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GIT-FAST-IMPORT(1) Git Manual GIT-FAST-IMPORT(1)
git-fast-import - Backend for fast Git data importers
frontend | git fast-import [<options>]
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.
--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)
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).
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).
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.
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.
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
('encoding' SP <encoding>)?
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.
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.
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.
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
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.
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.
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).
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.
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-fast-export(1)
Part of the git(1) suite
This page is part of the git (Git distributed version control
system) project. Information about the project can be found at
⟨http://git-scm.com/⟩. If you have a bug report for this manual
page, see ⟨http://git-scm.com/community⟩. This page was obtained
from the project's upstream Git repository
⟨https://github.com/git/git.git⟩ on 2024-06-14. (At that time,
the date of the most recent commit that was found in the
repository was 2024-06-12.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
Git 2.45.2.492.gd63586 2024-06-12 GIT-FAST-IMPORT(1)
Pages that refer to this page: git(1), git-config(1), git-fast-export(1), git-fast-import(1), git-gc(1), githooks(5), gitremote-helpers(7)
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