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1244 lines
47 KiB
1244 lines
47 KiB
git-fast-import(1) |
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================== |
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|
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NAME |
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---- |
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git-fast-import - Backend for fast Git data importers |
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SYNOPSIS |
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-------- |
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frontend | 'git fast-import' [options] |
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DESCRIPTION |
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----------- |
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This program is usually not what the end user wants to run directly. |
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Most end users want to use one of the existing frontend programs, |
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which parses a specific type of foreign source and feeds the contents |
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stored there to 'git fast-import'. |
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|
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fast-import reads a mixed command/data stream from standard input and |
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writes one or more packfiles directly into the current repository. |
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When EOF is received on standard input, fast import writes out |
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updated branch and tag refs, fully updating the current repository |
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with the newly imported data. |
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The fast-import backend itself can import into an empty repository (one that |
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has already been initialized by 'git init') or incrementally |
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update an existing populated repository. Whether or not incremental |
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imports are supported from a particular foreign source depends on |
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the frontend program in use. |
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OPTIONS |
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------- |
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--date-format=<fmt>:: |
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Specify the type of dates the frontend will supply to |
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fast-import within `author`, `committer` and `tagger` commands. |
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See ``Date Formats'' below for details about which formats |
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are supported, and their syntax. |
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--force:: |
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Force updating modified existing branches, even if doing |
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so would cause commits to be lost (as the new commit does |
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not contain the old commit). |
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--max-pack-size=<n>:: |
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Maximum size of each output packfile. |
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The default is unlimited. |
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--big-file-threshold=<n>:: |
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Maximum size of a blob that fast-import will attempt to |
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create a delta for, expressed in bytes. The default is 512m |
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(512 MiB). Some importers may wish to lower this on systems |
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with constrained memory. |
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--depth=<n>:: |
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Maximum delta depth, for blob and tree deltification. |
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Default is 10. |
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--active-branches=<n>:: |
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Maximum number of branches to maintain active at once. |
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See ``Memory Utilization'' below for details. Default is 5. |
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--export-marks=<file>:: |
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Dumps the internal marks table to <file> when complete. |
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Marks are written one per line as `:markid SHA-1`. |
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Frontends can use this file to validate imports after they |
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have been completed, or to save the marks table across |
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incremental runs. As <file> is only opened and truncated |
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at checkpoint (or completion) the same path can also be |
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safely given to \--import-marks. |
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--import-marks=<file>:: |
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Before processing any input, load the marks specified in |
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<file>. The input file must exist, must be readable, and |
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must use the same format as produced by \--export-marks. |
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Multiple options may be supplied to import more than one |
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set of marks. If a mark is defined to different values, |
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the last file wins. |
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--relative-marks:: |
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After specifying --relative-marks= the paths specified |
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with --import-marks= and --export-marks= are relative |
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to an internal directory in the current repository. |
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In git-fast-import this means that the paths are relative |
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to the .git/info/fast-import directory. However, other |
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importers may use a different location. |
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--no-relative-marks:: |
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Negates a previous --relative-marks. Allows for combining |
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relative and non-relative marks by interweaving |
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--(no-)-relative-marks= with the --(import|export)-marks= |
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options. |
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--export-pack-edges=<file>:: |
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After creating a packfile, print a line of data to |
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<file> listing the filename of the packfile and the last |
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commit on each branch that was written to that packfile. |
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This information may be useful after importing projects |
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whose total object set exceeds the 4 GiB packfile limit, |
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as these commits can be used as edge points during calls |
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to 'git pack-objects'. |
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--quiet:: |
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Disable all non-fatal output, making fast-import silent when it |
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is successful. This option disables the output shown by |
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\--stats. |
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--stats:: |
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Display some basic statistics about the objects fast-import has |
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created, the packfiles they were stored into, and the |
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memory used by fast-import during this run. Showing this output |
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is currently the default, but can be disabled with \--quiet. |
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Performance |
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----------- |
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The design of fast-import allows it to import large projects in a minimum |
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amount of memory usage and processing time. Assuming the frontend |
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is able to keep up with fast-import and feed it a constant stream of data, |
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import times for projects holding 10+ years of history and containing |
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100,000+ individual commits are generally completed in just 1-2 |
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hours on quite modest (~$2,000 USD) hardware. |
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Most bottlenecks appear to be in foreign source data access (the |
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source just cannot extract revisions fast enough) or disk IO (fast-import |
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writes as fast as the disk will take the data). Imports will run |
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faster if the source data is stored on a different drive than the |
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destination Git repository (due to less IO contention). |
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Development Cost |
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---------------- |
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A typical frontend for fast-import tends to weigh in at approximately 200 |
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lines of Perl/Python/Ruby code. Most developers have been able to |
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create working importers in just a couple of hours, even though it |
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is their first exposure to fast-import, and sometimes even to Git. This is |
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an ideal situation, given that most conversion tools are throw-away |
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(use once, and never look back). |
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Parallel Operation |
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------------------ |
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Like 'git push' or 'git fetch', imports handled by fast-import are safe to |
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run alongside parallel `git repack -a -d` or `git gc` invocations, |
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or any other Git operation (including 'git prune', as loose objects |
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are never used by fast-import). |
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fast-import does not lock the branch or tag refs it is actively importing. |
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After the import, during its ref update phase, fast-import tests each |
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existing branch ref to verify the update will be a fast-forward |
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update (the commit stored in the ref is contained in the new |
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history of the commit to be written). If the update is not a |
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fast-forward update, fast-import will skip updating that ref and instead |
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prints a warning message. fast-import will always attempt to update all |
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branch refs, and does not stop on the first failure. |
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Branch updates can be forced with \--force, but it's recommended that |
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this only be used on an otherwise quiet repository. Using \--force |
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is not necessary for an initial import into an empty repository. |
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Technical Discussion |
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-------------------- |
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fast-import tracks a set of branches in memory. Any branch can be created |
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or modified at any point during the import process by sending a |
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`commit` command on the input stream. This design allows a frontend |
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program to process an unlimited number of branches simultaneously, |
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generating commits in the order they are available from the source |
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data. It also simplifies the frontend programs considerably. |
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fast-import does not use or alter the current working directory, or any |
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file within it. (It does however update the current Git repository, |
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as referenced by `GIT_DIR`.) Therefore an import frontend may use |
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the working directory for its own purposes, such as extracting file |
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revisions from the foreign source. This ignorance of the working |
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directory also allows fast-import to run very quickly, as it does not |
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need to perform any costly file update operations when switching |
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between branches. |
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Input Format |
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------------ |
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With the exception of raw file data (which Git does not interpret) |
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the fast-import input format is text (ASCII) based. This text based |
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format simplifies development and debugging of frontend programs, |
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especially when a higher level language such as Perl, Python or |
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Ruby is being used. |
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fast-import is very strict about its input. Where we say SP below we mean |
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*exactly* one space. Likewise LF means one (and only one) linefeed. |
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Supplying additional whitespace characters will cause unexpected |
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results, such as branch names or file names with leading or trailing |
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spaces in their name, or early termination of fast-import when it encounters |
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unexpected input. |
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Stream Comments |
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~~~~~~~~~~~~~~~ |
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To aid in debugging frontends fast-import ignores any line that |
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begins with `#` (ASCII pound/hash) up to and including the line |
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ending `LF`. A comment line may contain any sequence of bytes |
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that does not contain an LF and therefore may be used to include |
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any detailed debugging information that might be specific to the |
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frontend and useful when inspecting a fast-import data stream. |
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Date Formats |
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~~~~~~~~~~~~ |
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The following date formats are supported. A frontend should select |
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the format it will use for this import by passing the format name |
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in the \--date-format=<fmt> command line option. |
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`raw`:: |
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This is the Git native format and is `<time> SP <offutc>`. |
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It is also fast-import's default format, if \--date-format was |
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not specified. |
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+ |
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The time of the event is specified by `<time>` as the number of |
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seconds since the UNIX epoch (midnight, Jan 1, 1970, UTC) and is |
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written as an ASCII decimal integer. |
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+ |
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The local offset is specified by `<offutc>` as a positive or negative |
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offset from UTC. For example EST (which is 5 hours behind UTC) |
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would be expressed in `<tz>` by ``-0500'' while UTC is ``+0000''. |
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The local offset does not affect `<time>`; it is used only as an |
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advisement to help formatting routines display the timestamp. |
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+ |
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If the local offset is not available in the source material, use |
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``+0000'', or the most common local offset. For example many |
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organizations have a CVS repository which has only ever been accessed |
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by users who are located in the same location and timezone. In this |
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case a reasonable offset from UTC could be assumed. |
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+ |
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Unlike the `rfc2822` format, this format is very strict. Any |
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variation in formatting will cause fast-import to reject the value. |
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`rfc2822`:: |
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This is the standard email format as described by RFC 2822. |
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+ |
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An example value is ``Tue Feb 6 11:22:18 2007 -0500''. The Git |
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parser is accurate, but a little on the lenient side. It is the |
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same parser used by 'git am' when applying patches |
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received from email. |
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+ |
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Some malformed strings may be accepted as valid dates. In some of |
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these cases Git will still be able to obtain the correct date from |
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the malformed string. There are also some types of malformed |
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strings which Git will parse wrong, and yet consider valid. |
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Seriously malformed strings will be rejected. |
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+ |
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Unlike the `raw` format above, the timezone/UTC offset information |
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contained in an RFC 2822 date string is used to adjust the date |
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value to UTC prior to storage. Therefore it is important that |
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this information be as accurate as possible. |
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+ |
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If the source material uses RFC 2822 style dates, |
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the frontend should let fast-import handle the parsing and conversion |
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(rather than attempting to do it itself) as the Git parser has |
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been well tested in the wild. |
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+ |
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Frontends should prefer the `raw` format if the source material |
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already uses UNIX-epoch format, can be coaxed to give dates in that |
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format, or its format is easily convertible to it, as there is no |
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ambiguity in parsing. |
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`now`:: |
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Always use the current time and timezone. The literal |
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`now` must always be supplied for `<when>`. |
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+ |
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This is a toy format. The current time and timezone of this system |
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is always copied into the identity string at the time it is being |
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created by fast-import. There is no way to specify a different time or |
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timezone. |
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+ |
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This particular format is supplied as it's short to implement and |
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may be useful to a process that wants to create a new commit |
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right now, without needing to use a working directory or |
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'git update-index'. |
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+ |
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If separate `author` and `committer` commands are used in a `commit` |
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the timestamps may not match, as the system clock will be polled |
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twice (once for each command). The only way to ensure that both |
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author and committer identity information has the same timestamp |
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is to omit `author` (thus copying from `committer`) or to use a |
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date format other than `now`. |
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Commands |
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~~~~~~~~ |
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fast-import accepts several commands to update the current repository |
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and control the current import process. More detailed discussion |
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(with examples) of each command follows later. |
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`commit`:: |
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Creates a new branch or updates an existing branch by |
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creating a new commit and updating the branch to point at |
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the newly created commit. |
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`tag`:: |
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Creates an annotated tag object from an existing commit or |
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branch. Lightweight tags are not supported by this command, |
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as they are not recommended for recording meaningful points |
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in time. |
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`reset`:: |
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Reset an existing branch (or a new branch) to a specific |
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revision. This command must be used to change a branch to |
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a specific revision without making a commit on it. |
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`blob`:: |
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Convert raw file data into a blob, for future use in a |
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`commit` command. This command is optional and is not |
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needed to perform an import. |
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|
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`checkpoint`:: |
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Forces fast-import to close the current packfile, generate its |
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unique SHA-1 checksum and index, and start a new packfile. |
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This command is optional and is not needed to perform |
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an import. |
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|
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`progress`:: |
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Causes fast-import to echo the entire line to its own |
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standard output. This command is optional and is not needed |
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to perform an import. |
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`feature`:: |
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Require that fast-import supports the specified feature, or |
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abort if it does not. |
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`option`:: |
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Specify any of the options listed under OPTIONS that do not |
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change stream semantic to suit the frontend's needs. This |
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command is optional and is not needed to perform an import. |
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|
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`commit` |
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~~~~~~~~ |
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Create or update a branch with a new commit, recording one logical |
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change to the project. |
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|
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.... |
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'commit' SP <ref> LF |
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mark? |
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('author' (SP <name>)? SP LT <email> GT SP <when> LF)? |
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'committer' (SP <name>)? SP LT <email> GT SP <when> LF |
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data |
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('from' SP <committish> LF)? |
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('merge' SP <committish> LF)? |
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(filemodify | filedelete | filecopy | filerename | filedeleteall | notemodify)* |
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LF? |
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.... |
|
|
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where `<ref>` is the name of the branch to make the commit on. |
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Typically branch names are prefixed with `refs/heads/` in |
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Git, so importing the CVS branch symbol `RELENG-1_0` would use |
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`refs/heads/RELENG-1_0` for the value of `<ref>`. The value of |
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`<ref>` must be a valid refname in Git. As `LF` is not valid in |
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a Git refname, no quoting or escaping syntax is supported here. |
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|
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A `mark` command may optionally appear, requesting fast-import to save a |
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reference to the newly created commit for future use by the frontend |
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(see below for format). It is very common for frontends to mark |
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every commit they create, thereby allowing future branch creation |
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from any imported commit. |
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|
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The `data` command following `committer` must supply the commit |
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message (see below for `data` command syntax). To import an empty |
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commit message use a 0 length data. Commit messages are free-form |
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and are not interpreted by Git. Currently they must be encoded in |
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UTF-8, as fast-import does not permit other encodings to be specified. |
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|
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Zero or more `filemodify`, `filedelete`, `filecopy`, `filerename`, |
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`filedeleteall` and `notemodify` commands |
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may be included to update the contents of the branch prior to |
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creating the commit. These commands may be supplied in any order. |
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However it is recommended that a `filedeleteall` command precede |
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all `filemodify`, `filecopy`, `filerename` and `notemodify` commands in |
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the same commit, as `filedeleteall` wipes the branch clean (see below). |
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The `LF` after the command is optional (it used to be required). |
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`author` |
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^^^^^^^^ |
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An `author` command may optionally appear, if the author information |
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might differ from the committer information. If `author` is omitted |
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then fast-import will automatically use the committer's information for |
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the author portion of the commit. See below for a description of |
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the fields in `author`, as they are identical to `committer`. |
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|
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`committer` |
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^^^^^^^^^^^ |
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The `committer` command indicates who made this commit, and when |
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they made it. |
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|
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Here `<name>` is the person's display name (for example |
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``Com M Itter'') and `<email>` is the person's email address |
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(``cm@example.com''). `LT` and `GT` are the literal less-than (\x3c) |
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and greater-than (\x3e) symbols. These are required to delimit |
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the email address from the other fields in the line. Note that |
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`<name>` is free-form and may contain any sequence of bytes, except |
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`LT` and `LF`. It is typically UTF-8 encoded. |
|
|
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The time of the change is specified by `<when>` using the date format |
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that was selected by the \--date-format=<fmt> command line option. |
|
See ``Date Formats'' above for the set of supported formats, and |
|
their syntax. |
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|
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`from` |
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^^^^^^ |
|
The `from` command is used to specify the commit to initialize |
|
this branch from. This revision will be the first ancestor of the |
|
new commit. |
|
|
|
Omitting the `from` command in the first commit of a new branch |
|
will cause fast-import to create that commit with no ancestor. This |
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tends to be desired only for the initial commit of a project. |
|
If the frontend creates all files from scratch when making a new |
|
branch, a `merge` command may be used instead of `from` to start |
|
the commit with an empty tree. |
|
Omitting the `from` command on existing branches is usually desired, |
|
as the current commit on that branch is automatically assumed to |
|
be the first ancestor of the new commit. |
|
|
|
As `LF` is not valid in a Git refname or SHA-1 expression, no |
|
quoting or escaping syntax is supported within `<committish>`. |
|
|
|
Here `<committish>` is any of the following: |
|
|
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* The name of an existing branch already in fast-import's internal branch |
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table. If fast-import doesn't know the name, it's treated as a SHA-1 |
|
expression. |
|
|
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* A mark reference, `:<idnum>`, where `<idnum>` is the mark number. |
|
+ |
|
The reason fast-import uses `:` to denote a mark reference is this character |
|
is not legal in a Git branch name. The leading `:` makes it easy |
|
to distinguish between the mark 42 (`:42`) and the branch 42 (`42` |
|
or `refs/heads/42`), or an abbreviated SHA-1 which happened to |
|
consist only of base-10 digits. |
|
+ |
|
Marks must be declared (via `mark`) before they can be used. |
|
|
|
* A complete 40 byte or abbreviated commit SHA-1 in hex. |
|
|
|
* Any valid Git SHA-1 expression that resolves to a commit. See |
|
``SPECIFYING REVISIONS'' in linkgit:gitrevisions[7] for details. |
|
|
|
The special case of restarting an incremental import from the |
|
current branch value should be written as: |
|
---- |
|
from refs/heads/branch^0 |
|
---- |
|
The `{caret}0` suffix is necessary as fast-import does not permit a branch to |
|
start from itself, and the branch is created in memory before the |
|
`from` command is even read from the input. Adding `{caret}0` will force |
|
fast-import to resolve the commit through Git's revision parsing library, |
|
rather than its internal branch table, thereby loading in the |
|
existing value of the branch. |
|
|
|
`merge` |
|
^^^^^^^ |
|
Includes one additional ancestor commit. If the `from` command is |
|
omitted when creating a new branch, the first `merge` commit will be |
|
the first ancestor of the current commit, and the branch will start |
|
out with no files. An unlimited number of `merge` commands per |
|
commit are permitted by fast-import, thereby establishing an n-way merge. |
|
However Git's other tools never create commits with more than 15 |
|
additional ancestors (forming a 16-way merge). For this reason |
|
it is suggested that frontends do not use more than 15 `merge` |
|
commands per commit; 16, if starting a new, empty branch. |
|
|
|
Here `<committish>` is any of the commit specification expressions |
|
also accepted by `from` (see above). |
|
|
|
`filemodify` |
|
^^^^^^^^^^^^ |
|
Included in a `commit` command to add a new file or change the |
|
content of an existing file. This command has two different means |
|
of specifying the content of the file. |
|
|
|
External data format:: |
|
The data content for the file was already supplied by a prior |
|
`blob` command. The frontend just needs to connect it. |
|
+ |
|
.... |
|
'M' SP <mode> SP <dataref> SP <path> LF |
|
.... |
|
+ |
|
Here usually `<dataref>` must be either a mark reference (`:<idnum>`) |
|
set by a prior `blob` command, or a full 40-byte SHA-1 of an |
|
existing Git blob object. If `<mode>` is `040000`` then |
|
`<dataref>` must be the full 40-byte SHA-1 of an existing |
|
Git tree object or a mark reference set with `--import-marks`. |
|
|
|
Inline data format:: |
|
The data content for the file has not been supplied yet. |
|
The frontend wants to supply it as part of this modify |
|
command. |
|
+ |
|
.... |
|
'M' SP <mode> SP 'inline' SP <path> LF |
|
data |
|
.... |
|
+ |
|
See below for a detailed description of the `data` command. |
|
|
|
In both formats `<mode>` is the type of file entry, specified |
|
in octal. Git only supports the following modes: |
|
|
|
* `100644` or `644`: A normal (not-executable) file. The majority |
|
of files in most projects use this mode. If in doubt, this is |
|
what you want. |
|
* `100755` or `755`: A normal, but executable, file. |
|
* `120000`: A symlink, the content of the file will be the link target. |
|
* `160000`: A gitlink, SHA-1 of the object refers to a commit in |
|
another repository. Git links can only be specified by SHA or through |
|
a commit mark. They are used to implement submodules. |
|
* `040000`: A subdirectory. Subdirectories can only be specified by |
|
SHA or through a tree mark set with `--import-marks`. |
|
|
|
In both formats `<path>` is the complete path of the file to be added |
|
(if not already existing) or modified (if already existing). |
|
|
|
A `<path>` string must use UNIX-style directory separators (forward |
|
slash `/`), may contain any byte other than `LF`, and must not |
|
start with double quote (`"`). |
|
|
|
If an `LF` or double quote must be encoded into `<path>` shell-style |
|
quoting should be used, e.g. `"path/with\n and \" in it"`. |
|
|
|
The value of `<path>` must be in canonical form. That is it must not: |
|
|
|
* contain an empty directory component (e.g. `foo//bar` is invalid), |
|
* end with a directory separator (e.g. `foo/` is invalid), |
|
* start with a directory separator (e.g. `/foo` is invalid), |
|
* contain the special component `.` or `..` (e.g. `foo/./bar` and |
|
`foo/../bar` are invalid). |
|
|
|
It is recommended that `<path>` always be encoded using UTF-8. |
|
|
|
`filedelete` |
|
^^^^^^^^^^^^ |
|
Included in a `commit` command to remove a file or recursively |
|
delete an entire directory from the branch. If the file or directory |
|
removal makes its parent directory empty, the parent directory will |
|
be automatically removed too. This cascades up the tree until the |
|
first non-empty directory or the root is reached. |
|
|
|
.... |
|
'D' SP <path> LF |
|
.... |
|
|
|
here `<path>` is the complete path of the file or subdirectory to |
|
be removed from the branch. |
|
See `filemodify` above for a detailed description of `<path>`. |
|
|
|
`filecopy` |
|
^^^^^^^^^^^^ |
|
Recursively copies an existing file or subdirectory to a different |
|
location within the branch. The existing file or directory must |
|
exist. If the destination exists it will be completely replaced |
|
by the content copied from the source. |
|
|
|
.... |
|
'C' SP <path> SP <path> LF |
|
.... |
|
|
|
here the first `<path>` is the source location and the second |
|
`<path>` is the destination. See `filemodify` above for a detailed |
|
description of what `<path>` may look like. To use a source path |
|
that contains SP the path must be quoted. |
|
|
|
A `filecopy` command takes effect immediately. Once the source |
|
location has been copied to the destination any future commands |
|
applied to the source location will not impact the destination of |
|
the copy. |
|
|
|
`filerename` |
|
^^^^^^^^^^^^ |
|
Renames an existing file or subdirectory to a different location |
|
within the branch. The existing file or directory must exist. If |
|
the destination exists it will be replaced by the source directory. |
|
|
|
.... |
|
'R' SP <path> SP <path> LF |
|
.... |
|
|
|
here the first `<path>` is the source location and the second |
|
`<path>` is the destination. See `filemodify` above for a detailed |
|
description of what `<path>` may look like. To use a source path |
|
that contains SP the path must be quoted. |
|
|
|
A `filerename` command takes effect immediately. Once the source |
|
location has been renamed to the destination any future commands |
|
applied to the source location will create new files there and not |
|
impact the destination of the rename. |
|
|
|
Note that a `filerename` is the same as a `filecopy` followed by a |
|
`filedelete` of the source location. There is a slight performance |
|
advantage to using `filerename`, but the advantage is so small |
|
that it is never worth trying to convert a delete/add pair in |
|
source material into a rename for fast-import. This `filerename` |
|
command is provided just to simplify frontends that already have |
|
rename information and don't want bother with decomposing it into a |
|
`filecopy` followed by a `filedelete`. |
|
|
|
`filedeleteall` |
|
^^^^^^^^^^^^^^^ |
|
Included in a `commit` command to remove all files (and also all |
|
directories) from the branch. This command resets the internal |
|
branch structure to have no files in it, allowing the frontend |
|
to subsequently add all interesting files from scratch. |
|
|
|
.... |
|
'deleteall' LF |
|
.... |
|
|
|
This command is extremely useful if the frontend does not know |
|
(or does not care to know) what files are currently on the branch, |
|
and therefore cannot generate the proper `filedelete` commands to |
|
update the content. |
|
|
|
Issuing a `filedeleteall` followed by the needed `filemodify` |
|
commands to set the correct content will produce the same results |
|
as sending only the needed `filemodify` and `filedelete` commands. |
|
The `filedeleteall` approach may however require fast-import to use slightly |
|
more memory per active branch (less than 1 MiB for even most large |
|
projects); so frontends that can easily obtain only the affected |
|
paths for a commit are encouraged to do so. |
|
|
|
`notemodify` |
|
^^^^^^^^^^^^ |
|
Included in a `commit` command to add a new note (annotating a given |
|
commit) or change the content of an existing note. This command has |
|
two different means of specifying the content of the note. |
|
|
|
External data format:: |
|
The data content for the note was already supplied by a prior |
|
`blob` command. The frontend just needs to connect it to the |
|
commit that is to be annotated. |
|
+ |
|
.... |
|
'N' SP <dataref> SP <committish> LF |
|
.... |
|
+ |
|
Here `<dataref>` can be either a mark reference (`:<idnum>`) |
|
set by a prior `blob` command, or a full 40-byte SHA-1 of an |
|
existing Git blob object. |
|
|
|
Inline data format:: |
|
The data content for the note has not been supplied yet. |
|
The frontend wants to supply it as part of this modify |
|
command. |
|
+ |
|
.... |
|
'N' SP 'inline' SP <committish> LF |
|
data |
|
.... |
|
+ |
|
See below for a detailed description of the `data` command. |
|
|
|
In both formats `<committish>` is any of the commit specification |
|
expressions also accepted by `from` (see above). |
|
|
|
`mark` |
|
~~~~~~ |
|
Arranges for fast-import to save a reference to the current object, allowing |
|
the frontend to recall this object at a future point in time, without |
|
knowing its SHA-1. Here the current object is the object creation |
|
command the `mark` command appears within. This can be `commit`, |
|
`tag`, and `blob`, but `commit` is the most common usage. |
|
|
|
.... |
|
'mark' SP ':' <idnum> LF |
|
.... |
|
|
|
where `<idnum>` is the number assigned by the frontend to this mark. |
|
The value of `<idnum>` is expressed as an ASCII decimal integer. |
|
The value 0 is reserved and cannot be used as |
|
a mark. Only values greater than or equal to 1 may be used as marks. |
|
|
|
New marks are created automatically. Existing marks can be moved |
|
to another object simply by reusing the same `<idnum>` in another |
|
`mark` command. |
|
|
|
`tag` |
|
~~~~~ |
|
Creates an annotated tag referring to a specific commit. To create |
|
lightweight (non-annotated) tags see the `reset` command below. |
|
|
|
.... |
|
'tag' SP <name> LF |
|
'from' SP <committish> LF |
|
'tagger' (SP <name>)? SP LT <email> GT SP <when> LF |
|
data |
|
.... |
|
|
|
where `<name>` is the name of the tag to create. |
|
|
|
Tag names are automatically prefixed with `refs/tags/` when stored |
|
in Git, so importing the CVS branch symbol `RELENG-1_0-FINAL` would |
|
use just `RELENG-1_0-FINAL` for `<name>`, and fast-import will write the |
|
corresponding ref as `refs/tags/RELENG-1_0-FINAL`. |
|
|
|
The value of `<name>` must be a valid refname in Git and therefore |
|
may contain forward slashes. As `LF` is not valid in a Git refname, |
|
no quoting or escaping syntax is supported here. |
|
|
|
The `from` command is the same as in the `commit` command; see |
|
above for details. |
|
|
|
The `tagger` command uses the same format as `committer` within |
|
`commit`; again see above for details. |
|
|
|
The `data` command following `tagger` must supply the annotated tag |
|
message (see below for `data` command syntax). To import an empty |
|
tag message use a 0 length data. Tag messages are free-form and are |
|
not interpreted by Git. Currently they must be encoded in UTF-8, |
|
as fast-import does not permit other encodings to be specified. |
|
|
|
Signing annotated tags during import from within fast-import is not |
|
supported. Trying to include your own PGP/GPG signature is not |
|
recommended, as the frontend does not (easily) have access to the |
|
complete set of bytes which normally goes into such a signature. |
|
If signing is required, create lightweight tags from within fast-import with |
|
`reset`, then create the annotated versions of those tags offline |
|
with the standard 'git tag' process. |
|
|
|
`reset` |
|
~~~~~~~ |
|
Creates (or recreates) the named branch, optionally starting from |
|
a specific revision. The reset command allows a frontend to issue |
|
a new `from` command for an existing branch, or to create a new |
|
branch from an existing commit without creating a new commit. |
|
|
|
.... |
|
'reset' SP <ref> LF |
|
('from' SP <committish> LF)? |
|
LF? |
|
.... |
|
|
|
For a detailed description of `<ref>` and `<committish>` see above |
|
under `commit` and `from`. |
|
|
|
The `LF` after the command is optional (it used to be required). |
|
|
|
The `reset` command can also be used to create lightweight |
|
(non-annotated) tags. For example: |
|
|
|
==== |
|
reset refs/tags/938 |
|
from :938 |
|
==== |
|
|
|
would create the lightweight tag `refs/tags/938` referring to |
|
whatever commit mark `:938` references. |
|
|
|
`blob` |
|
~~~~~~ |
|
Requests writing one file revision to the packfile. The revision |
|
is not connected to any commit; this connection must be formed in |
|
a subsequent `commit` command by referencing the blob through an |
|
assigned mark. |
|
|
|
.... |
|
'blob' LF |
|
mark? |
|
data |
|
.... |
|
|
|
The mark command is optional here as some frontends have chosen |
|
to generate the Git SHA-1 for the blob on their own, and feed that |
|
directly to `commit`. This is typically more work than it's worth |
|
however, as marks are inexpensive to store and easy to use. |
|
|
|
`data` |
|
~~~~~~ |
|
Supplies raw data (for use as blob/file content, commit messages, or |
|
annotated tag messages) to fast-import. Data can be supplied using an exact |
|
byte count or delimited with a terminating line. Real frontends |
|
intended for production-quality conversions should always use the |
|
exact byte count format, as it is more robust and performs better. |
|
The delimited format is intended primarily for testing fast-import. |
|
|
|
Comment lines appearing within the `<raw>` part of `data` commands |
|
are always taken to be part of the body of the data and are therefore |
|
never ignored by fast-import. This makes it safe to import any |
|
file/message content whose lines might start with `#`. |
|
|
|
Exact byte count format:: |
|
The frontend must specify the number of bytes of data. |
|
+ |
|
.... |
|
'data' SP <count> LF |
|
<raw> LF? |
|
.... |
|
+ |
|
where `<count>` is the exact number of bytes appearing within |
|
`<raw>`. The value of `<count>` is expressed as an ASCII decimal |
|
integer. The `LF` on either side of `<raw>` is not |
|
included in `<count>` and will not be included in the imported data. |
|
+ |
|
The `LF` after `<raw>` is optional (it used to be required) but |
|
recommended. Always including it makes debugging a fast-import |
|
stream easier as the next command always starts in column 0 |
|
of the next line, even if `<raw>` did not end with an `LF`. |
|
|
|
Delimited format:: |
|
A delimiter string is used to mark the end of the data. |
|
fast-import will compute the length by searching for the delimiter. |
|
This format is primarily useful for testing and is not |
|
recommended for real data. |
|
+ |
|
.... |
|
'data' SP '<<' <delim> LF |
|
<raw> LF |
|
<delim> LF |
|
LF? |
|
.... |
|
+ |
|
where `<delim>` is the chosen delimiter string. The string `<delim>` |
|
must not appear on a line by itself within `<raw>`, as otherwise |
|
fast-import will think the data ends earlier than it really does. The `LF` |
|
immediately trailing `<raw>` is part of `<raw>`. This is one of |
|
the limitations of the delimited format, it is impossible to supply |
|
a data chunk which does not have an LF as its last byte. |
|
+ |
|
The `LF` after `<delim> LF` is optional (it used to be required). |
|
|
|
`checkpoint` |
|
~~~~~~~~~~~~ |
|
Forces fast-import to close the current packfile, start a new one, and to |
|
save out all current branch refs, tags and marks. |
|
|
|
.... |
|
'checkpoint' LF |
|
LF? |
|
.... |
|
|
|
Note that fast-import automatically switches packfiles when the current |
|
packfile reaches \--max-pack-size, or 4 GiB, whichever limit is |
|
smaller. During an automatic packfile switch fast-import does not update |
|
the branch refs, tags or marks. |
|
|
|
As a `checkpoint` can require a significant amount of CPU time and |
|
disk IO (to compute the overall pack SHA-1 checksum, generate the |
|
corresponding index file, and update the refs) it can easily take |
|
several minutes for a single `checkpoint` command to complete. |
|
|
|
Frontends may choose to issue checkpoints during extremely large |
|
and long running imports, or when they need to allow another Git |
|
process access to a branch. However given that a 30 GiB Subversion |
|
repository can be loaded into Git through fast-import in about 3 hours, |
|
explicit checkpointing may not be necessary. |
|
|
|
The `LF` after the command is optional (it used to be required). |
|
|
|
`progress` |
|
~~~~~~~~~~ |
|
Causes fast-import to print the entire `progress` line unmodified to |
|
its standard output channel (file descriptor 1) when the command is |
|
processed from the input stream. The command otherwise has no impact |
|
on the current import, or on any of fast-import's internal state. |
|
|
|
.... |
|
'progress' SP <any> LF |
|
LF? |
|
.... |
|
|
|
The `<any>` part of the command may contain any sequence of bytes |
|
that does not contain `LF`. The `LF` after the command is optional. |
|
Callers may wish to process the output through a tool such as sed to |
|
remove the leading part of the line, for example: |
|
|
|
==== |
|
frontend | git fast-import | sed 's/^progress //' |
|
==== |
|
|
|
Placing a `progress` command immediately after a `checkpoint` will |
|
inform the reader when the `checkpoint` has been completed and it |
|
can safely access the refs that fast-import updated. |
|
|
|
`feature` |
|
~~~~~~~~~ |
|
Require that fast-import supports the specified feature, or abort if |
|
it does not. |
|
|
|
.... |
|
'feature' SP <feature> LF |
|
.... |
|
|
|
The <feature> part of the command may be any string matching |
|
^[a-zA-Z][a-zA-Z-]*$ and should be understood by fast-import. |
|
|
|
Feature work identical as their option counterparts with the |
|
exception of the import-marks feature, see below. |
|
|
|
The following features are currently supported: |
|
|
|
* date-format |
|
* import-marks |
|
* export-marks |
|
* relative-marks |
|
* no-relative-marks |
|
* force |
|
|
|
The import-marks behaves differently from when it is specified as |
|
commandline option in that only one "feature import-marks" is allowed |
|
per stream. Also, any --import-marks= specified on the commandline |
|
will override those from the stream (if any). |
|
|
|
`option` |
|
~~~~~~~~ |
|
Processes the specified option so that git fast-import behaves in a |
|
way that suits the frontend's needs. |
|
Note that options specified by the frontend are overridden by any |
|
options the user may specify to git fast-import itself. |
|
|
|
.... |
|
'option' SP <option> LF |
|
.... |
|
|
|
The `<option>` part of the command may contain any of the options |
|
listed in the OPTIONS section that do not change import semantics, |
|
without the leading '--' and is treated in the same way. |
|
|
|
Option commands must be the first commands on the input (not counting |
|
feature commands), to give an option command after any non-option |
|
command is an error. |
|
|
|
The following commandline options change import semantics and may therefore |
|
not be passed as option: |
|
|
|
* date-format |
|
* import-marks |
|
* export-marks |
|
* force |
|
|
|
Crash Reports |
|
------------- |
|
If fast-import is supplied invalid input it will terminate with a |
|
non-zero exit status and create a crash report in the top level of |
|
the Git repository it was importing into. Crash reports contain |
|
a snapshot of the internal fast-import state as well as the most |
|
recent commands that lead up to the crash. |
|
|
|
All recent commands (including stream comments, file changes and |
|
progress commands) are shown in the command history within the crash |
|
report, but raw file data and commit messages are excluded from the |
|
crash report. This exclusion saves space within the report file |
|
and reduces the amount of buffering that fast-import must perform |
|
during execution. |
|
|
|
After writing a crash report fast-import will close the current |
|
packfile and export the marks table. This allows the frontend |
|
developer to inspect the repository state and resume the import from |
|
the point where it crashed. The modified branches and tags are not |
|
updated during a crash, as the import did not complete successfully. |
|
Branch and tag information can be found in the crash report and |
|
must be applied manually if the update is needed. |
|
|
|
An example crash: |
|
|
|
==== |
|
$ cat >in <<END_OF_INPUT |
|
# my very first test commit |
|
commit refs/heads/master |
|
committer Shawn O. Pearce <spearce> 19283 -0400 |
|
# who is that guy anyway? |
|
data <<EOF |
|
this is my commit |
|
EOF |
|
M 644 inline .gitignore |
|
data <<EOF |
|
.gitignore |
|
EOF |
|
M 777 inline bob |
|
END_OF_INPUT |
|
|
|
$ git fast-import <in |
|
fatal: Corrupt mode: M 777 inline bob |
|
fast-import: dumping crash report to .git/fast_import_crash_8434 |
|
|
|
$ cat .git/fast_import_crash_8434 |
|
fast-import crash report: |
|
fast-import process: 8434 |
|
parent process : 1391 |
|
at Sat Sep 1 00:58:12 2007 |
|
|
|
fatal: Corrupt mode: M 777 inline bob |
|
|
|
Most Recent Commands Before Crash |
|
--------------------------------- |
|
# my very first test commit |
|
commit refs/heads/master |
|
committer Shawn O. Pearce <spearce> 19283 -0400 |
|
# who is that guy anyway? |
|
data <<EOF |
|
M 644 inline .gitignore |
|
data <<EOF |
|
* M 777 inline bob |
|
|
|
Active Branch LRU |
|
----------------- |
|
active_branches = 1 cur, 5 max |
|
|
|
pos clock name |
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
1) 0 refs/heads/master |
|
|
|
Inactive Branches |
|
----------------- |
|
refs/heads/master: |
|
status : active loaded dirty |
|
tip commit : 0000000000000000000000000000000000000000 |
|
old tree : 0000000000000000000000000000000000000000 |
|
cur tree : 0000000000000000000000000000000000000000 |
|
commit clock: 0 |
|
last pack : |
|
|
|
|
|
------------------- |
|
END OF CRASH REPORT |
|
==== |
|
|
|
Tips and Tricks |
|
--------------- |
|
The following tips and tricks have been collected from various |
|
users of fast-import, and are offered here as suggestions. |
|
|
|
Use One Mark Per Commit |
|
~~~~~~~~~~~~~~~~~~~~~~~ |
|
When doing a repository conversion, use a unique mark per commit |
|
(`mark :<n>`) and supply the \--export-marks option on the command |
|
line. fast-import will dump a file which lists every mark and the Git |
|
object SHA-1 that corresponds to it. If the frontend can tie |
|
the marks back to the source repository, it is easy to verify the |
|
accuracy and completeness of the import by comparing each Git |
|
commit to the corresponding source revision. |
|
|
|
Coming from a system such as Perforce or Subversion this should be |
|
quite simple, as the fast-import mark can also be the Perforce changeset |
|
number or the Subversion revision number. |
|
|
|
Freely Skip Around Branches |
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
Don't bother trying to optimize the frontend to stick to one branch |
|
at a time during an import. Although doing so might be slightly |
|
faster for fast-import, it tends to increase the complexity of the frontend |
|
code considerably. |
|
|
|
The branch LRU builtin to fast-import tends to behave very well, and the |
|
cost of activating an inactive branch is so low that bouncing around |
|
between branches has virtually no impact on import performance. |
|
|
|
Handling Renames |
|
~~~~~~~~~~~~~~~~ |
|
When importing a renamed file or directory, simply delete the old |
|
name(s) and modify the new name(s) during the corresponding commit. |
|
Git performs rename detection after-the-fact, rather than explicitly |
|
during a commit. |
|
|
|
Use Tag Fixup Branches |
|
~~~~~~~~~~~~~~~~~~~~~~ |
|
Some other SCM systems let the user create a tag from multiple |
|
files which are not from the same commit/changeset. Or to create |
|
tags which are a subset of the files available in the repository. |
|
|
|
Importing these tags as-is in Git is impossible without making at |
|
least one commit which ``fixes up'' the files to match the content |
|
of the tag. Use fast-import's `reset` command to reset a dummy branch |
|
outside of your normal branch space to the base commit for the tag, |
|
then commit one or more file fixup commits, and finally tag the |
|
dummy branch. |
|
|
|
For example since all normal branches are stored under `refs/heads/` |
|
name the tag fixup branch `TAG_FIXUP`. This way it is impossible for |
|
the fixup branch used by the importer to have namespace conflicts |
|
with real branches imported from the source (the name `TAG_FIXUP` |
|
is not `refs/heads/TAG_FIXUP`). |
|
|
|
When committing fixups, consider using `merge` to connect the |
|
commit(s) which are supplying file revisions to the fixup branch. |
|
Doing so will allow tools such as 'git blame' to track |
|
through the real commit history and properly annotate the source |
|
files. |
|
|
|
After fast-import terminates the frontend will need to do `rm .git/TAG_FIXUP` |
|
to remove the dummy branch. |
|
|
|
Import Now, Repack Later |
|
~~~~~~~~~~~~~~~~~~~~~~~~ |
|
As soon as fast-import completes the Git repository is completely valid |
|
and ready for use. Typically this takes only a very short time, |
|
even for considerably large projects (100,000+ commits). |
|
|
|
However repacking the repository is necessary to improve data |
|
locality and access performance. It can also take hours on extremely |
|
large projects (especially if -f and a large \--window parameter is |
|
used). Since repacking is safe to run alongside readers and writers, |
|
run the repack in the background and let it finish when it finishes. |
|
There is no reason to wait to explore your new Git project! |
|
|
|
If you choose to wait for the repack, don't try to run benchmarks |
|
or performance tests until repacking is completed. fast-import outputs |
|
suboptimal packfiles that are simply never seen in real use |
|
situations. |
|
|
|
Repacking Historical Data |
|
~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
If you are repacking very old imported data (e.g. older than the |
|
last year), consider expending some extra CPU time and supplying |
|
\--window=50 (or higher) when you run 'git repack'. |
|
This will take longer, but will also produce a smaller packfile. |
|
You only need to expend the effort once, and everyone using your |
|
project will benefit from the smaller repository. |
|
|
|
Include Some Progress Messages |
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
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Every once in a while have your frontend emit a `progress` message |
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to fast-import. The contents of the messages are entirely free-form, |
|
so one suggestion would be to output the current month and year |
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each time the current commit date moves into the next month. |
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Your users will feel better knowing how much of the data stream |
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has been processed. |
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Packfile Optimization |
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--------------------- |
|
When packing a blob fast-import always attempts to deltify against the last |
|
blob written. Unless specifically arranged for by the frontend, |
|
this will probably not be a prior version of the same file, so the |
|
generated delta will not be the smallest possible. The resulting |
|
packfile will be compressed, but will not be optimal. |
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|
|
Frontends which have efficient access to all revisions of a |
|
single file (for example reading an RCS/CVS ,v file) can choose |
|
to supply all revisions of that file as a sequence of consecutive |
|
`blob` commands. This allows fast-import to deltify the different file |
|
revisions against each other, saving space in the final packfile. |
|
Marks can be used to later identify individual file revisions during |
|
a sequence of `commit` commands. |
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|
|
The packfile(s) created by fast-import do not encourage good disk access |
|
patterns. This is caused by fast-import writing the data in the order |
|
it is received on standard input, while Git typically organizes |
|
data within packfiles to make the most recent (current tip) data |
|
appear before historical data. Git also clusters commits together, |
|
speeding up revision traversal through better cache locality. |
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|
|
For this reason it is strongly recommended that users repack the |
|
repository with `git repack -a -d` after fast-import completes, allowing |
|
Git to reorganize the packfiles for faster data access. If blob |
|
deltas are suboptimal (see above) then also adding the `-f` option |
|
to force recomputation of all deltas can significantly reduce the |
|
final packfile size (30-50% smaller can be quite typical). |
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Memory Utilization |
|
------------------ |
|
There are a number of factors which affect how much memory fast-import |
|
requires to perform an import. Like critical sections of core |
|
Git, fast-import uses its own memory allocators to amortize any overheads |
|
associated with malloc. In practice fast-import tends to amortize any |
|
malloc overheads to 0, due to its use of large block allocations. |
|
|
|
per object |
|
~~~~~~~~~~ |
|
fast-import maintains an in-memory structure for every object written in |
|
this execution. On a 32 bit system the structure is 32 bytes, |
|
on a 64 bit system the structure is 40 bytes (due to the larger |
|
pointer sizes). Objects in the table are not deallocated until |
|
fast-import terminates. Importing 2 million objects on a 32 bit system |
|
will require approximately 64 MiB of memory. |
|
|
|
The object table is actually a hashtable keyed on the object name |
|
(the unique SHA-1). This storage configuration allows fast-import to reuse |
|
an existing or already written object and avoid writing duplicates |
|
to the output packfile. Duplicate blobs are surprisingly common |
|
in an import, typically due to branch merges in the source. |
|
|
|
per mark |
|
~~~~~~~~ |
|
Marks are stored in a sparse array, using 1 pointer (4 bytes or 8 |
|
bytes, depending on pointer size) per mark. Although the array |
|
is sparse, frontends are still strongly encouraged to use marks |
|
between 1 and n, where n is the total number of marks required for |
|
this import. |
|
|
|
per branch |
|
~~~~~~~~~~ |
|
Branches are classified as active and inactive. The memory usage |
|
of the two classes is significantly different. |
|
|
|
Inactive branches are stored in a structure which uses 96 or 120 |
|
bytes (32 bit or 64 bit systems, respectively), plus the length of |
|
the branch name (typically under 200 bytes), per branch. fast-import will |
|
easily handle as many as 10,000 inactive branches in under 2 MiB |
|
of memory. |
|
|
|
Active branches have the same overhead as inactive branches, but |
|
also contain copies of every tree that has been recently modified on |
|
that branch. If subtree `include` has not been modified since the |
|
branch became active, its contents will not be loaded into memory, |
|
but if subtree `src` has been modified by a commit since the branch |
|
became active, then its contents will be loaded in memory. |
|
|
|
As active branches store metadata about the files contained on that |
|
branch, their in-memory storage size can grow to a considerable size |
|
(see below). |
|
|
|
fast-import automatically moves active branches to inactive status based on |
|
a simple least-recently-used algorithm. The LRU chain is updated on |
|
each `commit` command. The maximum number of active branches can be |
|
increased or decreased on the command line with \--active-branches=. |
|
|
|
per active tree |
|
~~~~~~~~~~~~~~~ |
|
Trees (aka directories) use just 12 bytes of memory on top of the |
|
memory required for their entries (see ``per active file'' below). |
|
The cost of a tree is virtually 0, as its overhead amortizes out |
|
over the individual file entries. |
|
|
|
per active file entry |
|
~~~~~~~~~~~~~~~~~~~~~ |
|
Files (and pointers to subtrees) within active trees require 52 or 64 |
|
bytes (32/64 bit platforms) per entry. To conserve space, file and |
|
tree names are pooled in a common string table, allowing the filename |
|
``Makefile'' to use just 16 bytes (after including the string header |
|
overhead) no matter how many times it occurs within the project. |
|
|
|
The active branch LRU, when coupled with the filename string pool |
|
and lazy loading of subtrees, allows fast-import to efficiently import |
|
projects with 2,000+ branches and 45,114+ files in a very limited |
|
memory footprint (less than 2.7 MiB per active branch). |
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|
|
|
Author |
|
------ |
|
Written by Shawn O. Pearce <spearce@spearce.org>. |
|
|
|
Documentation |
|
-------------- |
|
Documentation by Shawn O. Pearce <spearce@spearce.org>. |
|
|
|
GIT |
|
--- |
|
Part of the linkgit:git[1] suite
|
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|