GIT-FAST-IMPORT(1)                                          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
       --date-format=<fmt>
              Specify the type of dates the frontend will supply to
              fast-import within author, committer and tagger commands. See
              &#8220;Date Formats&#8221; below for details about which formats
              are supported, and their syntax.


       --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).


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


       --big-file-threshold=<n>
              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=<n>
              Maximum delta depth, for blob and tree deltification. Default is
              10.


       --active-branches=<n>
              Maximum number of branches to maintain active at once. See
              &#8220;Memory Utilization&#8221; below for details. Default is
              5.


       --export-marks=<file>
              Dumps the internal marks table to <file> 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 <file> is
              only opened and truncated at checkpoint (or completion) the same
              path can also be safely given to --import-marks.


       --import-marks=<file>
              Before processing any input, load the marks specified in <file>.
              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=<file>
              Like --import-marks but instead of erroring out, silently skips
              the file if it does not exist.


       --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.


       --no-relative-marks
              Negates a previous --relative-marks. Allows for combining
              relative and non-relative marks by interweaving
              --(no-)-relative-marks with the --(import|export)-marks=
              options.


       --cat-blob-fd=<fd>
              Specify the file descriptor that will be written to when the
              cat-blob command is encountered in the stream. The default
              behaviour is to write to stdout.


       --export-pack-edges=<file>
              After creating a packfile, print a line of data to <file>
              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.


       --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.


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&#8217;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=<fmt> command line option.


       raw    This is the Git native format and is <time> SP <offutc>. It is
              also fast-import&#8217;s default format, if --date-format was
              not specified.

              The time of the event is specified by <time> as the number of
              seconds since the UNIX epoch (midnight, Jan 1, 1970, UTC) and is
              written as an ASCII decimal integer.

              The local offset is specified by <offutc> as a positive or
              negative offset from UTC. For example EST (which is 5 hours
              behind UTC) would be expressed in <tz> by &#8220;-0500&#8221;
              while UTC is &#8220;+0000&#8221;. The local offset does not
              affect <time>; it is used only as an advisement to help
              formatting routines display the timestamp.

              If the local offset is not available in the source material, use
              &#8220;+0000&#8221;, or the most common local offset. For
              example many organizations have a CVS repository which has only
              ever been accessed by users who are located in the same location
              and timezone. In this case a reasonable offset from UTC could be
              assumed.

              Unlike the rfc2822 format, this format is very strict. Any
              variation in formatting will cause fast-import to reject the
              value.


       rfc2822
              This is the standard email format as described by RFC 2822.

              An example value is &#8220;Tue Feb 6 11:22:18 2007 -0500&#8221;.
              The Git parser is accurate, but a little on the lenient side. It
              is the same parser used by git am when applying patches received
              from email.

              Some malformed strings may be accepted as valid dates. In some
              of these cases Git will still be able to obtain the correct date
              from the malformed string. There are also some types of
              malformed strings which Git will parse wrong, and yet consider
              valid. Seriously malformed strings will be rejected.

              Unlike the raw format above, the timezone/UTC offset information
              contained in an RFC 2822 date string is used to adjust the date
              value to UTC prior to storage. Therefore it is important that
              this information be as accurate as possible.

              If the source material uses RFC 2822 style dates, the frontend
              should let fast-import handle the parsing and conversion (rather
              than attempting to do it itself) as the Git parser has been well
              tested in the wild.

              Frontends should prefer the raw format if the source material
              already uses UNIX-epoch format, can be coaxed to give dates in
              that format, or its format is easily convertible to it, as there
              is no ambiguity in parsing.


       now    Always use the current time and timezone. The literal now must
              always be supplied for <when>.

              This is a toy format. The current time and timezone of this
              system is always copied into the identity string at the time it
              is being created by fast-import. There is no way to specify a
              different time or timezone.

              This particular format is supplied as it&#8217;s short to
              implement and may be useful to a process that wants to create a
              new commit right now, without needing to use a working directory
              or git update-index.

              If separate author and committer commands are used in a commit
              the timestamps may not match, as the system clock will be polled
              twice (once for each command). The only way to ensure that both
              author and committer identity information has the same timestamp
              is to omit author (thus copying from committer) or to use a date
              format other than now.


   Commands
       fast-import accepts several commands to update the current repository
       and control the current import process. More detailed discussion (with
       examples) of each command follows later.


       commit Creates a new branch or updates an existing branch by creating a
              new commit and updating the branch to point at the newly created
              commit.


       tag    Creates an annotated tag object from an existing commit or
              branch. Lightweight tags are not supported by this command, as
              they are not recommended for recording meaningful points in
              time.


       reset  Reset an existing branch (or a new branch) to a specific
              revision. This command must be used to change a branch to a
              specific revision without making a commit on it.


       blob   Convert raw file data into a blob, for future use in a commit
              command. This command is optional and is not needed to perform
              an import.


       checkpoint
              Forces fast-import to close the current packfile, generate its
              unique SHA-1 checksum and index, and start a new packfile. This
              command is optional and is not needed to perform an import.


       progress
              Causes fast-import to echo the entire line to its own standard
              output. This command is optional and is not needed to perform an
              import.


       cat-blob
              Causes fast-import to print a blob in cat-file --batch format to
              the file descriptor set with --cat-blob-fd or stdout if
              unspecified.


       ls     Causes fast-import to print a line describing a directory entry
              in ls-tree format to the file descriptor set with --cat-blob-fd
              or stdout if unspecified.


       feature
              Require that fast-import supports the specified feature, or
              abort if it does not.


       option Specify any of the options listed under OPTIONS that do not
              change stream semantic to suit the frontend&#8217;s needs. This
              command is optional and is not needed to perform an import.


   commit
       Create or update a branch with a new commit, recording one logical
       change to the project.

               'commit' SP <ref> LF
               mark?
               ('author' (SP <name>)? SP LT <email> GT SP <when> LF)?
               'committer' (SP <name>)? SP LT <email> GT SP <when> LF
               data
               ('from' SP <committish> LF)?
               ('merge' SP <committish> LF)?
               (filemodify | filedelete | filecopy | filerename | filedeleteall | notemodify)*
               LF?


       where <ref> is the name of the branch to make the commit on. Typically
       branch names are prefixed with refs/heads/ in Git, so importing the CVS
       branch symbol RELENG-1_0 would use refs/heads/RELENG-1_0 for the value
       of <ref>. The value of <ref> must be a valid refname in Git. As LF is
       not valid in a Git refname, no quoting or escaping syntax is supported
       here.


       A mark command may optionally appear, requesting fast-import to save a
       reference to the newly created commit for future use by the frontend
       (see below for format). It is very common for frontends to mark every
       commit they create, thereby allowing future branch creation from any
       imported commit.


       The data command following committer must supply the commit message
       (see below for data command syntax). To import an empty commit message
       use a 0 length data. Commit 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.


       Zero or more filemodify, filedelete, filecopy, filerename,
       filedeleteall and notemodify commands may be included to update the
       contents of the branch prior to creating the commit. These commands may
       be supplied in any order. However it is recommended that a
       filedeleteall command precede all filemodify, filecopy, filerename and
       notemodify commands in the same commit, as filedeleteall wipes the
       branch clean (see below).


       The LF after the command is optional (it used to be required).


       An author command may optionally appear, if the author information
       might differ from the committer information. If author is omitted then
       fast-import will automatically use the committer&#8217;s information
       for the author portion of the commit. See below for a description of
       the fields in author, as they are identical to committer.


       The committer command indicates who made this commit, and when they
       made it.


       Here <name> is the person&#8217;s display name (for example &#8220;Com
       M Itter&#8221;) and <email> is the person&#8217;s email address
       (&#8220;cm@example.com: mailto:cm@example.com&#8221;). LT and GT are
       the literal less-than (\x3c) and greater-than (\x3e) symbols. These are
       required to delimit the email address from the other fields in the
       line. Note that <name> is free-form and may contain any sequence of
       bytes, except LT and LF. It is typically UTF-8 encoded.


       The time of the change is specified by <when> using the date format
       that was selected by the --date-format=<fmt> command line option. See
       &#8220;Date Formats&#8221; above for the set of supported formats, and
       their syntax.


       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 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:


       o  The name of an existing branch already in fast-import&#8217;s
          internal branch table. If fast-import doesn&#8217;t know the name,
          it&#8217;s treated as a SHA-1 expression.

       o  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.

       o  A complete 40 byte or abbreviated commit SHA-1 in hex.

       o  Any valid Git SHA-1 expression that resolves to a commit. See
          &#8220;SPECIFYING REVISIONS&#8221; in 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 ^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 ^0 will force fast-import
       to resolve the commit through Git&#8217;s revision parsing library,
       rather than its internal branch table, thereby loading in the existing
       value of the branch.


       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&#8217;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).


       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:


       o
           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.

       o
           100755 or 755: A normal, but executable, file.

       o
           120000: A symlink, the content of the file will be the link target.

       o
           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.

       o
           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:


       o  contain an empty directory component (e.g. foo//bar is invalid),

       o  end with a directory separator (e.g. foo/ is invalid),

       o  start with a directory separator (e.g. /foo is invalid),

       o  contain the special component . or .. (e.g. foo/./bar and foo/../bar
          are invalid).

       The root of the tree can be represented by an empty string as <path>.


       It is recommended that <path> always be encoded using UTF-8.


       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>.


       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.


       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&#8217;t
       want bother with decomposing it into a filecopy followed by a
       filedelete.


       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.


       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&#8217;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&#8217;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.


   cat-blob
       Causes fast-import to print a blob to a file descriptor previously
       arranged with the --cat-blob-fd argument. The command otherwise has no
       impact on the current import; its main purpose is to retrieve blobs
       that may be in fast-import&#8217;s memory but not accessible from the
       target repository.

               'cat-blob' SP <dataref> LF


       The <dataref> can be either a mark reference (:<idnum>) set previously
       or a full 40-byte SHA-1 of a Git blob, preexisting or ready to be
       written.


       Output uses the same format as git cat-file --batch:


              <sha1> SP 'blob' SP <size> LF
              <contents> LF


              This command can be used anywhere in the stream that comments
              are accepted. In particular, the cat-blob command can be used in
              the middle of a commit but not in the middle of a data command.


   ls
       Prints information about the object at a path to a file descriptor
       previously arranged with the --cat-blob-fd argument. This allows
       printing a blob from the active commit (with cat-blob) or copying a
       blob or tree from a previous commit for use in the current one (with
       filemodify).


       The ls command can be used anywhere in the stream that comments are
       accepted, including the middle of a commit.


       Reading from the active commit
              This form can only be used in the middle of a commit. The path
              names a directory entry within fast-import&#8217;s active
              commit. The path must be quoted in this case.

                      'ls' SP <path> LF


       Reading from a named tree
              The <dataref> can be a mark reference (:<idnum>) or the full
              40-byte SHA-1 of a Git tag, commit, or tree object, preexisting
              or waiting to be written. The path is relative to the top level
              of the tree named by <dataref>.

                      'ls' SP <dataref> SP <path> LF


              See filemodify above for a detailed description of <path>.


              Output uses the same format as git ls-tree <tree> -- <path>:


              <mode> SP ('blob' | 'tree' | 'commit') SP <dataref> HT <path> LF


              The <dataref> represents the blob, tree, or commit object at
              <path> and can be used in later cat-blob, filemodify, or ls
              commands.


              If there is no file or subtree at that path, git fast-import
              will instead report


              missing SP <path> LF


   feature
       Require that fast-import supports the specified feature, or abort if it
       does not.

               'feature' SP <feature> ('=' <argument>)? LF


       The <feature> part of the command may be any one of the following:


       date-format, export-marks, relative-marks, no-relative-marks, force
              Act as though the corresponding command-line option with a
              leading -- was passed on the command line (see OPTIONS, above).


       import-marks
              Like --import-marks except in two respects: first, only one
              "feature import-marks" command is allowed per stream; second, an
              --import-marks= command-line option overrides any "feature
              import-marks" command in the stream.


       cat-blob, ls
              Require that the backend support the cat-blob or ls command.
              Versions of fast-import not supporting the specified command
              will exit with a message indicating so. This lets the import
              error out early with a clear message, rather than wasting time
              on the early part of an import before the unsupported command is
              detected.


       notes  Require that the backend support the notemodify (N) subcommand
              to the commit command. Versions of fast-import not supporting
              notes will exit with a message indicating so.


   option
       Processes the specified option so that git fast-import behaves in a way
       that suits the frontend&#8217;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:


       o  date-format

       o  import-marks

       o  export-marks

       o  cat-blob-fd

       o  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&#8217;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 &#8220;fixes up&#8221; the files to match the content
       of the tag. Use fast-import&#8217;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&#8217;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
       Every once in a while have your frontend emit a progress message to
       fast-import. The contents of the messages are entirely free-form, so
       one suggestion would be to output the current month and year each time
       the current commit date moves into the next month. Your users will feel
       better knowing how much of the data stream has been processed.


PACKFILE OPTIMIZATION
       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.


       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.


       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.


       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).


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 &#8220;per active file&#8221;
       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
       &#8220;Makefile&#8221; 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).


SIGNALS
       Sending SIGUSR1 to the git fast-import process ends the current
       packfile early, simulating a checkpoint command. The impatient operator
       can use this facility to peek at the objects and refs from an import in
       progress, at the cost of some added running time and worse compression.


GIT
       Part of the git(1) suite




                                                            GIT-FAST-IMPORT(1)
