Merge branch 'maint-1.7.3' into maint-1.7.4
[git/git.git] / Documentation / git-fast-import.txt
1 git-fast-import(1)
2 ==================
3
4 NAME
5 ----
6 git-fast-import - Backend for fast Git data importers
7
8
9 SYNOPSIS
10 --------
11 frontend | 'git fast-import' [options]
12
13 DESCRIPTION
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'.
19
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.
25
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.
31
32
33 OPTIONS
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.
40
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).
45
46 --max-pack-size=<n>::
47 Maximum size of each output packfile.
48 The default is unlimited.
49
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.
55
56 --depth=<n>::
57 Maximum delta depth, for blob and tree deltification.
58 Default is 10.
59
60 --active-branches=<n>::
61 Maximum number of branches to maintain active at once.
62 See ``Memory Utilization'' below for details. Default is 5.
63
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.
72
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.
80
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.
88
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.
94
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`.
99
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'.
108
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.
113
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.
119
120
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.
129
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).
135
136
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).
145
146
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).
153
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.
162
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.
166
167
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.
176
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.
185
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.
193
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.
200
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.
209
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.
215
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.
239
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.
268
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`.
289
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.
295
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.
300
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.
306
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.
311
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.
316
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.
322
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.
327
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.
332
333 `feature`::
334 Require that fast-import supports the specified feature, or
335 abort if it does not.
336
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.
341
342 `commit`
343 ~~~~~~~~
344 Create or update a branch with a new commit, recording one logical
345 change to the project.
346
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 ....
358
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.
365
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.
371
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.
377
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).
385
386 The `LF` after the command is optional (it used to be required).
387
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`.
395
396 `committer`
397 ^^^^^^^^^^^
398 The `committer` command indicates who made this commit, and when
399 they made it.
400
401 Here `<name>` is the person's display name (for example
402 ``Com M Itter'') and `<email>` is the person's email address
403 (``cm@example.com''). `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.
408
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.
413
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.
419
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.
429
430 As `LF` is not valid in a Git refname or SHA-1 expression, no
431 quoting or escaping syntax is supported within `<committish>`.
432
433 Here `<committish>` is any of the following:
434
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.
438
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.
448
449 * A complete 40 byte or abbreviated commit SHA-1 in hex.
450
451 * Any valid Git SHA-1 expression that resolves to a commit. See
452 ``SPECIFYING REVISIONS'' in linkgit:gitrevisions[7] for details.
453
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.
465
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.
477
478 Here `<committish>` is any of the commit specification expressions
479 also accepted by `from` (see above).
480
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.
486
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`.
500
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.
512
513 In both formats `<mode>` is the type of file entry, specified
514 in octal. Git only supports the following modes:
515
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`.
526
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).
529
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 (`"`).
533
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"`.
536
537 The value of `<path>` must be in canonical form. That is it must not:
538
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).
544
545 The root of the tree can be represented by an empty string as `<path>`.
546
547 It is recommended that `<path>` always be encoded using UTF-8.
548
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.
556
557 ....
558 'D' SP <path> LF
559 ....
560
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>`.
564
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.
571
572 ....
573 'C' SP <path> SP <path> LF
574 ....
575
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.
580
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.
585
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.
591
592 ....
593 'R' SP <path> SP <path> LF
594 ....
595
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.
600
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.
605
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`.
614
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.
621
622 ....
623 'deleteall' LF
624 ....
625
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.
630
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.
638
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.
644
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.
657
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.
669
670 In both formats `<committish>` is any of the commit specification
671 expressions also accepted by `from` (see above).
672
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.
680
681 ....
682 'mark' SP ':' <idnum> LF
683 ....
684
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.
689
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.
693
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.
698
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 ....
705
706 where `<name>` is the name of the tag to create.
707
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`.
712
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.
716
717 The `from` command is the same as in the `commit` command; see
718 above for details.
719
720 The `tagger` command uses the same format as `committer` within
721 `commit`; again see above for details.
722
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.
728
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.
736
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.
743
744 ....
745 'reset' SP <ref> LF
746 ('from' SP <committish> LF)?
747 LF?
748 ....
749
750 For a detailed description of `<ref>` and `<committish>` see above
751 under `commit` and `from`.
752
753 The `LF` after the command is optional (it used to be required).
754
755 The `reset` command can also be used to create lightweight
756 (non-annotated) tags. For example:
757
758 ====
759 reset refs/tags/938
760 from :938
761 ====
762
763 would create the lightweight tag `refs/tags/938` referring to
764 whatever commit mark `:938` references.
765
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.
772
773 ....
774 'blob' LF
775 mark?
776 data
777 ....
778
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.
783
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.
792
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 `#`.
797
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`.
815
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).
837
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.
842
843 ....
844 'checkpoint' LF
845 LF?
846 ....
847
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.
852
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.
857
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.
863
864 The `LF` after the command is optional (it used to be required).
865
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.
872
873 ....
874 'progress' SP <any> LF
875 LF?
876 ....
877
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:
882
883 ====
884 frontend | git fast-import | sed 's/^progress //'
885 ====
886
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.
890
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.
898
899 ....
900 'cat-blob' SP <dataref> LF
901 ....
902
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.
906
907 Output uses the same format as `git cat-file --batch`:
908
909 ====
910 <sha1> SP 'blob' SP <size> LF
911 <contents> LF
912 ====
913
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.
917
918 `feature`
919 ~~~~~~~~~
920 Require that fast-import supports the specified feature, or abort if
921 it does not.
922
923 ....
924 'feature' SP <feature> ('=' <argument>)? LF
925 ....
926
927 The <feature> part of the command may be any one of the following:
928
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).
937
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.
943
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.
950
951 notes::
952 Require that the backend support the 'notemodify' (N)
953 subcommand to the 'commit' command.
954 Versions of fast-import not supporting notes will exit
955 with a message indicating so.
956
957
958 `option`
959 ~~~~~~~~
960 Processes the specified option so that git fast-import behaves in a
961 way that suits the frontend's needs.
962 Note that options specified by the frontend are overridden by any
963 options the user may specify to git fast-import itself.
964
965 ....
966 'option' SP <option> LF
967 ....
968
969 The `<option>` part of the command may contain any of the options
970 listed in the OPTIONS section that do not change import semantics,
971 without the leading '--' and is treated in the same way.
972
973 Option commands must be the first commands on the input (not counting
974 feature commands), to give an option command after any non-option
975 command is an error.
976
977 The following commandline options change import semantics and may therefore
978 not be passed as option:
979
980 * date-format
981 * import-marks
982 * export-marks
983 * cat-blob-fd
984 * force
985
986 Crash Reports
987 -------------
988 If fast-import is supplied invalid input it will terminate with a
989 non-zero exit status and create a crash report in the top level of
990 the Git repository it was importing into. Crash reports contain
991 a snapshot of the internal fast-import state as well as the most
992 recent commands that lead up to the crash.
993
994 All recent commands (including stream comments, file changes and
995 progress commands) are shown in the command history within the crash
996 report, but raw file data and commit messages are excluded from the
997 crash report. This exclusion saves space within the report file
998 and reduces the amount of buffering that fast-import must perform
999 during execution.
1000
1001 After writing a crash report fast-import will close the current
1002 packfile and export the marks table. This allows the frontend
1003 developer to inspect the repository state and resume the import from
1004 the point where it crashed. The modified branches and tags are not
1005 updated during a crash, as the import did not complete successfully.
1006 Branch and tag information can be found in the crash report and
1007 must be applied manually if the update is needed.
1008
1009 An example crash:
1010
1011 ====
1012 $ cat >in <<END_OF_INPUT
1013 # my very first test commit
1014 commit refs/heads/master
1015 committer Shawn O. Pearce <spearce> 19283 -0400
1016 # who is that guy anyway?
1017 data <<EOF
1018 this is my commit
1019 EOF
1020 M 644 inline .gitignore
1021 data <<EOF
1022 .gitignore
1023 EOF
1024 M 777 inline bob
1025 END_OF_INPUT
1026
1027 $ git fast-import <in
1028 fatal: Corrupt mode: M 777 inline bob
1029 fast-import: dumping crash report to .git/fast_import_crash_8434
1030
1031 $ cat .git/fast_import_crash_8434
1032 fast-import crash report:
1033 fast-import process: 8434
1034 parent process : 1391
1035 at Sat Sep 1 00:58:12 2007
1036
1037 fatal: Corrupt mode: M 777 inline bob
1038
1039 Most Recent Commands Before Crash
1040 ---------------------------------
1041 # my very first test commit
1042 commit refs/heads/master
1043 committer Shawn O. Pearce <spearce> 19283 -0400
1044 # who is that guy anyway?
1045 data <<EOF
1046 M 644 inline .gitignore
1047 data <<EOF
1048 * M 777 inline bob
1049
1050 Active Branch LRU
1051 -----------------
1052 active_branches = 1 cur, 5 max
1053
1054 pos clock name
1055 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1056 1) 0 refs/heads/master
1057
1058 Inactive Branches
1059 -----------------
1060 refs/heads/master:
1061 status : active loaded dirty
1062 tip commit : 0000000000000000000000000000000000000000
1063 old tree : 0000000000000000000000000000000000000000
1064 cur tree : 0000000000000000000000000000000000000000
1065 commit clock: 0
1066 last pack :
1067
1068
1069 -------------------
1070 END OF CRASH REPORT
1071 ====
1072
1073 Tips and Tricks
1074 ---------------
1075 The following tips and tricks have been collected from various
1076 users of fast-import, and are offered here as suggestions.
1077
1078 Use One Mark Per Commit
1079 ~~~~~~~~~~~~~~~~~~~~~~~
1080 When doing a repository conversion, use a unique mark per commit
1081 (`mark :<n>`) and supply the \--export-marks option on the command
1082 line. fast-import will dump a file which lists every mark and the Git
1083 object SHA-1 that corresponds to it. If the frontend can tie
1084 the marks back to the source repository, it is easy to verify the
1085 accuracy and completeness of the import by comparing each Git
1086 commit to the corresponding source revision.
1087
1088 Coming from a system such as Perforce or Subversion this should be
1089 quite simple, as the fast-import mark can also be the Perforce changeset
1090 number or the Subversion revision number.
1091
1092 Freely Skip Around Branches
1093 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
1094 Don't bother trying to optimize the frontend to stick to one branch
1095 at a time during an import. Although doing so might be slightly
1096 faster for fast-import, it tends to increase the complexity of the frontend
1097 code considerably.
1098
1099 The branch LRU builtin to fast-import tends to behave very well, and the
1100 cost of activating an inactive branch is so low that bouncing around
1101 between branches has virtually no impact on import performance.
1102
1103 Handling Renames
1104 ~~~~~~~~~~~~~~~~
1105 When importing a renamed file or directory, simply delete the old
1106 name(s) and modify the new name(s) during the corresponding commit.
1107 Git performs rename detection after-the-fact, rather than explicitly
1108 during a commit.
1109
1110 Use Tag Fixup Branches
1111 ~~~~~~~~~~~~~~~~~~~~~~
1112 Some other SCM systems let the user create a tag from multiple
1113 files which are not from the same commit/changeset. Or to create
1114 tags which are a subset of the files available in the repository.
1115
1116 Importing these tags as-is in Git is impossible without making at
1117 least one commit which ``fixes up'' the files to match the content
1118 of the tag. Use fast-import's `reset` command to reset a dummy branch
1119 outside of your normal branch space to the base commit for the tag,
1120 then commit one or more file fixup commits, and finally tag the
1121 dummy branch.
1122
1123 For example since all normal branches are stored under `refs/heads/`
1124 name the tag fixup branch `TAG_FIXUP`. This way it is impossible for
1125 the fixup branch used by the importer to have namespace conflicts
1126 with real branches imported from the source (the name `TAG_FIXUP`
1127 is not `refs/heads/TAG_FIXUP`).
1128
1129 When committing fixups, consider using `merge` to connect the
1130 commit(s) which are supplying file revisions to the fixup branch.
1131 Doing so will allow tools such as 'git blame' to track
1132 through the real commit history and properly annotate the source
1133 files.
1134
1135 After fast-import terminates the frontend will need to do `rm .git/TAG_FIXUP`
1136 to remove the dummy branch.
1137
1138 Import Now, Repack Later
1139 ~~~~~~~~~~~~~~~~~~~~~~~~
1140 As soon as fast-import completes the Git repository is completely valid
1141 and ready for use. Typically this takes only a very short time,
1142 even for considerably large projects (100,000+ commits).
1143
1144 However repacking the repository is necessary to improve data
1145 locality and access performance. It can also take hours on extremely
1146 large projects (especially if -f and a large \--window parameter is
1147 used). Since repacking is safe to run alongside readers and writers,
1148 run the repack in the background and let it finish when it finishes.
1149 There is no reason to wait to explore your new Git project!
1150
1151 If you choose to wait for the repack, don't try to run benchmarks
1152 or performance tests until repacking is completed. fast-import outputs
1153 suboptimal packfiles that are simply never seen in real use
1154 situations.
1155
1156 Repacking Historical Data
1157 ~~~~~~~~~~~~~~~~~~~~~~~~~
1158 If you are repacking very old imported data (e.g. older than the
1159 last year), consider expending some extra CPU time and supplying
1160 \--window=50 (or higher) when you run 'git repack'.
1161 This will take longer, but will also produce a smaller packfile.
1162 You only need to expend the effort once, and everyone using your
1163 project will benefit from the smaller repository.
1164
1165 Include Some Progress Messages
1166 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1167 Every once in a while have your frontend emit a `progress` message
1168 to fast-import. The contents of the messages are entirely free-form,
1169 so one suggestion would be to output the current month and year
1170 each time the current commit date moves into the next month.
1171 Your users will feel better knowing how much of the data stream
1172 has been processed.
1173
1174
1175 Packfile Optimization
1176 ---------------------
1177 When packing a blob fast-import always attempts to deltify against the last
1178 blob written. Unless specifically arranged for by the frontend,
1179 this will probably not be a prior version of the same file, so the
1180 generated delta will not be the smallest possible. The resulting
1181 packfile will be compressed, but will not be optimal.
1182
1183 Frontends which have efficient access to all revisions of a
1184 single file (for example reading an RCS/CVS ,v file) can choose
1185 to supply all revisions of that file as a sequence of consecutive
1186 `blob` commands. This allows fast-import to deltify the different file
1187 revisions against each other, saving space in the final packfile.
1188 Marks can be used to later identify individual file revisions during
1189 a sequence of `commit` commands.
1190
1191 The packfile(s) created by fast-import do not encourage good disk access
1192 patterns. This is caused by fast-import writing the data in the order
1193 it is received on standard input, while Git typically organizes
1194 data within packfiles to make the most recent (current tip) data
1195 appear before historical data. Git also clusters commits together,
1196 speeding up revision traversal through better cache locality.
1197
1198 For this reason it is strongly recommended that users repack the
1199 repository with `git repack -a -d` after fast-import completes, allowing
1200 Git to reorganize the packfiles for faster data access. If blob
1201 deltas are suboptimal (see above) then also adding the `-f` option
1202 to force recomputation of all deltas can significantly reduce the
1203 final packfile size (30-50% smaller can be quite typical).
1204
1205
1206 Memory Utilization
1207 ------------------
1208 There are a number of factors which affect how much memory fast-import
1209 requires to perform an import. Like critical sections of core
1210 Git, fast-import uses its own memory allocators to amortize any overheads
1211 associated with malloc. In practice fast-import tends to amortize any
1212 malloc overheads to 0, due to its use of large block allocations.
1213
1214 per object
1215 ~~~~~~~~~~
1216 fast-import maintains an in-memory structure for every object written in
1217 this execution. On a 32 bit system the structure is 32 bytes,
1218 on a 64 bit system the structure is 40 bytes (due to the larger
1219 pointer sizes). Objects in the table are not deallocated until
1220 fast-import terminates. Importing 2 million objects on a 32 bit system
1221 will require approximately 64 MiB of memory.
1222
1223 The object table is actually a hashtable keyed on the object name
1224 (the unique SHA-1). This storage configuration allows fast-import to reuse
1225 an existing or already written object and avoid writing duplicates
1226 to the output packfile. Duplicate blobs are surprisingly common
1227 in an import, typically due to branch merges in the source.
1228
1229 per mark
1230 ~~~~~~~~
1231 Marks are stored in a sparse array, using 1 pointer (4 bytes or 8
1232 bytes, depending on pointer size) per mark. Although the array
1233 is sparse, frontends are still strongly encouraged to use marks
1234 between 1 and n, where n is the total number of marks required for
1235 this import.
1236
1237 per branch
1238 ~~~~~~~~~~
1239 Branches are classified as active and inactive. The memory usage
1240 of the two classes is significantly different.
1241
1242 Inactive branches are stored in a structure which uses 96 or 120
1243 bytes (32 bit or 64 bit systems, respectively), plus the length of
1244 the branch name (typically under 200 bytes), per branch. fast-import will
1245 easily handle as many as 10,000 inactive branches in under 2 MiB
1246 of memory.
1247
1248 Active branches have the same overhead as inactive branches, but
1249 also contain copies of every tree that has been recently modified on
1250 that branch. If subtree `include` has not been modified since the
1251 branch became active, its contents will not be loaded into memory,
1252 but if subtree `src` has been modified by a commit since the branch
1253 became active, then its contents will be loaded in memory.
1254
1255 As active branches store metadata about the files contained on that
1256 branch, their in-memory storage size can grow to a considerable size
1257 (see below).
1258
1259 fast-import automatically moves active branches to inactive status based on
1260 a simple least-recently-used algorithm. The LRU chain is updated on
1261 each `commit` command. The maximum number of active branches can be
1262 increased or decreased on the command line with \--active-branches=.
1263
1264 per active tree
1265 ~~~~~~~~~~~~~~~
1266 Trees (aka directories) use just 12 bytes of memory on top of the
1267 memory required for their entries (see ``per active file'' below).
1268 The cost of a tree is virtually 0, as its overhead amortizes out
1269 over the individual file entries.
1270
1271 per active file entry
1272 ~~~~~~~~~~~~~~~~~~~~~
1273 Files (and pointers to subtrees) within active trees require 52 or 64
1274 bytes (32/64 bit platforms) per entry. To conserve space, file and
1275 tree names are pooled in a common string table, allowing the filename
1276 ``Makefile'' to use just 16 bytes (after including the string header
1277 overhead) no matter how many times it occurs within the project.
1278
1279 The active branch LRU, when coupled with the filename string pool
1280 and lazy loading of subtrees, allows fast-import to efficiently import
1281 projects with 2,000+ branches and 45,114+ files in a very limited
1282 memory footprint (less than 2.7 MiB per active branch).
1283
1284 Signals
1285 -------
1286 Sending *SIGUSR1* to the 'git fast-import' process ends the current
1287 packfile early, simulating a `checkpoint` command. The impatient
1288 operator can use this facility to peek at the objects and refs from an
1289 import in progress, at the cost of some added running time and worse
1290 compression.
1291
1292 Author
1293 ------
1294 Written by Shawn O. Pearce <spearce@spearce.org>.
1295
1296 Documentation
1297 --------------
1298 Documentation by Shawn O. Pearce <spearce@spearce.org>.
1299
1300 GIT
1301 ---
1302 Part of the linkgit:git[1] suite