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GIT-FAST-IMPORT(1)                          Git Manual                         GIT-FAST-IMPORT(1)

NAME
       git-fast-import - Backend for fast Git data importers

SYNOPSIS
       frontend | git fast-import [options]

DESCRIPTION
       This program is usually not what the end user wants to run directly. Most end users want
       to use one of the existing frontend programs, which parses a specific type of foreign
       source and feeds the contents stored there to git fast-import.

       fast-import reads a mixed command/data stream from standard input and writes one or more
       packfiles directly into the current repository. When EOF is received on standard input,
       fast import writes out updated branch and tag refs, fully updating the current repository
       with the newly imported data.

       The fast-import backend itself can import into an empty repository (one that has already
       been initialized by git init) or incrementally update an existing populated repository.
       Whether or not incremental imports are supported from a particular foreign source depends
       on the frontend program in use.

OPTIONS
       --force
           Force updating modified existing branches, even if doing so would cause commits to be
           lost (as the new commit does not contain the old commit).

       --quiet
           Disable all non-fatal output, making fast-import silent when it is successful. This
           option disables the output shown by --stats.

       --stats
           Display some basic statistics about the objects fast-import has created, the packfiles
           they were stored into, and the memory used by fast-import during this run. Showing
           this output is currently the default, but can be disabled with --quiet.

   Options for Frontends
       --cat-blob-fd=
           Write responses to get-mark, cat-blob, and ls queries to the file descriptor 
           instead of stdout. Allows progress output intended for the end-user to be separated
           from other output.

       --date-format=
           Specify the type of dates the frontend will supply to fast-import within author,
           committer and tagger commands. See “Date Formats” below for details about which
           formats are supported, and their syntax.

       --done
           Terminate with error if there is no done command at the end of the stream. This option
           might be useful for detecting errors that cause the frontend to terminate before it
           has started to write a stream.

   Locations of Marks Files
       --export-marks=
           Dumps the internal marks table to  when complete. Marks are written one per line
           as :markid SHA-1. Frontends can use this file to validate imports after they have been
           completed, or to save the marks table across incremental runs. As  is only
           opened and truncated at checkpoint (or completion) the same path can also be safely
           given to --import-marks.

       --import-marks=
           Before processing any input, load the marks specified in . The input file must
           exist, must be readable, and must use the same format as produced by --export-marks.
           Multiple options may be supplied to import more than one set of marks. If a mark is
           defined to different values, the last file wins.

       --import-marks-if-exists=
           Like --import-marks but instead of erroring out, silently skips the file if it does
           not exist.

       --[no-]relative-marks
           After specifying --relative-marks the paths specified with --import-marks= and
           --export-marks= are relative to an internal directory in the current repository. In
           git-fast-import this means that the paths are relative to the .git/info/fast-import
           directory. However, other importers may use a different location.

           Relative and non-relative marks may be combined by interweaving --(no-)-relative-marks
           with the --(import|export)-marks= options.

   Performance and Compression Tuning
       --active-branches=
           Maximum number of branches to maintain active at once. See “Memory Utilization” below
           for details. Default is 5.

       --big-file-threshold=
           Maximum size of a blob that fast-import will attempt to create a delta for, expressed
           in bytes. The default is 512m (512 MiB). Some importers may wish to lower this on
           systems with constrained memory.

       --depth=
           Maximum delta depth, for blob and tree deltification. Default is 10.

       --export-pack-edges=
           After creating a packfile, print a line of data to  listing the filename of the
           packfile and the last commit on each branch that was written to that packfile. This
           information may be useful after importing projects whose total object set exceeds the
           4 GiB packfile limit, as these commits can be used as edge points during calls to git
           pack-objects.

       --max-pack-size=
           Maximum size of each output packfile. The default is unlimited.

PERFORMANCE
       The design of fast-import allows it to import large projects in a minimum amount of memory
       usage and processing time. Assuming the frontend is able to keep up with fast-import and
       feed it a constant stream of data, import times for projects holding 10+ years of history
       and containing 100,000+ individual commits are generally completed in just 1-2 hours on
       quite modest (~$2,000 USD) hardware.

       Most bottlenecks appear to be in foreign source data access (the source just cannot
       extract revisions fast enough) or disk IO (fast-import writes as fast as the disk will
       take the data). Imports will run faster if the source data is stored on a different drive
       than the destination Git repository (due to less IO contention).

DEVELOPMENT COST
       A typical frontend for fast-import tends to weigh in at approximately 200 lines of
       Perl/Python/Ruby code. Most developers have been able to create working importers in just
       a couple of hours, even though it is their first exposure to fast-import, and sometimes
       even to Git. This is an ideal situation, given that most conversion tools are throw-away
       (use once, and never look back).

PARALLEL OPERATION
       Like git push or git fetch, imports handled by fast-import are safe to run alongside
       parallel git repack -a -d or git gc invocations, or any other Git operation (including git
       prune, as loose objects are never used by fast-import).

       fast-import does not lock the branch or tag refs it is actively importing. After the
       import, during its ref update phase, fast-import tests each existing branch ref to verify
       the update will be a fast-forward update (the commit stored in the ref is contained in the
       new history of the commit to be written). If the update is not a fast-forward update,
       fast-import will skip updating that ref and instead prints a warning message. fast-import
       will always attempt to update all branch refs, and does not stop on the first failure.

       Branch updates can be forced with --force, but it’s recommended that this only be used on
       an otherwise quiet repository. Using --force is not necessary for an initial import into
       an empty repository.

TECHNICAL DISCUSSION
       fast-import tracks a set of branches in memory. Any branch can be created or modified at
       any point during the import process by sending a commit command on the input stream. This
       design allows a frontend program to process an unlimited number of branches
       simultaneously, generating commits in the order they are available from the source data.
       It also simplifies the frontend programs considerably.

       fast-import does not use or alter the current working directory, or any file within it.
       (It does however update the current Git repository, as referenced by GIT_DIR.) Therefore
       an import frontend may use the working directory for its own purposes, such as extracting
       file revisions from the foreign source. This ignorance of the working directory also
       allows fast-import to run very quickly, as it does not need to perform any costly file
       update operations when switching between branches.

INPUT FORMAT
       With the exception of raw file data (which Git does not interpret) the fast-import input
       format is text (ASCII) based. This text based format simplifies development and debugging
       of frontend programs, especially when a higher level language such as Perl, Python or Ruby
       is being used.

       fast-import is very strict about its input. Where we say SP below we mean exactly one
       space. Likewise LF means one (and only one) linefeed and HT one (and only one) horizontal
       tab. Supplying additional whitespace characters will cause unexpected results, such as
       branch names or file names with leading or trailing spaces in their name, or early
       termination of fast-import when it encounters unexpected input.

   Stream Comments
       To aid in debugging frontends fast-import ignores any line that begins with # (ASCII
       pound/hash) up to and including the line ending LF. A comment line may contain any
       sequence of bytes that does not contain an LF and therefore may be used to include any
       detailed debugging information that might be specific to the frontend and useful when
       inspecting a fast-import data stream.

   Date Formats
       The following date formats are supported. A frontend should select the format it will use
       for this import by passing the format name in the --date-format= command-line option.

       raw
           This is the Git native format and is 

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