config: display key_delim for config --bool --get-regexp
[git/git.git] / Documentation / git-fast-import.txt
1 git-fast-import(1)
2 ==================
5 ----
6 git-fast-import - Backend for fast Git data importers
10 --------
11 frontend | 'git fast-import' [options]
14 -----------
15 This program is usually not what the end user wants to run directly.
16 Most end users want to use one of the existing frontend programs,
17 which parses a specific type of foreign source and feeds the contents
18 stored there to 'git fast-import'.
20 fast-import reads a mixed command/data stream from standard input and
21 writes one or more packfiles directly into the current repository.
22 When EOF is received on standard input, fast import writes out
23 updated branch and tag refs, fully updating the current repository
24 with the newly imported data.
26 The fast-import backend itself can import into an empty repository (one that
27 has already been initialized by 'git init') or incrementally
28 update an existing populated repository. Whether or not incremental
29 imports are supported from a particular foreign source depends on
30 the frontend program in use.
34 -------
35 --date-format=<fmt>::
36 Specify the type of dates the frontend will supply to
37 fast-import within `author`, `committer` and `tagger` commands.
38 See ``Date Formats'' below for details about which formats
39 are supported, and their syntax.
41 --force::
42 Force updating modified existing branches, even if doing
43 so would cause commits to be lost (as the new commit does
44 not contain the old commit).
46 --max-pack-size=<n>::
47 Maximum size of each output packfile.
48 The default is unlimited.
50 --big-file-threshold=<n>::
51 Maximum size of a blob that fast-import will attempt to
52 create a delta for, expressed in bytes. The default is 512m
53 (512 MiB). Some importers may wish to lower this on systems
54 with constrained memory.
56 --depth=<n>::
57 Maximum delta depth, for blob and tree deltification.
58 Default is 10.
60 --active-branches=<n>::
61 Maximum number of branches to maintain active at once.
62 See ``Memory Utilization'' below for details. Default is 5.
64 --export-marks=<file>::
65 Dumps the internal marks table to <file> when complete.
66 Marks are written one per line as `:markid SHA-1`.
67 Frontends can use this file to validate imports after they
68 have been completed, or to save the marks table across
69 incremental runs. As <file> is only opened and truncated
70 at checkpoint (or completion) the same path can also be
71 safely given to \--import-marks.
73 --import-marks=<file>::
74 Before processing any input, load the marks specified in
75 <file>. The input file must exist, must be readable, and
76 must use the same format as produced by \--export-marks.
77 Multiple options may be supplied to import more than one
78 set of marks. If a mark is defined to different values,
79 the last file wins.
81 --relative-marks::
82 After specifying --relative-marks= the paths specified
83 with --import-marks= and --export-marks= are relative
84 to an internal directory in the current repository.
85 In git-fast-import this means that the paths are relative
86 to the .git/info/fast-import directory. However, other
87 importers may use a different location.
89 --no-relative-marks::
90 Negates a previous --relative-marks. Allows for combining
91 relative and non-relative marks by interweaving
92 --(no-)-relative-marks= with the --(import|export)-marks=
93 options.
95 --cat-blob-fd=<fd>::
96 Specify the file descriptor that will be written to
97 when the `cat-blob` command is encountered in the stream.
98 The default behaviour is to write to `stdout`.
100 --export-pack-edges=<file>::
101 After creating a packfile, print a line of data to
102 <file> listing the filename of the packfile and the last
103 commit on each branch that was written to that packfile.
104 This information may be useful after importing projects
105 whose total object set exceeds the 4 GiB packfile limit,
106 as these commits can be used as edge points during calls
107 to 'git pack-objects'.
109 --quiet::
110 Disable all non-fatal output, making fast-import silent when it
111 is successful. This option disables the output shown by
112 \--stats.
114 --stats::
115 Display some basic statistics about the objects fast-import has
116 created, the packfiles they were stored into, and the
117 memory used by fast-import during this run. Showing this output
118 is currently the default, but can be disabled with \--quiet.
121 Performance
122 -----------
123 The design of fast-import allows it to import large projects in a minimum
124 amount of memory usage and processing time. Assuming the frontend
125 is able to keep up with fast-import and feed it a constant stream of data,
126 import times for projects holding 10+ years of history and containing
127 100,000+ individual commits are generally completed in just 1-2
128 hours on quite modest (~$2,000 USD) hardware.
130 Most bottlenecks appear to be in foreign source data access (the
131 source just cannot extract revisions fast enough) or disk IO (fast-import
132 writes as fast as the disk will take the data). Imports will run
133 faster if the source data is stored on a different drive than the
134 destination Git repository (due to less IO contention).
137 Development Cost
138 ----------------
139 A typical frontend for fast-import tends to weigh in at approximately 200
140 lines of Perl/Python/Ruby code. Most developers have been able to
141 create working importers in just a couple of hours, even though it
142 is their first exposure to fast-import, and sometimes even to Git. This is
143 an ideal situation, given that most conversion tools are throw-away
144 (use once, and never look back).
147 Parallel Operation
148 ------------------
149 Like 'git push' or 'git fetch', imports handled by fast-import are safe to
150 run alongside parallel `git repack -a -d` or `git gc` invocations,
151 or any other Git operation (including 'git prune', as loose objects
152 are never used by fast-import).
154 fast-import does not lock the branch or tag refs it is actively importing.
155 After the import, during its ref update phase, fast-import tests each
156 existing branch ref to verify the update will be a fast-forward
157 update (the commit stored in the ref is contained in the new
158 history of the commit to be written). If the update is not a
159 fast-forward update, fast-import will skip updating that ref and instead
160 prints a warning message. fast-import will always attempt to update all
161 branch refs, and does not stop on the first failure.
163 Branch updates can be forced with \--force, but it's recommended that
164 this only be used on an otherwise quiet repository. Using \--force
165 is not necessary for an initial import into an empty repository.
168 Technical Discussion
169 --------------------
170 fast-import tracks a set of branches in memory. Any branch can be created
171 or modified at any point during the import process by sending a
172 `commit` command on the input stream. This design allows a frontend
173 program to process an unlimited number of branches simultaneously,
174 generating commits in the order they are available from the source
175 data. It also simplifies the frontend programs considerably.
177 fast-import does not use or alter the current working directory, or any
178 file within it. (It does however update the current Git repository,
179 as referenced by `GIT_DIR`.) Therefore an import frontend may use
180 the working directory for its own purposes, such as extracting file
181 revisions from the foreign source. This ignorance of the working
182 directory also allows fast-import to run very quickly, as it does not
183 need to perform any costly file update operations when switching
184 between branches.
186 Input Format
187 ------------
188 With the exception of raw file data (which Git does not interpret)
189 the fast-import input format is text (ASCII) based. This text based
190 format simplifies development and debugging of frontend programs,
191 especially when a higher level language such as Perl, Python or
192 Ruby is being used.
194 fast-import is very strict about its input. Where we say SP below we mean
195 *exactly* one space. Likewise LF means one (and only one) linefeed.
196 Supplying additional whitespace characters will cause unexpected
197 results, such as branch names or file names with leading or trailing
198 spaces in their name, or early termination of fast-import when it encounters
199 unexpected input.
201 Stream Comments
202 ~~~~~~~~~~~~~~~
203 To aid in debugging frontends fast-import ignores any line that
204 begins with `#` (ASCII pound/hash) up to and including the line
205 ending `LF`. A comment line may contain any sequence of bytes
206 that does not contain an LF and therefore may be used to include
207 any detailed debugging information that might be specific to the
208 frontend and useful when inspecting a fast-import data stream.
210 Date Formats
211 ~~~~~~~~~~~~
212 The following date formats are supported. A frontend should select
213 the format it will use for this import by passing the format name
214 in the \--date-format=<fmt> command line option.
216 `raw`::
217 This is the Git native format and is `<time> SP <offutc>`.
218 It is also fast-import's default format, if \--date-format was
219 not specified.
220 +
221 The time of the event is specified by `<time>` as the number of
222 seconds since the UNIX epoch (midnight, Jan 1, 1970, UTC) and is
223 written as an ASCII decimal integer.
224 +
225 The local offset is specified by `<offutc>` as a positive or negative
226 offset from UTC. For example EST (which is 5 hours behind UTC)
227 would be expressed in `<tz>` by ``-0500'' while UTC is ``+0000''.
228 The local offset does not affect `<time>`; it is used only as an
229 advisement to help formatting routines display the timestamp.
230 +
231 If the local offset is not available in the source material, use
232 ``+0000'', or the most common local offset. For example many
233 organizations have a CVS repository which has only ever been accessed
234 by users who are located in the same location and timezone. In this
235 case a reasonable offset from UTC could be assumed.
236 +
237 Unlike the `rfc2822` format, this format is very strict. Any
238 variation in formatting will cause fast-import to reject the value.
240 `rfc2822`::
241 This is the standard email format as described by RFC 2822.
242 +
243 An example value is ``Tue Feb 6 11:22:18 2007 -0500''. The Git
244 parser is accurate, but a little on the lenient side. It is the
245 same parser used by 'git am' when applying patches
246 received from email.
247 +
248 Some malformed strings may be accepted as valid dates. In some of
249 these cases Git will still be able to obtain the correct date from
250 the malformed string. There are also some types of malformed
251 strings which Git will parse wrong, and yet consider valid.
252 Seriously malformed strings will be rejected.
253 +
254 Unlike the `raw` format above, the timezone/UTC offset information
255 contained in an RFC 2822 date string is used to adjust the date
256 value to UTC prior to storage. Therefore it is important that
257 this information be as accurate as possible.
258 +
259 If the source material uses RFC 2822 style dates,
260 the frontend should let fast-import handle the parsing and conversion
261 (rather than attempting to do it itself) as the Git parser has
262 been well tested in the wild.
263 +
264 Frontends should prefer the `raw` format if the source material
265 already uses UNIX-epoch format, can be coaxed to give dates in that
266 format, or its format is easily convertible to it, as there is no
267 ambiguity in parsing.
269 `now`::
270 Always use the current time and timezone. The literal
271 `now` must always be supplied for `<when>`.
272 +
273 This is a toy format. The current time and timezone of this system
274 is always copied into the identity string at the time it is being
275 created by fast-import. There is no way to specify a different time or
276 timezone.
277 +
278 This particular format is supplied as it's short to implement and
279 may be useful to a process that wants to create a new commit
280 right now, without needing to use a working directory or
281 'git update-index'.
282 +
283 If separate `author` and `committer` commands are used in a `commit`
284 the timestamps may not match, as the system clock will be polled
285 twice (once for each command). The only way to ensure that both
286 author and committer identity information has the same timestamp
287 is to omit `author` (thus copying from `committer`) or to use a
288 date format other than `now`.
290 Commands
291 ~~~~~~~~
292 fast-import accepts several commands to update the current repository
293 and control the current import process. More detailed discussion
294 (with examples) of each command follows later.
296 `commit`::
297 Creates a new branch or updates an existing branch by
298 creating a new commit and updating the branch to point at
299 the newly created commit.
301 `tag`::
302 Creates an annotated tag object from an existing commit or
303 branch. Lightweight tags are not supported by this command,
304 as they are not recommended for recording meaningful points
305 in time.
307 `reset`::
308 Reset an existing branch (or a new branch) to a specific
309 revision. This command must be used to change a branch to
310 a specific revision without making a commit on it.
312 `blob`::
313 Convert raw file data into a blob, for future use in a
314 `commit` command. This command is optional and is not
315 needed to perform an import.
317 `checkpoint`::
318 Forces fast-import to close the current packfile, generate its
319 unique SHA-1 checksum and index, and start a new packfile.
320 This command is optional and is not needed to perform
321 an import.
323 `progress`::
324 Causes fast-import to echo the entire line to its own
325 standard output. This command is optional and is not needed
326 to perform an import.
328 `cat-blob`::
329 Causes fast-import to print a blob in 'cat-file --batch'
330 format to the file descriptor set with `--cat-blob-fd` or
331 `stdout` if unspecified.
333 `feature`::
334 Require that fast-import supports the specified feature, or
335 abort if it does not.
337 `option`::
338 Specify any of the options listed under OPTIONS that do not
339 change stream semantic to suit the frontend's needs. This
340 command is optional and is not needed to perform an import.
342 `commit`
343 ~~~~~~~~
344 Create or update a branch with a new commit, recording one logical
345 change to the project.
347 ....
348 'commit' SP <ref> LF
349 mark?
350 ('author' (SP <name>)? SP LT <email> GT SP <when> LF)?
351 'committer' (SP <name>)? SP LT <email> GT SP <when> LF
352 data
353 ('from' SP <committish> LF)?
354 ('merge' SP <committish> LF)?
355 (filemodify | filedelete | filecopy | filerename | filedeleteall | notemodify)*
356 LF?
357 ....
359 where `<ref>` is the name of the branch to make the commit on.
360 Typically branch names are prefixed with `refs/heads/` in
361 Git, so importing the CVS branch symbol `RELENG-1_0` would use
362 `refs/heads/RELENG-1_0` for the value of `<ref>`. The value of
363 `<ref>` must be a valid refname in Git. As `LF` is not valid in
364 a Git refname, no quoting or escaping syntax is supported here.
366 A `mark` command may optionally appear, requesting fast-import to save a
367 reference to the newly created commit for future use by the frontend
368 (see below for format). It is very common for frontends to mark
369 every commit they create, thereby allowing future branch creation
370 from any imported commit.
372 The `data` command following `committer` must supply the commit
373 message (see below for `data` command syntax). To import an empty
374 commit message use a 0 length data. Commit messages are free-form
375 and are not interpreted by Git. Currently they must be encoded in
376 UTF-8, as fast-import does not permit other encodings to be specified.
378 Zero or more `filemodify`, `filedelete`, `filecopy`, `filerename`,
379 `filedeleteall` and `notemodify` commands
380 may be included to update the contents of the branch prior to
381 creating the commit. These commands may be supplied in any order.
382 However it is recommended that a `filedeleteall` command precede
383 all `filemodify`, `filecopy`, `filerename` and `notemodify` commands in
384 the same commit, as `filedeleteall` wipes the branch clean (see below).
386 The `LF` after the command is optional (it used to be required).
388 `author`
389 ^^^^^^^^
390 An `author` command may optionally appear, if the author information
391 might differ from the committer information. If `author` is omitted
392 then fast-import will automatically use the committer's information for
393 the author portion of the commit. See below for a description of
394 the fields in `author`, as they are identical to `committer`.
396 `committer`
397 ^^^^^^^^^^^
398 The `committer` command indicates who made this commit, and when
399 they made it.
401 Here `<name>` is the person's display name (for example
402 ``Com M Itter'') and `<email>` is the person's email address
403 (``''). `LT` and `GT` are the literal less-than (\x3c)
404 and greater-than (\x3e) symbols. These are required to delimit
405 the email address from the other fields in the line. Note that
406 `<name>` is free-form and may contain any sequence of bytes, except
407 `LT` and `LF`. It is typically UTF-8 encoded.
409 The time of the change is specified by `<when>` using the date format
410 that was selected by the \--date-format=<fmt> command line option.
411 See ``Date Formats'' above for the set of supported formats, and
412 their syntax.
414 `from`
415 ^^^^^^
416 The `from` command is used to specify the commit to initialize
417 this branch from. This revision will be the first ancestor of the
418 new commit.
420 Omitting the `from` command in the first commit of a new branch
421 will cause fast-import to create that commit with no ancestor. This
422 tends to be desired only for the initial commit of a project.
423 If the frontend creates all files from scratch when making a new
424 branch, a `merge` command may be used instead of `from` to start
425 the commit with an empty tree.
426 Omitting the `from` command on existing branches is usually desired,
427 as the current commit on that branch is automatically assumed to
428 be the first ancestor of the new commit.
430 As `LF` is not valid in a Git refname or SHA-1 expression, no
431 quoting or escaping syntax is supported within `<committish>`.
433 Here `<committish>` is any of the following:
435 * The name of an existing branch already in fast-import's internal branch
436 table. If fast-import doesn't know the name, it's treated as a SHA-1
437 expression.
439 * A mark reference, `:<idnum>`, where `<idnum>` is the mark number.
440 +
441 The reason fast-import uses `:` to denote a mark reference is this character
442 is not legal in a Git branch name. The leading `:` makes it easy
443 to distinguish between the mark 42 (`:42`) and the branch 42 (`42`
444 or `refs/heads/42`), or an abbreviated SHA-1 which happened to
445 consist only of base-10 digits.
446 +
447 Marks must be declared (via `mark`) before they can be used.
449 * A complete 40 byte or abbreviated commit SHA-1 in hex.
451 * Any valid Git SHA-1 expression that resolves to a commit. See
452 ``SPECIFYING REVISIONS'' in linkgit:gitrevisions[7] for details.
454 The special case of restarting an incremental import from the
455 current branch value should be written as:
456 ----
457 from refs/heads/branch^0
458 ----
459 The `{caret}0` suffix is necessary as fast-import does not permit a branch to
460 start from itself, and the branch is created in memory before the
461 `from` command is even read from the input. Adding `{caret}0` will force
462 fast-import to resolve the commit through Git's revision parsing library,
463 rather than its internal branch table, thereby loading in the
464 existing value of the branch.
466 `merge`
467 ^^^^^^^
468 Includes one additional ancestor commit. If the `from` command is
469 omitted when creating a new branch, the first `merge` commit will be
470 the first ancestor of the current commit, and the branch will start
471 out with no files. An unlimited number of `merge` commands per
472 commit are permitted by fast-import, thereby establishing an n-way merge.
473 However Git's other tools never create commits with more than 15
474 additional ancestors (forming a 16-way merge). For this reason
475 it is suggested that frontends do not use more than 15 `merge`
476 commands per commit; 16, if starting a new, empty branch.
478 Here `<committish>` is any of the commit specification expressions
479 also accepted by `from` (see above).
481 `filemodify`
482 ^^^^^^^^^^^^
483 Included in a `commit` command to add a new file or change the
484 content of an existing file. This command has two different means
485 of specifying the content of the file.
487 External data format::
488 The data content for the file was already supplied by a prior
489 `blob` command. The frontend just needs to connect it.
490 +
491 ....
492 'M' SP <mode> SP <dataref> SP <path> LF
493 ....
494 +
495 Here usually `<dataref>` must be either a mark reference (`:<idnum>`)
496 set by a prior `blob` command, or a full 40-byte SHA-1 of an
497 existing Git blob object. If `<mode>` is `040000`` then
498 `<dataref>` must be the full 40-byte SHA-1 of an existing
499 Git tree object or a mark reference set with `--import-marks`.
501 Inline data format::
502 The data content for the file has not been supplied yet.
503 The frontend wants to supply it as part of this modify
504 command.
505 +
506 ....
507 'M' SP <mode> SP 'inline' SP <path> LF
508 data
509 ....
510 +
511 See below for a detailed description of the `data` command.
513 In both formats `<mode>` is the type of file entry, specified
514 in octal. Git only supports the following modes:
516 * `100644` or `644`: A normal (not-executable) file. The majority
517 of files in most projects use this mode. If in doubt, this is
518 what you want.
519 * `100755` or `755`: A normal, but executable, file.
520 * `120000`: A symlink, the content of the file will be the link target.
521 * `160000`: A gitlink, SHA-1 of the object refers to a commit in
522 another repository. Git links can only be specified by SHA or through
523 a commit mark. They are used to implement submodules.
524 * `040000`: A subdirectory. Subdirectories can only be specified by
525 SHA or through a tree mark set with `--import-marks`.
527 In both formats `<path>` is the complete path of the file to be added
528 (if not already existing) or modified (if already existing).
530 A `<path>` string must use UNIX-style directory separators (forward
531 slash `/`), may contain any byte other than `LF`, and must not
532 start with double quote (`"`).
534 If an `LF` or double quote must be encoded into `<path>` shell-style
535 quoting should be used, e.g. `"path/with\n and \" in it"`.
537 The value of `<path>` must be in canonical form. That is it must not:
539 * contain an empty directory component (e.g. `foo//bar` is invalid),
540 * end with a directory separator (e.g. `foo/` is invalid),
541 * start with a directory separator (e.g. `/foo` is invalid),
542 * contain the special component `.` or `..` (e.g. `foo/./bar` and
543 `foo/../bar` are invalid).
545 The root of the tree can be represented by an empty string as `<path>`.
547 It is recommended that `<path>` always be encoded using UTF-8.
549 `filedelete`
550 ^^^^^^^^^^^^
551 Included in a `commit` command to remove a file or recursively
552 delete an entire directory from the branch. If the file or directory
553 removal makes its parent directory empty, the parent directory will
554 be automatically removed too. This cascades up the tree until the
555 first non-empty directory or the root is reached.
557 ....
558 'D' SP <path> LF
559 ....
561 here `<path>` is the complete path of the file or subdirectory to
562 be removed from the branch.
563 See `filemodify` above for a detailed description of `<path>`.
565 `filecopy`
566 ^^^^^^^^^^^^
567 Recursively copies an existing file or subdirectory to a different
568 location within the branch. The existing file or directory must
569 exist. If the destination exists it will be completely replaced
570 by the content copied from the source.
572 ....
573 'C' SP <path> SP <path> LF
574 ....
576 here the first `<path>` is the source location and the second
577 `<path>` is the destination. See `filemodify` above for a detailed
578 description of what `<path>` may look like. To use a source path
579 that contains SP the path must be quoted.
581 A `filecopy` command takes effect immediately. Once the source
582 location has been copied to the destination any future commands
583 applied to the source location will not impact the destination of
584 the copy.
586 `filerename`
587 ^^^^^^^^^^^^
588 Renames an existing file or subdirectory to a different location
589 within the branch. The existing file or directory must exist. If
590 the destination exists it will be replaced by the source directory.
592 ....
593 'R' SP <path> SP <path> LF
594 ....
596 here the first `<path>` is the source location and the second
597 `<path>` is the destination. See `filemodify` above for a detailed
598 description of what `<path>` may look like. To use a source path
599 that contains SP the path must be quoted.
601 A `filerename` command takes effect immediately. Once the source
602 location has been renamed to the destination any future commands
603 applied to the source location will create new files there and not
604 impact the destination of the rename.
606 Note that a `filerename` is the same as a `filecopy` followed by a
607 `filedelete` of the source location. There is a slight performance
608 advantage to using `filerename`, but the advantage is so small
609 that it is never worth trying to convert a delete/add pair in
610 source material into a rename for fast-import. This `filerename`
611 command is provided just to simplify frontends that already have
612 rename information and don't want bother with decomposing it into a
613 `filecopy` followed by a `filedelete`.
615 `filedeleteall`
616 ^^^^^^^^^^^^^^^
617 Included in a `commit` command to remove all files (and also all
618 directories) from the branch. This command resets the internal
619 branch structure to have no files in it, allowing the frontend
620 to subsequently add all interesting files from scratch.
622 ....
623 'deleteall' LF
624 ....
626 This command is extremely useful if the frontend does not know
627 (or does not care to know) what files are currently on the branch,
628 and therefore cannot generate the proper `filedelete` commands to
629 update the content.
631 Issuing a `filedeleteall` followed by the needed `filemodify`
632 commands to set the correct content will produce the same results
633 as sending only the needed `filemodify` and `filedelete` commands.
634 The `filedeleteall` approach may however require fast-import to use slightly
635 more memory per active branch (less than 1 MiB for even most large
636 projects); so frontends that can easily obtain only the affected
637 paths for a commit are encouraged to do so.
639 `notemodify`
640 ^^^^^^^^^^^^
641 Included in a `commit` command to add a new note (annotating a given
642 commit) or change the content of an existing note. This command has
643 two different means of specifying the content of the note.
645 External data format::
646 The data content for the note was already supplied by a prior
647 `blob` command. The frontend just needs to connect it to the
648 commit that is to be annotated.
649 +
650 ....
651 'N' SP <dataref> SP <committish> LF
652 ....
653 +
654 Here `<dataref>` can be either a mark reference (`:<idnum>`)
655 set by a prior `blob` command, or a full 40-byte SHA-1 of an
656 existing Git blob object.
658 Inline data format::
659 The data content for the note has not been supplied yet.
660 The frontend wants to supply it as part of this modify
661 command.
662 +
663 ....
664 'N' SP 'inline' SP <committish> LF
665 data
666 ....
667 +
668 See below for a detailed description of the `data` command.
670 In both formats `<committish>` is any of the commit specification
671 expressions also accepted by `from` (see above).
673 `mark`
674 ~~~~~~
675 Arranges for fast-import to save a reference to the current object, allowing
676 the frontend to recall this object at a future point in time, without
677 knowing its SHA-1. Here the current object is the object creation
678 command the `mark` command appears within. This can be `commit`,
679 `tag`, and `blob`, but `commit` is the most common usage.
681 ....
682 'mark' SP ':' <idnum> LF
683 ....
685 where `<idnum>` is the number assigned by the frontend to this mark.
686 The value of `<idnum>` is expressed as an ASCII decimal integer.
687 The value 0 is reserved and cannot be used as
688 a mark. Only values greater than or equal to 1 may be used as marks.
690 New marks are created automatically. Existing marks can be moved
691 to another object simply by reusing the same `<idnum>` in another
692 `mark` command.
694 `tag`
695 ~~~~~
696 Creates an annotated tag referring to a specific commit. To create
697 lightweight (non-annotated) tags see the `reset` command below.
699 ....
700 'tag' SP <name> LF
701 'from' SP <committish> LF
702 'tagger' (SP <name>)? SP LT <email> GT SP <when> LF
703 data
704 ....
706 where `<name>` is the name of the tag to create.
708 Tag names are automatically prefixed with `refs/tags/` when stored
709 in Git, so importing the CVS branch symbol `RELENG-1_0-FINAL` would
710 use just `RELENG-1_0-FINAL` for `<name>`, and fast-import will write the
711 corresponding ref as `refs/tags/RELENG-1_0-FINAL`.
713 The value of `<name>` must be a valid refname in Git and therefore
714 may contain forward slashes. As `LF` is not valid in a Git refname,
715 no quoting or escaping syntax is supported here.
717 The `from` command is the same as in the `commit` command; see
718 above for details.
720 The `tagger` command uses the same format as `committer` within
721 `commit`; again see above for details.
723 The `data` command following `tagger` must supply the annotated tag
724 message (see below for `data` command syntax). To import an empty
725 tag message use a 0 length data. Tag messages are free-form and are
726 not interpreted by Git. Currently they must be encoded in UTF-8,
727 as fast-import does not permit other encodings to be specified.
729 Signing annotated tags during import from within fast-import is not
730 supported. Trying to include your own PGP/GPG signature is not
731 recommended, as the frontend does not (easily) have access to the
732 complete set of bytes which normally goes into such a signature.
733 If signing is required, create lightweight tags from within fast-import with
734 `reset`, then create the annotated versions of those tags offline
735 with the standard 'git tag' process.
737 `reset`
738 ~~~~~~~
739 Creates (or recreates) the named branch, optionally starting from
740 a specific revision. The reset command allows a frontend to issue
741 a new `from` command for an existing branch, or to create a new
742 branch from an existing commit without creating a new commit.
744 ....
745 'reset' SP <ref> LF
746 ('from' SP <committish> LF)?
747 LF?
748 ....
750 For a detailed description of `<ref>` and `<committish>` see above
751 under `commit` and `from`.
753 The `LF` after the command is optional (it used to be required).
755 The `reset` command can also be used to create lightweight
756 (non-annotated) tags. For example:
758 ====
759 reset refs/tags/938
760 from :938
761 ====
763 would create the lightweight tag `refs/tags/938` referring to
764 whatever commit mark `:938` references.
766 `blob`
767 ~~~~~~
768 Requests writing one file revision to the packfile. The revision
769 is not connected to any commit; this connection must be formed in
770 a subsequent `commit` command by referencing the blob through an
771 assigned mark.
773 ....
774 'blob' LF
775 mark?
776 data
777 ....
779 The mark command is optional here as some frontends have chosen
780 to generate the Git SHA-1 for the blob on their own, and feed that
781 directly to `commit`. This is typically more work than it's worth
782 however, as marks are inexpensive to store and easy to use.
784 `data`
785 ~~~~~~
786 Supplies raw data (for use as blob/file content, commit messages, or
787 annotated tag messages) to fast-import. Data can be supplied using an exact
788 byte count or delimited with a terminating line. Real frontends
789 intended for production-quality conversions should always use the
790 exact byte count format, as it is more robust and performs better.
791 The delimited format is intended primarily for testing fast-import.
793 Comment lines appearing within the `<raw>` part of `data` commands
794 are always taken to be part of the body of the data and are therefore
795 never ignored by fast-import. This makes it safe to import any
796 file/message content whose lines might start with `#`.
798 Exact byte count format::
799 The frontend must specify the number of bytes of data.
800 +
801 ....
802 'data' SP <count> LF
803 <raw> LF?
804 ....
805 +
806 where `<count>` is the exact number of bytes appearing within
807 `<raw>`. The value of `<count>` is expressed as an ASCII decimal
808 integer. The `LF` on either side of `<raw>` is not
809 included in `<count>` and will not be included in the imported data.
810 +
811 The `LF` after `<raw>` is optional (it used to be required) but
812 recommended. Always including it makes debugging a fast-import
813 stream easier as the next command always starts in column 0
814 of the next line, even if `<raw>` did not end with an `LF`.
816 Delimited format::
817 A delimiter string is used to mark the end of the data.
818 fast-import will compute the length by searching for the delimiter.
819 This format is primarily useful for testing and is not
820 recommended for real data.
821 +
822 ....
823 'data' SP '<<' <delim> LF
824 <raw> LF
825 <delim> LF
826 LF?
827 ....
828 +
829 where `<delim>` is the chosen delimiter string. The string `<delim>`
830 must not appear on a line by itself within `<raw>`, as otherwise
831 fast-import will think the data ends earlier than it really does. The `LF`
832 immediately trailing `<raw>` is part of `<raw>`. This is one of
833 the limitations of the delimited format, it is impossible to supply
834 a data chunk which does not have an LF as its last byte.
835 +
836 The `LF` after `<delim> LF` is optional (it used to be required).
838 `checkpoint`
839 ~~~~~~~~~~~~
840 Forces fast-import to close the current packfile, start a new one, and to
841 save out all current branch refs, tags and marks.
843 ....
844 'checkpoint' LF
845 LF?
846 ....
848 Note that fast-import automatically switches packfiles when the current
849 packfile reaches \--max-pack-size, or 4 GiB, whichever limit is
850 smaller. During an automatic packfile switch fast-import does not update
851 the branch refs, tags or marks.
853 As a `checkpoint` can require a significant amount of CPU time and
854 disk IO (to compute the overall pack SHA-1 checksum, generate the
855 corresponding index file, and update the refs) it can easily take
856 several minutes for a single `checkpoint` command to complete.
858 Frontends may choose to issue checkpoints during extremely large
859 and long running imports, or when they need to allow another Git
860 process access to a branch. However given that a 30 GiB Subversion
861 repository can be loaded into Git through fast-import in about 3 hours,
862 explicit checkpointing may not be necessary.
864 The `LF` after the command is optional (it used to be required).
866 `progress`
867 ~~~~~~~~~~
868 Causes fast-import to print the entire `progress` line unmodified to
869 its standard output channel (file descriptor 1) when the command is
870 processed from the input stream. The command otherwise has no impact
871 on the current import, or on any of fast-import's internal state.
873 ....
874 'progress' SP <any> LF
875 LF?
876 ....
878 The `<any>` part of the command may contain any sequence of bytes
879 that does not contain `LF`. The `LF` after the command is optional.
880 Callers may wish to process the output through a tool such as sed to
881 remove the leading part of the line, for example:
883 ====
884 frontend | git fast-import | sed 's/^progress //'
885 ====
887 Placing a `progress` command immediately after a `checkpoint` will
888 inform the reader when the `checkpoint` has been completed and it
889 can safely access the refs that fast-import updated.
891 `cat-blob`
892 ~~~~~~~~~~
893 Causes fast-import to print a blob to a file descriptor previously
894 arranged with the `--cat-blob-fd` argument. The command otherwise
895 has no impact on the current import; its main purpose is to
896 retrieve blobs that may be in fast-import's memory but not
897 accessible from the target repository.
899 ....
900 'cat-blob' SP <dataref> LF
901 ....
903 The `<dataref>` can be either a mark reference (`:<idnum>`)
904 set previously or a full 40-byte SHA-1 of a Git blob, preexisting or
905 ready to be written.
907 Output uses the same format as `git cat-file --batch`:
909 ====
910 <sha1> SP 'blob' SP <size> LF
911 <contents> LF
912 ====
914 This command can be used anywhere in the stream that comments are
915 accepted. In particular, the `cat-blob` command can be used in the
916 middle of a commit but not in the middle of a `data` command.
918 `feature`
919 ~~~~~~~~~
920 Require that fast-import supports the specified feature, or abort if
921 it does not.
923 ....
924 'feature' SP <feature> ('=' <argument>)? LF
925 ....
927 The <feature> part of the command may be any one of the following:
929 date-format::
930 export-marks::
931 relative-marks::
932 no-relative-marks::
933 force::
934 Act as though the corresponding command-line option with
935 a leading '--' was passed on the command line
936 (see OPTIONS, above).
938 import-marks::
939 Like --import-marks except in two respects: first, only one
940 "feature import-marks" command is allowed per stream;
941 second, an --import-marks= command-line option overrides
942 any "feature import-marks" command in the stream.
944 cat-blob::
945 Ignored. Versions of fast-import not supporting the
946 "cat-blob" command will exit with a message indicating so.
947 This lets the import error out early with a clear message,
948 rather than wasting time on the early part of an import
949 before the unsupported command is detected.
951 `option`
952 ~~~~~~~~
953 Processes the specified option so that git fast-import behaves in a
954 way that suits the frontend's needs.
955 Note that options specified by the frontend are overridden by any
956 options the user may specify to git fast-import itself.
958 ....
959 'option' SP <option> LF
960 ....
962 The `<option>` part of the command may contain any of the options
963 listed in the OPTIONS section that do not change import semantics,
964 without the leading '--' and is treated in the same way.
966 Option commands must be the first commands on the input (not counting
967 feature commands), to give an option command after any non-option
968 command is an error.
970 The following commandline options change import semantics and may therefore
971 not be passed as option:
973 * date-format
974 * import-marks
975 * export-marks
976 * cat-blob-fd
977 * force
979 Crash Reports
980 -------------
981 If fast-import is supplied invalid input it will terminate with a
982 non-zero exit status and create a crash report in the top level of
983 the Git repository it was importing into. Crash reports contain
984 a snapshot of the internal fast-import state as well as the most
985 recent commands that lead up to the crash.
987 All recent commands (including stream comments, file changes and
988 progress commands) are shown in the command history within the crash
989 report, but raw file data and commit messages are excluded from the
990 crash report. This exclusion saves space within the report file
991 and reduces the amount of buffering that fast-import must perform
992 during execution.
994 After writing a crash report fast-import will close the current
995 packfile and export the marks table. This allows the frontend
996 developer to inspect the repository state and resume the import from
997 the point where it crashed. The modified branches and tags are not
998 updated during a crash, as the import did not complete successfully.
999 Branch and tag information can be found in the crash report and
1000 must be applied manually if the update is needed.
1002 An example crash:
1004 ====
1005 $ cat >in <<END_OF_INPUT
1006 # my very first test commit
1007 commit refs/heads/master
1008 committer Shawn O. Pearce <spearce> 19283 -0400
1009 # who is that guy anyway?
1010 data <<EOF
1011 this is my commit
1012 EOF
1013 M 644 inline .gitignore
1014 data <<EOF
1015 .gitignore
1016 EOF
1017 M 777 inline bob
1020 $ git fast-import <in
1021 fatal: Corrupt mode: M 777 inline bob
1022 fast-import: dumping crash report to .git/fast_import_crash_8434
1024 $ cat .git/fast_import_crash_8434
1025 fast-import crash report:
1026 fast-import process: 8434
1027 parent process : 1391
1028 at Sat Sep 1 00:58:12 2007
1030 fatal: Corrupt mode: M 777 inline bob
1032 Most Recent Commands Before Crash
1033 ---------------------------------
1034 # my very first test commit
1035 commit refs/heads/master
1036 committer Shawn O. Pearce <spearce> 19283 -0400
1037 # who is that guy anyway?
1038 data <<EOF
1039 M 644 inline .gitignore
1040 data <<EOF
1041 * M 777 inline bob
1043 Active Branch LRU
1044 -----------------
1045 active_branches = 1 cur, 5 max
1047 pos clock name
1048 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1049 1) 0 refs/heads/master
1051 Inactive Branches
1052 -----------------
1053 refs/heads/master:
1054 status : active loaded dirty
1055 tip commit : 0000000000000000000000000000000000000000
1056 old tree : 0000000000000000000000000000000000000000
1057 cur tree : 0000000000000000000000000000000000000000
1058 commit clock: 0
1059 last pack :
1062 -------------------
1064 ====
1066 Tips and Tricks
1067 ---------------
1068 The following tips and tricks have been collected from various
1069 users of fast-import, and are offered here as suggestions.
1071 Use One Mark Per Commit
1072 ~~~~~~~~~~~~~~~~~~~~~~~
1073 When doing a repository conversion, use a unique mark per commit
1074 (`mark :<n>`) and supply the \--export-marks option on the command
1075 line. fast-import will dump a file which lists every mark and the Git
1076 object SHA-1 that corresponds to it. If the frontend can tie
1077 the marks back to the source repository, it is easy to verify the
1078 accuracy and completeness of the import by comparing each Git
1079 commit to the corresponding source revision.
1081 Coming from a system such as Perforce or Subversion this should be
1082 quite simple, as the fast-import mark can also be the Perforce changeset
1083 number or the Subversion revision number.
1085 Freely Skip Around Branches
1086 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
1087 Don't bother trying to optimize the frontend to stick to one branch
1088 at a time during an import. Although doing so might be slightly
1089 faster for fast-import, it tends to increase the complexity of the frontend
1090 code considerably.
1092 The branch LRU builtin to fast-import tends to behave very well, and the
1093 cost of activating an inactive branch is so low that bouncing around
1094 between branches has virtually no impact on import performance.
1096 Handling Renames
1097 ~~~~~~~~~~~~~~~~
1098 When importing a renamed file or directory, simply delete the old
1099 name(s) and modify the new name(s) during the corresponding commit.
1100 Git performs rename detection after-the-fact, rather than explicitly
1101 during a commit.
1103 Use Tag Fixup Branches
1104 ~~~~~~~~~~~~~~~~~~~~~~
1105 Some other SCM systems let the user create a tag from multiple
1106 files which are not from the same commit/changeset. Or to create
1107 tags which are a subset of the files available in the repository.
1109 Importing these tags as-is in Git is impossible without making at
1110 least one commit which ``fixes up'' the files to match the content
1111 of the tag. Use fast-import's `reset` command to reset a dummy branch
1112 outside of your normal branch space to the base commit for the tag,
1113 then commit one or more file fixup commits, and finally tag the
1114 dummy branch.
1116 For example since all normal branches are stored under `refs/heads/`
1117 name the tag fixup branch `TAG_FIXUP`. This way it is impossible for
1118 the fixup branch used by the importer to have namespace conflicts
1119 with real branches imported from the source (the name `TAG_FIXUP`
1120 is not `refs/heads/TAG_FIXUP`).
1122 When committing fixups, consider using `merge` to connect the
1123 commit(s) which are supplying file revisions to the fixup branch.
1124 Doing so will allow tools such as 'git blame' to track
1125 through the real commit history and properly annotate the source
1126 files.
1128 After fast-import terminates the frontend will need to do `rm .git/TAG_FIXUP`
1129 to remove the dummy branch.
1131 Import Now, Repack Later
1132 ~~~~~~~~~~~~~~~~~~~~~~~~
1133 As soon as fast-import completes the Git repository is completely valid
1134 and ready for use. Typically this takes only a very short time,
1135 even for considerably large projects (100,000+ commits).
1137 However repacking the repository is necessary to improve data
1138 locality and access performance. It can also take hours on extremely
1139 large projects (especially if -f and a large \--window parameter is
1140 used). Since repacking is safe to run alongside readers and writers,
1141 run the repack in the background and let it finish when it finishes.
1142 There is no reason to wait to explore your new Git project!
1144 If you choose to wait for the repack, don't try to run benchmarks
1145 or performance tests until repacking is completed. fast-import outputs
1146 suboptimal packfiles that are simply never seen in real use
1147 situations.
1149 Repacking Historical Data
1150 ~~~~~~~~~~~~~~~~~~~~~~~~~
1151 If you are repacking very old imported data (e.g. older than the
1152 last year), consider expending some extra CPU time and supplying
1153 \--window=50 (or higher) when you run 'git repack'.
1154 This will take longer, but will also produce a smaller packfile.
1155 You only need to expend the effort once, and everyone using your
1156 project will benefit from the smaller repository.
1158 Include Some Progress Messages
1159 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1160 Every once in a while have your frontend emit a `progress` message
1161 to fast-import. The contents of the messages are entirely free-form,
1162 so one suggestion would be to output the current month and year
1163 each time the current commit date moves into the next month.
1164 Your users will feel better knowing how much of the data stream
1165 has been processed.
1168 Packfile Optimization
1169 ---------------------
1170 When packing a blob fast-import always attempts to deltify against the last
1171 blob written. Unless specifically arranged for by the frontend,
1172 this will probably not be a prior version of the same file, so the
1173 generated delta will not be the smallest possible. The resulting
1174 packfile will be compressed, but will not be optimal.
1176 Frontends which have efficient access to all revisions of a
1177 single file (for example reading an RCS/CVS ,v file) can choose
1178 to supply all revisions of that file as a sequence of consecutive
1179 `blob` commands. This allows fast-import to deltify the different file
1180 revisions against each other, saving space in the final packfile.
1181 Marks can be used to later identify individual file revisions during
1182 a sequence of `commit` commands.
1184 The packfile(s) created by fast-import do not encourage good disk access
1185 patterns. This is caused by fast-import writing the data in the order
1186 it is received on standard input, while Git typically organizes
1187 data within packfiles to make the most recent (current tip) data
1188 appear before historical data. Git also clusters commits together,
1189 speeding up revision traversal through better cache locality.
1191 For this reason it is strongly recommended that users repack the
1192 repository with `git repack -a -d` after fast-import completes, allowing
1193 Git to reorganize the packfiles for faster data access. If blob
1194 deltas are suboptimal (see above) then also adding the `-f` option
1195 to force recomputation of all deltas can significantly reduce the
1196 final packfile size (30-50% smaller can be quite typical).
1199 Memory Utilization
1200 ------------------
1201 There are a number of factors which affect how much memory fast-import
1202 requires to perform an import. Like critical sections of core
1203 Git, fast-import uses its own memory allocators to amortize any overheads
1204 associated with malloc. In practice fast-import tends to amortize any
1205 malloc overheads to 0, due to its use of large block allocations.
1207 per object
1208 ~~~~~~~~~~
1209 fast-import maintains an in-memory structure for every object written in
1210 this execution. On a 32 bit system the structure is 32 bytes,
1211 on a 64 bit system the structure is 40 bytes (due to the larger
1212 pointer sizes). Objects in the table are not deallocated until
1213 fast-import terminates. Importing 2 million objects on a 32 bit system
1214 will require approximately 64 MiB of memory.
1216 The object table is actually a hashtable keyed on the object name
1217 (the unique SHA-1). This storage configuration allows fast-import to reuse
1218 an existing or already written object and avoid writing duplicates
1219 to the output packfile. Duplicate blobs are surprisingly common
1220 in an import, typically due to branch merges in the source.
1222 per mark
1223 ~~~~~~~~
1224 Marks are stored in a sparse array, using 1 pointer (4 bytes or 8
1225 bytes, depending on pointer size) per mark. Although the array
1226 is sparse, frontends are still strongly encouraged to use marks
1227 between 1 and n, where n is the total number of marks required for
1228 this import.
1230 per branch
1231 ~~~~~~~~~~
1232 Branches are classified as active and inactive. The memory usage
1233 of the two classes is significantly different.
1235 Inactive branches are stored in a structure which uses 96 or 120
1236 bytes (32 bit or 64 bit systems, respectively), plus the length of
1237 the branch name (typically under 200 bytes), per branch. fast-import will
1238 easily handle as many as 10,000 inactive branches in under 2 MiB
1239 of memory.
1241 Active branches have the same overhead as inactive branches, but
1242 also contain copies of every tree that has been recently modified on
1243 that branch. If subtree `include` has not been modified since the
1244 branch became active, its contents will not be loaded into memory,
1245 but if subtree `src` has been modified by a commit since the branch
1246 became active, then its contents will be loaded in memory.
1248 As active branches store metadata about the files contained on that
1249 branch, their in-memory storage size can grow to a considerable size
1250 (see below).
1252 fast-import automatically moves active branches to inactive status based on
1253 a simple least-recently-used algorithm. The LRU chain is updated on
1254 each `commit` command. The maximum number of active branches can be
1255 increased or decreased on the command line with \--active-branches=.
1257 per active tree
1258 ~~~~~~~~~~~~~~~
1259 Trees (aka directories) use just 12 bytes of memory on top of the
1260 memory required for their entries (see ``per active file'' below).
1261 The cost of a tree is virtually 0, as its overhead amortizes out
1262 over the individual file entries.
1264 per active file entry
1265 ~~~~~~~~~~~~~~~~~~~~~
1266 Files (and pointers to subtrees) within active trees require 52 or 64
1267 bytes (32/64 bit platforms) per entry. To conserve space, file and
1268 tree names are pooled in a common string table, allowing the filename
1269 ``Makefile'' to use just 16 bytes (after including the string header
1270 overhead) no matter how many times it occurs within the project.
1272 The active branch LRU, when coupled with the filename string pool
1273 and lazy loading of subtrees, allows fast-import to efficiently import
1274 projects with 2,000+ branches and 45,114+ files in a very limited
1275 memory footprint (less than 2.7 MiB per active branch).
1277 Signals
1278 -------
1279 Sending *SIGUSR1* to the 'git fast-import' process ends the current
1280 packfile early, simulating a `checkpoint` command. The impatient
1281 operator can use this facility to peek at the objects and refs from an
1282 import in progress, at the cost of some added running time and worse
1283 compression.
1285 Author
1286 ------
1287 Written by Shawn O. Pearce <>.
1289 Documentation
1290 --------------
1291 Documentation by Shawn O. Pearce <>.
1293 GIT
1294 ---
1295 Part of the linkgit:git[1] suite