# git-fast-import

## 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 the output shown by --stats, making fast-import
               usually be silent when it is successful. However, if the
               import stream has directives intended to show user output
               (e.g.  **progress** directives), the corresponding messages will
               still be shown.
    
           --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.
    
           --allow-unsafe-features
               Many command-line options can be provided as part of the
               fast-import stream itself by using the **feature** or **option**
               commands. However, some of these options are unsafe (e.g.,
               allowing fast-import to access the filesystem outside of the
               repository). These options are disabled by default, but can be
               allowed by providing this option on the command line. This
               currently impacts only the **export-marks** , **import-marks** , and
               **import-marks-if-exists** feature commands.
    
                   Only enable this option if you trust the program generating the
                   fast-import stream! This option is enabled automatically for
                   remote-helpers that use the `import` capability, as they are
                   already trusted to run their own code.
    
       **Options for Frontends**
           --cat-blob-fd=<fd>
               Write responses to **get-mark** , **cat-blob** , and **ls** queries to the
               file descriptor <fd> instead of **stdout**. Allows **progress** output
               intended for the end-user to be separated from other output.
    
           --date-format=<fmt>
               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=<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.
    
           --[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.
    
       **Submodule Rewriting**
           --rewrite-submodules-from=<name>:<file>,
           --rewrite-submodules-to=<name>:<file>
               Rewrite the object IDs for the submodule specified by <name>
               from the values used in the from <file> to those used in the
               to <file>. The from marks should have been created by **git**
               **fast-export** , and the to marks should have been created by **git**
               **fast-import** when importing that same submodule.
    
               <name> may be any arbitrary string not containing a colon
               character, but the same value must be used with both options
               when specifying corresponding marks. Multiple submodules may
               be specified with different values for <name>. It is an error
               not to use these options in corresponding pairs.
    
               These options are primarily useful when converting a
               repository from one hash algorithm to another; without them,
               fast-import will fail if it encounters a submodule because it
               has no way of writing the object ID into the new hash
               algorithm.
    
       **Performance and Compression Tuning**
           --active-branches=<n>
               Maximum number of branches to maintain active at once. See
               “Memory Utilization” below for details. Default is 5.
    
           --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 50.
    
           --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_.
    
           --max-pack-size=<n>
               Maximum size of each output packfile. The default is
               unlimited.
    
           fastimport.unpackLimit
               See git-config(1)
    


## 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 hardware
           (~$2,000 USD in 2007).
    
           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=<fmt> command-line option.
    
           **raw**
               This is the Git native format and is _< time>_ **SP** _< offutc>_. It is
               also fast-import’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 “-0500” while UTC is
               “+0000”. 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 “+0000”, 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
               time zone. 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, and some sanity checks on the numeric values may also
               be performed.
    
           **raw-permissive**
               This is the same as **raw** except that no sanity checks on the
               numeric epoch and local offset are performed. This can be
               useful when trying to filter or import an existing history
               with e.g. bogus timezone values.
    
           **rfc2822**
               This is the standard date format as described by RFC 2822.
    
               An example value is “Tue Feb 6 11:22:18 2007 -0500”. 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 time zone/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 time zone. The literal **now**
               must always be supplied for _< when>_.
    
               This is a toy format. The current time and time zone 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 time zone.
    
               This particular format is supplied as it’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.
    
           **alias**
               Record that a mark refers to a given object without first
               creating any new object. Using --import-marks and referring to
               missing marks will cause fast-import to fail, so aliases can
               provide a way to set otherwise pruned commits to a valid value
               (e.g. the nearest non-pruned ancestor).
    
           **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.
    
           **done**
               Marks the end of the stream. This command is optional unless
               the **done** feature was requested using the **--done** command-line
               option or **feature done** command.
    
           **get-mark**
               Causes fast-import to print the SHA-1 corresponding to a mark
               to the file descriptor set with **--cat-blob-fd** , or **stdout** if
               unspecified.
    
           **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**
               Enable the specified feature. This requires that fast-import
               supports the specified feature, and aborts if it does not.
    
           **option**
               Specify any of the options listed under OPTIONS that do not
               change stream semantic to suit the frontend’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?
                       original-oid?
                       ('author' (SP <name>)? SP LT <email> GT SP <when> LF)?
                       'committer' (SP <name>)? SP LT <email> GT SP <when> LF
                       ('gpgsig' SP <algo> SP <format> LF data)?
                       ('encoding' SP <encoding> LF)?
                       data
                       ('from' SP <commit-ish> LF)?
                       ('merge' SP <commit-ish> 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).
           Note that for reasons of backward compatibility, if the commit
           ends with a **data** command (i.e. it has no **from** , **merge** , **filemodify** ,
           **filedelete** , **filecopy** , **filerename** , **filedeleteall** or **notemodify**
           commands) then two **LF** commands may appear at the end of the
           command instead of just one.
    
           **author**
    
               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’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**.
    
           **committer**
    
               The **committer** command indicates who made this commit, and when
               they made it.
    
               Here _< name>_ is the person’s display name (for example “Com M
               Itter”) and _< email>_ is the person’s email address
               (“cm@example.com”). **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>_ and _< email>_ are free-form and may contain any sequence
               of bytes, except **LT** , **GT** and **LF**. _< name>_ 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 “Date Formats” above for the set of
               supported formats, and their syntax.
    
           **gpgsig**
    
               The optional **gpgsig** command is used to include a PGP/GPG
               signature or other cryptographic signature that signs the
               commit data.
    
                           'gpgsig' SP <git-hash-algo> SP <signature-format> LF data
    
               The **gpgsig** command takes two arguments:
    
               •   _< git-hash-algo>_ specifies which Git object format this
                   signature applies to, either **sha1** or **sha256**. This allows
                   to know which representation of the commit was signed (the
                   SHA-1 or the SHA-256 version) which helps with both
                   signature verification and interoperability between repos
                   with different hash functions.
    
               •   _< signature-format>_ specifies the type of signature, such
                   as **openpgp** , **x509** , **ssh** , or **unknown**. This is a convenience
                   for tools that process the stream, so they don’t have to
                   parse the ASCII armor to identify the signature type.
    
               A commit may have at most one signature for the SHA-1 object
               format (stored in the "gpgsig" header) and one for the SHA-256
               object format (stored in the "gpgsig-sha256" header).
    
               See below for a detailed description of the **data** command which
               contains the raw signature data.
    
               Signatures are not yet checked in the current implementation
               though. (Already setting the **extensions.compatObjectFormat**
               configuration option might help with verifying both SHA-1 and
               SHA-256 object format signatures when it will be implemented.)
    
                   **Note**
    
                   This is highly experimental and the format of the **gpgsig**
                   command may change in the future without compatibility
                   guarantees.
    
           **encoding**
    
               The optional **encoding** command indicates the encoding of the
               commit message. Most commits are UTF-8 and the encoding is
               omitted, but this allows importing commit messages into git
               without first reencoding them.
    
           **from**
    
               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. The state of the tree built at this commit
               will begin with the state at the **from** commit, and be altered
               by the content modifications in this 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 _< commit-ish>_.
    
               Here _< commit-ish>_ is any of the following:
    
               •   The name of an existing branch already in fast-import’s
                   internal branch table. If fast-import doesn’t know the
                   name, it’s treated as a SHA-1 expression.
    
               •   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 gitrevisions(7) for details.
    
               •   The special null SHA-1 (40 zeros) specifies that the
                   branch is to be removed.
    
               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’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. The additional
               ancestry link does not change the way the tree state is built
               at this 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.
    
               Here _< commit-ish>_ 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
                   either 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>_ can be written as unquoted bytes or a C-style quoted
               string.
    
               When a _< path>_ does not start with a double quote ("), it is an
               unquoted string and is parsed as literal bytes without any
               escape sequences. However, if the filename contains **LF** or
               starts with double quote, it cannot be represented as an
               unquoted string and must be quoted. Additionally, the source
               _< path>_ in **filecopy** or **filerename** must be quoted if it contains
               SP.
    
               When a _< path>_ starts with a double quote ("), it is a C-style
               quoted string, where the complete filename is enclosed in a
               pair of double quotes and escape sequences are used. Certain
               characters must be escaped by preceding them with a backslash:
               **LF** is written as **\n** , backslash as **\\** , and double quote as **\** ".
               Some characters may optionally be written with escape
               sequences: **\a** for bell, **\b** for backspace, **\f** for form feed, **\n**
               for line feed, **\r** for carriage return, **\t** for horizontal tab,
               and **\v** for vertical tab. Any byte can be written with 3-digit
               octal codes (e.g., **\033**). All filenames can be represented as
               quoted strings.
    
               A _< path>_ must use UNIX-style directory separators (forward
               slash **/**) and its value 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).
    
               The root of the tree can be represented by an empty string as
               _< path>_.
    
               _< path>_ cannot contain NUL, either literally or escaped as
               **\000**. 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** _< notes-ref>_ command to add a new note
               annotating a _< commit-ish>_ or change this annotation contents.
               Internally it is similar to filemodify 100644 on _< commit-ish>_
               path (maybe split into subdirectories). It’s not advised to
               use any other commands to write to the _< notes-ref>_ tree except
               **filedeleteall** to delete all existing notes in this tree. 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 <commit-ish> 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 <commit-ish> LF
                               data
    
                   See below for a detailed description of the **data** command.
    
               In both formats _< commit-ish>_ 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.
    
       **original-oid**
           Provides the name of the object in the original source control
           system. fast-import will simply ignore this directive, but filter
           processes which operate on and modify the stream before feeding to
           fast-import may have uses for this information
    
                       'original-oid' SP <object-identifier> LF
    
           where _< object-identifier>_ is any string not containing LF.
    
       **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
                       mark?
                       'from' SP <commit-ish> LF
                       original-oid?
                       '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 <commit-ish> LF)?
                       LF?
    
           For a detailed description of _< ref>_ and _< commit-ish>_ 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?
                       original-oid?
                       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).
    
       **alias**
           Record that a mark refers to a given object without first creating
           any new object.
    
                       'alias' LF
                       mark
                       'to' SP <commit-ish> LF
                       LF?
    
           For a detailed description of _< commit-ish>_ see above under **from**.
    
       **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.
    
       **get-mark**
           Causes fast-import to print the SHA-1 corresponding to a mark to
           stdout or to the file descriptor previously arranged with the
           **--cat-blob-fd** argument. The command otherwise has no impact on the
           current import; its purpose is to retrieve SHA-1s that later
           commits might want to refer to in their commit messages.
    
                       'get-mark' SP ':' <idnum> LF
    
           See “Responses To Commands” below for details about how to read
           this output safely.
    
       **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’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 where a **filemodify** directive can appear,
           allowing it to be used in the middle of a commit. For a **filemodify**
           using an inline directive, it can also appear right before the
           **data** directive.
    
           See “Responses To Commands” below for details about how to read
           this output safely.
    
       **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 also be used where a **filemodify** directive can
           appear, allowing it to be used in 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’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 _get-mark_ , _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
    
           See “Responses To Commands” below for details about how to read
           this output safely.
    
       **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, import-marks-if-exists
               Like --import-marks except in two respects: first, only one
               "feature import-marks" or "feature import-marks-if-exists"
               command is allowed per stream; second, an --import-marks= or
               --import-marks-if-exists command-line option overrides any of
               these "feature" commands in the stream; third, "feature
               import-marks-if-exists" like a corresponding command-line
               option silently skips a nonexistent file.
    
           get-mark, cat-blob, ls
               Require that the backend support the _get-mark_ , _cat-blob_ , or _ls_
               command respectively. 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.
    
           done
               Error out if the stream ends without a _done_ command. Without
               this feature, errors causing the frontend to end abruptly at a
               convenient point in the stream can go undetected. This may
               occur, for example, if an import front end dies in
               mid-operation without emitting SIGTERM or SIGKILL at its
               subordinate git fast-import instance.
    
       **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 command-line options change import semantics and may
           therefore not be passed as option:
    
           •   date-format
    
           •   import-marks
    
           •   export-marks
    
           •   cat-blob-fd
    
           •   force
    
       **done**
           If the **done** feature is not in use, treated as if EOF was read.
           This can be used to tell fast-import to finish early.
    
           If the **--done** command-line option or **feature done** command is in
           use, the **done** command is mandatory and marks the end of the
           stream.
    


## RESPONSES TO COMMANDS



           New objects written by fast-import are not available immediately.
           Most fast-import commands have no visible effect until the next
           checkpoint (or completion). The frontend can send commands to fill
           fast-import’s input pipe without worrying about how quickly they
           will take effect, which improves performance by simplifying
           scheduling.
    
           For some frontends, though, it is useful to be able to read back
           data from the current repository as it is being updated (for
           example when the source material describes objects in terms of
           patches to be applied to previously imported objects). This can be
           accomplished by connecting the frontend and fast-import via
           bidirectional pipes:
    
               mkfifo fast-import-output
               frontend <fast-import-output |
               git fast-import >fast-import-output
    
           A frontend set up this way can use **progress** , **get-mark** , **ls** , and
           **cat-blob** commands to read information from the import in progress.
    
           To avoid deadlock, such frontends must completely consume any
           pending output from **progress** , **ls** , **get-mark** , and **cat-blob** before
           performing writes to fast-import that might block.
    


## 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**
           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).
    
           Instead of running **git repack** you can also run **git gc**
           **--aggressive** , which will also optimize other things after an
           import (e.g. pack loose refs). As noted in the "AGGRESSIVE"
           section in git-gc(1) the **--aggressive** option will find new deltas
           with the **-f** option to git-repack(1). For the reasons elaborated on
           above using **--aggressive** after a fast-import is one of the few
           cases where it’s known to be worthwhile.
    


## 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).
    


## 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.
    


## CONFIGURATION



           Everything below this line in this section is selectively included
           from the git-config(1) documentation. The content is the same as
           what’s found there:
    
           fastimport.unpackLimit
               If the number of objects imported by git-fast-import(1) is
               below this limit, then the objects will be unpacked into loose
               object files. However, if the number of imported objects
               equals or exceeds this limit, then the pack will be stored as
               a pack. Storing the pack from a fast-import can make the
               import operation complete faster, especially on slow
               filesystems. If not set, the value of **transfer.unpackLimit** is
               used instead.
    


## GIT



           Part of the git(1) suite
    


* * *