git-fast-import
(1)
名前
git-fast-import - Backend for fast Git data importers
形式
frontend | git fast-import [options]
説明
Git Manual GIT-FAST-IMPORT(1)
NAME
git-fast-import - Backend for fast Git data importers
SYNOPSIS
frontend | git fast-import [options]
DESCRIPTION
This program is usually not what the end user wants to run
directly. Most end users want to use one of the existing
frontend programs, which parses a specific type of foreign
source and feeds the contents stored there to git
fast-import.
fast-import reads a mixed command/data stream from standard
input and writes one or more packfiles directly into the
current repository. When EOF is received on standard input,
fast import writes out updated branch and tag refs, fully
updating the current repository with the newly imported
data.
The fast-import backend itself can import into an empty
repository (one that has already been initialized by git
init) or incrementally update an existing populated
repository. Whether or not incremental imports are supported
from a particular foreign source depends on the frontend
program in use.
OPTIONS
--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.
--force
Force updating modified existing branches, even if doing
so would cause commits to be lost (as the new commit
does not contain the old commit).
--max-pack-size=<n>
Maximum size of each output packfile. The default is
unlimited.
--big-file-threshold=<n>
Maximum size of a blob that fast-import will attempt to
create a delta for, expressed in bytes. The default is
512m (512 MiB). Some importers may wish to lower this on
systems with constrained memory.
--depth=<n>
Maximum delta depth, for blob and tree deltification.
Git 1.7.9.2 Last change: 02/22/2012 1
Git Manual GIT-FAST-IMPORT(1)
Default is 10.
--active-branches=<n>
Maximum number of branches to maintain active at once.
See "Memory Utilization" below for details. Default is
5.
--export-marks=<file>
Dumps the internal marks table to <file> when complete.
Marks are written one per line as :markid SHA-1.
Frontends can use this file to validate imports after
they have been completed, or to save the marks table
across incremental runs. As <file> is only opened and
truncated at checkpoint (or completion) the same path
can also be safely given to --import-marks.
--import-marks=<file>
Before processing any input, load the marks specified in
<file>. The input file must exist, must be readable, and
must use the same format as produced by --export-marks.
Multiple options may be supplied to import more than one
set of marks. If a mark is defined to different values,
the last file wins.
--import-marks-if-exists=<file>
Like --import-marks but instead of erroring out,
silently skips the file if it does not exist.
--relative-marks
After specifying --relative-marks the paths specified
with --import-marks= and --export-marks= are relative to
an internal directory in the current repository. In
git-fast-import this means that the paths are relative
to the .git/info/fast-import directory. However, other
importers may use a different location.
--no-relative-marks
Negates a previous --relative-marks. Allows for
combining relative and non-relative marks by
interweaving --(no-)-relative-marks with the
--(import|export)-marks= options.
--cat-blob-fd=<fd>
Specify the file descriptor that will be written to when
the cat-blob command is encountered in the stream. The
default behaviour is to write to stdout.
--done
Require a 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.
Git 1.7.9.2 Last change: 02/22/2012 2
Git Manual GIT-FAST-IMPORT(1)
--export-pack-edges=<file>
After creating a packfile, print a line of data to
<file> listing the filename of the packfile and the last
commit on each branch that was written to that packfile.
This information may be useful after importing projects
whose total object set exceeds the 4 GiB packfile limit,
as these commits can be used as edge points during calls
to git pack-objects.
--quiet
Disable all non-fatal output, making fast-import silent
when it is successful. This option disables the output
shown by --stats.
--stats
Display some basic statistics about the objects
fast-import has created, the packfiles they were stored
into, and the memory used by fast-import during this
run. Showing this output is currently the default, but
can be disabled with --quiet.
PERFORMANCE
The design of fast-import allows it to import large projects
in a minimum amount of memory usage and processing time.
Assuming the frontend is able to keep up with fast-import
and feed it a constant stream of data, import times for
projects holding 10+ years of history and containing
100,000+ individual commits are generally completed in just
1-2 hours on quite modest (~$2,000 USD) hardware.
Most bottlenecks appear to be in foreign source data access
(the source just cannot extract revisions fast enough) or
disk IO (fast-import writes as fast as the disk will take
the data). Imports will run faster if the source data is
stored on a different drive than the destination Git
repository (due to less IO contention).
DEVELOPMENT COST
A typical frontend for fast-import tends to weigh in at
approximately 200 lines of Perl/Python/Ruby code. Most
developers have been able to create working importers in
just a couple of hours, even though it is their first
exposure to fast-import, and sometimes even to Git. This is
an ideal situation, given that most conversion tools are
throw-away (use once, and never look back).
PARALLEL OPERATION
Like git push or git fetch, imports handled by fast-import
are safe to run alongside parallel git repack -a -d or git
gc invocations, or any other Git operation (including git
prune, as loose objects are never used by fast-import).
Git 1.7.9.2 Last change: 02/22/2012 3
Git Manual GIT-FAST-IMPORT(1)
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
Git 1.7.9.2 Last change: 02/22/2012 4
Git Manual GIT-FAST-IMPORT(1)
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 timezone. In this case
a reasonable offset from UTC could be assumed.
Unlike the rfc2822 format, this format is very strict.
Any variation in formatting will cause fast-import to
reject the value.
rfc2822
This is the standard email format as described by RFC
2822.
An example value is "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
Git 1.7.9.2 Last change: 02/22/2012 5
Git Manual GIT-FAST-IMPORT(1)
parse wrong, and yet consider valid. Seriously malformed
strings will be rejected.
Unlike the raw format above, the timezone/UTC offset
information contained in an RFC 2822 date string is used
to adjust the date value to UTC prior to storage.
Therefore it is important that this information be as
accurate as possible.
If the source material uses RFC 2822 style dates, the
frontend should let fast-import handle the parsing and
conversion (rather than attempting to do it itself) as
the Git parser has been well tested in the wild.
Frontends should prefer the raw format if the source
material already uses UNIX-epoch format, can be coaxed
to give dates in that format, or its format is easily
convertible to it, as there is no ambiguity in parsing.
now
Always use the current time and timezone. The literal
now must always be supplied for <when>.
This is a toy format. The current time and timezone of
this system is always copied into the identity string at
the time it is being created by fast-import. There is no
way to specify a different time or timezone.
This particular format is supplied as it'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.
Git 1.7.9.2 Last change: 02/22/2012 6
Git Manual GIT-FAST-IMPORT(1)
tag
Creates an annotated tag object from an existing commit
or branch. Lightweight tags are not supported by this
command, as they are not recommended for recording
meaningful points in time.
reset
Reset an existing branch (or a new branch) to a specific
revision. This command must be used to change a branch
to a specific revision without making a commit on it.
blob
Convert raw file data into a blob, for future use in a
commit command. This command is optional and is not
needed to perform an import.
checkpoint
Forces fast-import to close the current packfile,
generate its unique SHA-1 checksum and index, and start
a new packfile. This command is optional and is not
needed to perform an import.
progress
Causes fast-import to echo the entire line to its own
standard output. This command is optional and is not
needed to perform an import.
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.
cat-blob
Causes fast-import to print a blob in cat-file --batch
format to the file descriptor set with --cat-blob-fd or
stdout if unspecified.
ls
Causes fast-import to print a line describing a
directory entry in ls-tree format to the file descriptor
set with --cat-blob-fd or stdout if unspecified.
feature
Require that fast-import supports the specified feature,
or abort if it does not.
option
Specify any of the options listed under OPTIONS that do
not change stream semantic to suit the frontend's needs.
This command is optional and is not needed to perform an
import.
Git 1.7.9.2 Last change: 02/22/2012 7
Git Manual GIT-FAST-IMPORT(1)
commit
Create or update a branch with a new commit, recording one
logical change to the project.
'commit' SP <ref> LF
mark?
('author' (SP <name>)? SP LT <email> GT SP <when> LF)?
'committer' (SP <name>)? SP LT <email> GT SP <when> LF
data
('from' SP <committish> LF)?
('merge' SP <committish> LF)?
(filemodify | filedelete | filecopy | filerename | filedeleteall | notemodify)*
LF?
where <ref> is the name of the branch to make the commit on.
Typically branch names are prefixed with refs/heads/ in Git,
so importing the CVS branch symbol RELENG-1_0 would use
refs/heads/RELENG-1_0 for the value of <ref>. The value of
<ref> must be a valid refname in Git. As LF is not valid in
a Git refname, no quoting or escaping syntax is supported
here.
A mark command may optionally appear, requesting fast-import
to save a reference to the newly created commit for future
use by the frontend (see below for format). It is very
common for frontends to mark every commit they create,
thereby allowing future branch creation from any imported
commit.
The data command following committer must supply the commit
message (see below for data command syntax). To import an
empty commit message use a 0 length data. Commit messages
are free-form and are not interpreted by Git. Currently they
must be encoded in UTF-8, as fast-import does not permit
other encodings to be specified.
Zero or more filemodify, filedelete, filecopy, filerename,
filedeleteall and notemodify commands may be included to
update the contents of the branch prior to creating the
commit. These commands may be supplied in any order. However
it is recommended that a filedeleteall command precede all
filemodify, filecopy, filerename and notemodify commands in
the same commit, as filedeleteall wipes the branch clean
(see below).
The LF after the command is optional (it used to be
required).
author
An author command may optionally appear, if the author
information might differ from the committer information.
Git 1.7.9.2 Last change: 02/22/2012 8
Git Manual GIT-FAST-IMPORT(1)
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[1]"). 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.
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.
Omitting the from command in the first commit of a new
branch will cause fast-import to create that commit with
no ancestor. This tends to be desired only for the
initial commit of a project. If the frontend creates all
files from scratch when making a new branch, a merge
command may be used instead of from to start the commit
with an empty tree. Omitting the from command on
existing branches is usually desired, as the current
commit on that branch is automatically assumed to be the
first ancestor of the new commit.
As LF is not valid in a Git refname or SHA-1 expression,
no quoting or escaping syntax is supported within
<committish>.
Here <committish> is any of the following:
o The name of an existing branch already in
fast-import's internal branch table. If fast-import
doesn't know the name, it's treated as a SHA-1
expression.
Git 1.7.9.2 Last change: 02/22/2012 9
Git Manual GIT-FAST-IMPORT(1)
o A mark reference, :<idnum>, where <idnum> is the
mark number.
The reason fast-import uses : to denote a mark
reference is this character is not legal in a Git
branch name. The leading : makes it easy to
distinguish between the mark 42 (:42) and the branch
42 (42 or refs/heads/42), or an abbreviated SHA-1
which happened to consist only of base-10 digits.
Marks must be declared (via mark) before they can be
used.
o A complete 40 byte or abbreviated commit SHA-1 in
hex.
o Any valid Git SHA-1 expression that resolves to a
commit. See "SPECIFYING REVISIONS" in
gitrevisions(5) for details.
The special case of restarting an incremental import
from the current branch value should be written as:
from refs/heads/branch^0
The ^0 suffix is necessary as fast-import does not
permit a branch to start from itself, and the branch is
created in memory before the from command is even read
from the input. Adding ^0 will force fast-import to
resolve the commit through Git's revision parsing
library, rather than its internal branch table, thereby
loading in the existing value of the branch.
merge
Includes one additional ancestor commit. If the from
command is omitted when creating a new branch, the first
merge commit will be the first ancestor of the current
commit, and the branch will start out with no files. An
unlimited number of merge commands per commit are
permitted by fast-import, thereby establishing an n-way
merge. However Git's other tools never create commits
with more than 15 additional ancestors (forming a 16-way
merge). For this reason it is suggested that frontends
do not use more than 15 merge commands per commit; 16,
if starting a new, empty branch.
Here <committish> is any of the commit specification
expressions also accepted by from (see above).
filemodify
Git 1.7.9.2 Last change: 02/22/2012 10
Git Manual GIT-FAST-IMPORT(1)
Included in a commit command to add a new file or change
the content of an existing file. This command has two
different means of specifying the content of the file.
External data format
The data content for the file was already supplied
by a prior blob command. The frontend just needs to
connect it.
'M' SP <mode> SP <dataref> SP <path> LF
Here usually <dataref> must be either a mark
reference (:<idnum>) set by a prior blob command, or
a full 40-byte SHA-1 of an existing Git blob object.
If <mode> is 040000` then <dataref> must be the full
40-byte SHA-1 of an existing Git tree object or a
mark reference set with --import-marks.
Inline data format
The data content for the file has not been supplied
yet. The frontend wants to supply it as part of this
modify command.
'M' SP <mode> SP 'inline' SP <path> LF
data
See below for a detailed description of the data
command.
In both formats <mode> is the type of file entry,
specified in octal. Git only supports the following
modes:
o 100644 or 644: A normal (not-executable) file. The
majority of files in most projects use this mode. If
in doubt, this is what you want.
o 100755 or 755: A normal, but executable, file.
o 120000: A symlink, the content of the file will be
the link target.
o 160000: A gitlink, SHA-1 of the object refers to a
commit in another repository. Git links can only be
specified by SHA or through a commit mark. They are
used to implement submodules.
o 040000: A subdirectory. Subdirectories can only be
specified by SHA or through a tree mark set with
--import-marks.
In both formats <path> is the complete path of the file
Git 1.7.9.2 Last change: 02/22/2012 11
Git Manual GIT-FAST-IMPORT(1)
to be added (if not already existing) or modified (if
already existing).
A <path> string must use UNIX-style directory separators
(forward slash /), may contain any byte other than LF,
and must not start with double quote (").
If an LF or double quote must be encoded into <path>
shell-style quoting should be used, e.g. "path/with\n
and \" in it".
The value of <path> must be in canonical form. That is
it must not:
o contain an empty directory component (e.g. foo//bar
is invalid),
o end with a directory separator (e.g. foo/ is
invalid),
o start with a directory separator (e.g. /foo is
invalid),
o contain the special component . or .. (e.g.
foo/./bar and foo/../bar are invalid).
The root of the tree can be represented by an empty
string as <path>.
It is recommended that <path> always be encoded using
UTF-8.
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
Git 1.7.9.2 Last change: 02/22/2012 12
Git Manual GIT-FAST-IMPORT(1)
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
Git 1.7.9.2 Last change: 02/22/2012 13
Git Manual GIT-FAST-IMPORT(1)
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 <committish> or change this annotation
contents. Internally it is similar to filemodify 100644
on <committish> 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 <committish> LF
Here <dataref> can be either a mark reference
(:<idnum>) set by a prior blob command, or a full
40-byte SHA-1 of an existing Git blob object.
Inline data format
The data content for the note has not been supplied
yet. The frontend wants to supply it as part of this
modify command.
'N' SP 'inline' SP <committish> LF
data
See below for a detailed description of the data
Git 1.7.9.2 Last change: 02/22/2012 14
Git Manual GIT-FAST-IMPORT(1)
command.
In both formats <committish> is any of the commit
specification expressions also accepted by from (see
above).
mark
Arranges for fast-import to save a reference to the current
object, allowing the frontend to recall this object at a
future point in time, without knowing its SHA-1. Here the
current object is the object creation command the mark
command appears within. This can be commit, tag, and blob,
but commit is the most common usage.
'mark' SP ':' <idnum> LF
where <idnum> is the number assigned by the frontend to this
mark. The value of <idnum> is expressed as an ASCII decimal
integer. The value 0 is reserved and cannot be used as a
mark. Only values greater than or equal to 1 may be used as
marks.
New marks are created automatically. Existing marks can be
moved to another object simply by reusing the same <idnum>
in another mark command.
tag
Creates an annotated tag referring to a specific commit. To
create lightweight (non-annotated) tags see the reset
command below.
'tag' SP <name> LF
'from' SP <committish> LF
'tagger' (SP <name>)? SP LT <email> GT SP <when> LF
data
where <name> is the name of the tag to create.
Tag names are automatically prefixed with refs/tags/ when
stored in Git, so importing the CVS branch symbol
RELENG-1_0-FINAL would use just RELENG-1_0-FINAL for <name>,
and fast-import will write the corresponding ref as
refs/tags/RELENG-1_0-FINAL.
The value of <name> must be a valid refname in Git and
therefore may contain forward slashes. As LF is not valid in
a Git refname, no quoting or escaping syntax is supported
here.
The from command is the same as in the commit command; see
above for details.
Git 1.7.9.2 Last change: 02/22/2012 15
Git Manual GIT-FAST-IMPORT(1)
The tagger command uses the same format as committer within
commit; again see above for details.
The data command following tagger must supply the annotated
tag message (see below for data command syntax). To import
an empty tag message use a 0 length data. Tag messages are
free-form and are not interpreted by Git. Currently they
must be encoded in UTF-8, as fast-import does not permit
other encodings to be specified.
Signing annotated tags during import from within fast-import
is not supported. Trying to include your own PGP/GPG
signature is not recommended, as the frontend does not
(easily) have access to the complete set of bytes which
normally goes into such a signature. If signing is required,
create lightweight tags from within fast-import with reset,
then create the annotated versions of those tags offline
with the standard git tag process.
reset
Creates (or recreates) the named branch, optionally starting
from a specific revision. The reset command allows a
frontend to issue a new from command for an existing branch,
or to create a new branch from an existing commit without
creating a new commit.
'reset' SP <ref> LF
('from' SP <committish> LF)?
LF?
For a detailed description of <ref> and <committish> see
above under commit and from.
The LF after the command is optional (it used to be
required).
The reset command can also be used to create lightweight
(non-annotated) tags. For example:
reset refs/tags/938
from :938
would create the lightweight tag refs/tags/938 referring to
whatever commit mark :938 references.
blob
Requests writing one file revision to the packfile. The
revision is not connected to any commit; this connection
must be formed in a subsequent commit command by referencing
the blob through an assigned mark.
'blob' LF
Git 1.7.9.2 Last change: 02/22/2012 16
Git Manual GIT-FAST-IMPORT(1)
mark?
data
The mark command is optional here as some frontends have
chosen to generate the Git SHA-1 for the blob on their own,
and feed that directly to commit. This is typically more
work than it's worth however, as marks are inexpensive to
store and easy to use.
data
Supplies raw data (for use as blob/file content, commit
messages, or annotated tag messages) to fast-import. Data
can be supplied using an exact byte count or delimited with
a terminating line. Real frontends intended for
production-quality conversions should always use the exact
byte count format, as it is more robust and performs better.
The delimited format is intended primarily for testing
fast-import.
Comment lines appearing within the <raw> part of data
commands are always taken to be part of the body of the data
and are therefore never ignored by fast-import. This makes
it safe to import any file/message content whose lines might
start with #.
Exact byte count format
The frontend must specify the number of bytes of data.
'data' SP <count> LF
<raw> LF?
where <count> is the exact number of bytes appearing
within <raw>. The value of <count> is expressed as an
ASCII decimal integer. The LF on either side of <raw> is
not included in <count> and will not be included in the
imported data.
The LF after <raw> is optional (it used to be required)
but recommended. Always including it makes debugging a
fast-import stream easier as the next command always
starts in column 0 of the next line, even if <raw> did
not end with an LF.
Delimited format
A delimiter string is used to mark the end of the data.
fast-import will compute the length by searching for the
delimiter. This format is primarily useful for testing
and is not recommended for real data.
'data' SP '<<' <delim> LF
<raw> LF
<delim> LF
Git 1.7.9.2 Last change: 02/22/2012 17
Git Manual GIT-FAST-IMPORT(1)
LF?
where <delim> is the chosen delimiter string. The string
<delim> must not appear on a line by itself within
<raw>, as otherwise fast-import will think the data ends
earlier than it really does. The LF immediately trailing
<raw> is part of <raw>. This is one of the limitations
of the delimited format, it is impossible to supply a
data chunk which does not have an LF as its last byte.
The LF after <delim> LF is optional (it used to be
required).
checkpoint
Forces fast-import to close the current packfile, start a
new one, and to save out all current branch refs, tags and
marks.
'checkpoint' LF
LF?
Note that fast-import automatically switches packfiles when
the current packfile reaches --max-pack-size, or 4 GiB,
whichever limit is smaller. During an automatic packfile
switch fast-import does not update the branch refs, tags or
marks.
As a checkpoint can require a significant amount of CPU time
and disk IO (to compute the overall pack SHA-1 checksum,
generate the corresponding index file, and update the refs)
it can easily take several minutes for a single checkpoint
command to complete.
Frontends may choose to issue checkpoints during extremely
large and long running imports, or when they need to allow
another Git process access to a branch. However given that a
30 GiB Subversion repository can be loaded into Git through
fast-import in about 3 hours, explicit checkpointing may not
be necessary.
The LF after the command is optional (it used to be
required).
progress
Causes fast-import to print the entire progress line
unmodified to its standard output channel (file descriptor
1) when the command is processed from the input stream. The
command otherwise has no impact on the current import, or on
any of fast-import's internal state.
'progress' SP <any> LF
LF?
Git 1.7.9.2 Last change: 02/22/2012 18
Git Manual GIT-FAST-IMPORT(1)
The <any> part of the command may contain any sequence of
bytes that does not contain LF. The LF after the command is
optional. Callers may wish to process the output through a
tool such as sed to remove the leading part of the line, for
example:
frontend | git fast-import | sed 's/^progress //'
Placing a progress command immediately after a checkpoint
will inform the reader when the checkpoint has been
completed and it can safely access the refs that fast-import
updated.
cat-blob
Causes fast-import to print a blob to a file descriptor
previously arranged with the --cat-blob-fd argument. The
command otherwise has no impact on the current import; its
main purpose is to retrieve blobs that may be in
fast-import's memory but not accessible from the target
repository.
'cat-blob' SP <dataref> LF
The <dataref> can be either a mark reference (:<idnum>) set
previously or a full 40-byte SHA-1 of a Git blob,
preexisting or ready to be written.
Output uses the same format as git cat-file --batch:
<sha1> SP 'blob' SP <size> LF
<contents> LF
This command can be used anywhere in the stream that
comments are accepted. In particular, the cat-blob command
can be used in the middle of a commit but not in the middle
of a data command.
ls
Prints information about the object at a path to a file
descriptor previously arranged with the --cat-blob-fd
argument. This allows printing a blob from the active commit
(with cat-blob) or copying a blob or tree from a previous
commit for use in the current one (with filemodify).
The ls command can be used anywhere in the stream that
comments are accepted, including the middle of a commit.
Reading from the active commit
This form can only be used in the middle of a commit.
The path names a directory entry within fast-import's
active commit. The path must be quoted in this case.
Git 1.7.9.2 Last change: 02/22/2012 19
Git Manual GIT-FAST-IMPORT(1)
'ls' SP <path> LF
Reading from a named tree
The <dataref> can be a mark reference (:<idnum>) or the
full 40-byte SHA-1 of a Git tag, commit, or tree object,
preexisting or waiting to be written. The path is
relative to the top level of the tree named by
<dataref>.
'ls' SP <dataref> SP <path> LF
See filemodify above for a detailed description of <path>.
Output uses the same format as git ls-tree <tree> -- <path>:
<mode> SP ('blob' | 'tree' | 'commit') SP <dataref> HT <path> LF
The <dataref> represents the blob, tree, or commit object at
<path> and can be used in later cat-blob, filemodify, or ls
commands.
If there is no file or subtree at that path, git fast-import
will instead report
missing SP <path> LF
feature
Require that fast-import supports the specified feature, or
abort if it does not.
'feature' SP <feature> ('=' <argument>)? LF
The <feature> part of the command may be any one of the
following:
date-format, export-marks, relative-marks,
no-relative-marks, force
Act as though the corresponding command-line option with
a leading -- was passed on the command line (see
OPTIONS, above).
import-marks, 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.
Git 1.7.9.2 Last change: 02/22/2012 20
Git Manual GIT-FAST-IMPORT(1)
cat-blob, ls
Require that the backend support the cat-blob or ls
command. Versions of fast-import not supporting the
specified command will exit with a message indicating
so. This lets the import error out early with a clear
message, rather than wasting time on the early part of
an import before the unsupported command is detected.
notes
Require that the backend support the notemodify (N)
subcommand to the commit command. Versions of
fast-import not supporting notes will exit with a
message indicating so.
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.
option
Processes the specified option so that git fast-import
behaves in a way that suits the frontend's needs. Note that
options specified by the frontend are overridden by any
options the user may specify to git fast-import itself.
'option' SP <option> LF
The <option> part of the command may contain any of the
options listed in the OPTIONS section that do not change
import semantics, without the leading -- and is treated in
the same way.
Option commands must be the first commands on the input (not
counting feature commands), to give an option command after
any non-option command is an error.
The following commandline options change import semantics
and may therefore not be passed as option:
o date-format
o import-marks
o export-marks
o cat-blob-fd
o force
done
If the done feature is not in use, treated as if EOF was
Git 1.7.9.2 Last change: 02/22/2012 21
Git Manual GIT-FAST-IMPORT(1)
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.
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
Git 1.7.9.2 Last change: 02/22/2012 22
Git Manual GIT-FAST-IMPORT(1)
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
Git 1.7.9.2 Last change: 02/22/2012 23
Git Manual GIT-FAST-IMPORT(1)
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.
Git 1.7.9.2 Last change: 02/22/2012 24
Git Manual GIT-FAST-IMPORT(1)
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.
Git 1.7.9.2 Last change: 02/22/2012 25
Git Manual GIT-FAST-IMPORT(1)
The packfile(s) created by fast-import do not encourage good
disk access patterns. This is caused by fast-import writing
the data in the order it is received on standard input,
while Git typically organizes data within packfiles to make
the most recent (current tip) data appear before historical
data. Git also clusters commits together, speeding up
revision traversal through better cache locality.
For this reason it is strongly recommended that users repack
the repository with git repack -a -d after fast-import
completes, allowing Git to reorganize the packfiles for
faster data access. If blob deltas are suboptimal (see
above) then also adding the -f option to force recomputation
of all deltas can significantly reduce the final packfile
size (30-50% smaller can be quite typical).
MEMORY UTILIZATION
There are a number of factors which affect how much memory
fast-import requires to perform an import. Like critical
sections of core Git, fast-import uses its own memory
allocators to amortize any overheads associated with malloc.
In practice fast-import tends to amortize any malloc
overheads to 0, due to its use of large block allocations.
per object
fast-import maintains an in-memory structure for every
object written in this execution. On a 32 bit system the
structure is 32 bytes, on a 64 bit system the structure is
40 bytes (due to the larger pointer sizes). Objects in the
table are not deallocated until fast-import terminates.
Importing 2 million objects on a 32 bit system will require
approximately 64 MiB of memory.
The object table is actually a hashtable keyed on the object
name (the unique SHA-1). This storage configuration allows
fast-import to reuse an existing or already written object
and avoid writing duplicates to the output packfile.
Duplicate blobs are surprisingly common in an import,
typically due to branch merges in the source.
per mark
Marks are stored in a sparse array, using 1 pointer (4 bytes
or 8 bytes, depending on pointer size) per mark. Although
the array is sparse, frontends are still strongly encouraged
to use marks between 1 and n, where n is the total number of
marks required for this import.
per branch
Branches are classified as active and inactive. The memory
usage of the two classes is significantly different.
Inactive branches are stored in a structure which uses 96 or
Git 1.7.9.2 Last change: 02/22/2012 26
Git Manual GIT-FAST-IMPORT(1)
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.
GIT
Part of the git(1) suite
Git 1.7.9.2 Last change: 02/22/2012 27
Git Manual GIT-FAST-IMPORT(1)
ATTRIBUTES
See attributes(5) for descriptions of the following
attributes:
+---------------+--------------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+--------------------------+
|Availability | developer/versioning/git |
+---------------+--------------------------+
|Stability | Uncommitted |
+---------------+--------------------------+
NOTES
1. cm@example.com
mailto:cm@example.com
This software was built from source available at
https://java.net/projects/solaris-userland. The original
community source was downloaded from http://git-
core.googlecode.com/files/git-1.7.9.2.tar.gz
Further information about this software can be found on the
open source community website at http://git-scm.com/.
Git 1.7.9.2 Last change: 02/22/2012 28