration file.
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2. If a version-1 repository specifies any `extensions.*` keys that
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the running git has not implemented, the operation MUST NOT
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proceed. Similarly, if the value of any known key is not understood
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by the implementation, the operation MUST NOT proceed.
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Note that if no extensions are specified in the config file, then
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`core.repositoryformatversion` SHOULD be set to `0` (setting it to `1`
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provides no benefit, and makes the repository incompatible with older
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implementations of git).
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This document will serve as the master list for extensions. Any
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implementation wishing to define a new extension should make a note of
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it here, in order to claim the name.
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The defined extensions are:
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`noop`
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~~~~~~
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This extension does not change git's behavior at all. It is useful only
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for testing format-1 compatibility.
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`preciousObjects`
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~~~~~~~~~~~~~~~~~
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When the config key `extensions.preciousObjects` is set to `true`,
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objects in the repository MUST NOT be deleted (e.g., by `git-prune` or
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`git repack -d`).
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`partialclone`
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~~~~~~~~~~~~~~
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When the config key `extensions.partialclone` is set, it indicates
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that the repo was created with a partial clone (or later performed
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a partial fetch) and that the remote may have omitted sending
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certain unwanted objects. Such a remote is called a "promisor remote"
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and it promises that all such omitted objects can be fetched from it
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in the future.
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The value of this key is the name of the promisor remote.
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