remote-bzr: detect local repositories
[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 [verse]
12 frontend | 'git fast-import' [options]
13
14 DESCRIPTION
15 -----------
16 This program is usually not what the end user wants to run directly.
17 Most end users want to use one of the existing frontend programs,
18 which parses a specific type of foreign source and feeds the contents
19 stored there to 'git fast-import'.
20
21 fast-import reads a mixed command/data stream from standard input and
22 writes one or more packfiles directly into the current repository.
23 When EOF is received on standard input, fast import writes out
24 updated branch and tag refs, fully updating the current repository
25 with the newly imported data.
26
27 The fast-import backend itself can import into an empty repository (one that
28 has already been initialized by 'git init') or incrementally
29 update an existing populated repository. Whether or not incremental
30 imports are supported from a particular foreign source depends on
31 the frontend program in use.
32
33
34 OPTIONS
35 -------
36 --date-format=<fmt>::
37 Specify the type of dates the frontend will supply to
38 fast-import within `author`, `committer` and `tagger` commands.
39 See ``Date Formats'' below for details about which formats
40 are supported, and their syntax.
41
42 -- done::
43 Terminate with error if there is no 'done' command at the
44 end of the stream.
45
46 --force::
47 Force updating modified existing branches, even if doing
48 so would cause commits to be lost (as the new commit does
49 not contain the old commit).
50
51 --max-pack-size=<n>::
52 Maximum size of each output packfile.
53 The default is unlimited.
54
55 --big-file-threshold=<n>::
56 Maximum size of a blob that fast-import will attempt to
57 create a delta for, expressed in bytes. The default is 512m
58 (512 MiB). Some importers may wish to lower this on systems
59 with constrained memory.
60
61 --depth=<n>::
62 Maximum delta depth, for blob and tree deltification.
63 Default is 10.
64
65 --active-branches=<n>::
66 Maximum number of branches to maintain active at once.
67 See ``Memory Utilization'' below for details. Default is 5.
68
69 --export-marks=<file>::
70 Dumps the internal marks table to <file> when complete.
71 Marks are written one per line as `:markid SHA-1`.
72 Frontends can use this file to validate imports after they
73 have been completed, or to save the marks table across
74 incremental runs. As <file> is only opened and truncated
75 at checkpoint (or completion) the same path can also be
76 safely given to \--import-marks.
77
78 --import-marks=<file>::
79 Before processing any input, load the marks specified in
80 <file>. The input file must exist, must be readable, and
81 must use the same format as produced by \--export-marks.
82 Multiple options may be supplied to import more than one
83 set of marks. If a mark is defined to different values,
84 the last file wins.
85
86 --import-marks-if-exists=<file>::
87 Like --import-marks but instead of erroring out, silently
88 skips the file if it does not exist.
89
90 --relative-marks::
91 After specifying --relative-marks the paths specified
92 with --import-marks= and --export-marks= are relative
93 to an internal directory in the current repository.
94 In git-fast-import this means that the paths are relative
95 to the .git/info/fast-import directory. However, other
96 importers may use a different location.
97
98 --no-relative-marks::
99 Negates a previous --relative-marks. Allows for combining
100 relative and non-relative marks by interweaving
101 --(no-)-relative-marks with the --(import|export)-marks=
102 options.
103
104 --cat-blob-fd=<fd>::
105 Write responses to `cat-blob` and `ls` queries to the
106 file descriptor <fd> instead of `stdout`. Allows `progress`
107 output intended for the end-user to be separated from other
108 output.
109
110 --done::
111 Require a `done` command at the end of the stream.
112 This option might be useful for detecting errors that
113 cause the frontend to terminate before it has started to
114 write a stream.
115
116 --export-pack-edges=<file>::
117 After creating a packfile, print a line of data to
118 <file> listing the filename of the packfile and the last
119 commit on each branch that was written to that packfile.
120 This information may be useful after importing projects
121 whose total object set exceeds the 4 GiB packfile limit,
122 as these commits can be used as edge points during calls
123 to 'git pack-objects'.
124
125 --quiet::
126 Disable all non-fatal output, making fast-import silent when it
127 is successful. This option disables the output shown by
128 \--stats.
129
130 --stats::
131 Display some basic statistics about the objects fast-import has
132 created, the packfiles they were stored into, and the
133 memory used by fast-import during this run. Showing this output
134 is currently the default, but can be disabled with \--quiet.
135
136
137 Performance
138 -----------
139 The design of fast-import allows it to import large projects in a minimum
140 amount of memory usage and processing time. Assuming the frontend
141 is able to keep up with fast-import and feed it a constant stream of data,
142 import times for projects holding 10+ years of history and containing
143 100,000+ individual commits are generally completed in just 1-2
144 hours on quite modest (~$2,000 USD) hardware.
145
146 Most bottlenecks appear to be in foreign source data access (the
147 source just cannot extract revisions fast enough) or disk IO (fast-import
148 writes as fast as the disk will take the data). Imports will run
149 faster if the source data is stored on a different drive than the
150 destination Git repository (due to less IO contention).
151
152
153 Development Cost
154 ----------------
155 A typical frontend for fast-import tends to weigh in at approximately 200
156 lines of Perl/Python/Ruby code. Most developers have been able to
157 create working importers in just a couple of hours, even though it
158 is their first exposure to fast-import, and sometimes even to Git. This is
159 an ideal situation, given that most conversion tools are throw-away
160 (use once, and never look back).
161
162
163 Parallel Operation
164 ------------------
165 Like 'git push' or 'git fetch', imports handled by fast-import are safe to
166 run alongside parallel `git repack -a -d` or `git gc` invocations,
167 or any other Git operation (including 'git prune', as loose objects
168 are never used by fast-import).
169
170 fast-import does not lock the branch or tag refs it is actively importing.
171 After the import, during its ref update phase, fast-import tests each
172 existing branch ref to verify the update will be a fast-forward
173 update (the commit stored in the ref is contained in the new
174 history of the commit to be written). If the update is not a
175 fast-forward update, fast-import will skip updating that ref and instead
176 prints a warning message. fast-import will always attempt to update all
177 branch refs, and does not stop on the first failure.
178
179 Branch updates can be forced with \--force, but it's recommended that
180 this only be used on an otherwise quiet repository. Using \--force
181 is not necessary for an initial import into an empty repository.
182
183
184 Technical Discussion
185 --------------------
186 fast-import tracks a set of branches in memory. Any branch can be created
187 or modified at any point during the import process by sending a
188 `commit` command on the input stream. This design allows a frontend
189 program to process an unlimited number of branches simultaneously,
190 generating commits in the order they are available from the source
191 data. It also simplifies the frontend programs considerably.
192
193 fast-import does not use or alter the current working directory, or any
194 file within it. (It does however update the current Git repository,
195 as referenced by `GIT_DIR`.) Therefore an import frontend may use
196 the working directory for its own purposes, such as extracting file
197 revisions from the foreign source. This ignorance of the working
198 directory also allows fast-import to run very quickly, as it does not
199 need to perform any costly file update operations when switching
200 between branches.
201
202 Input Format
203 ------------
204 With the exception of raw file data (which Git does not interpret)
205 the fast-import input format is text (ASCII) based. This text based
206 format simplifies development and debugging of frontend programs,
207 especially when a higher level language such as Perl, Python or
208 Ruby is being used.
209
210 fast-import is very strict about its input. Where we say SP below we mean
211 *exactly* one space. Likewise LF means one (and only one) linefeed
212 and HT one (and only one) horizontal tab.
213 Supplying additional whitespace characters will cause unexpected
214 results, such as branch names or file names with leading or trailing
215 spaces in their name, or early termination of fast-import when it encounters
216 unexpected input.
217
218 Stream Comments
219 ~~~~~~~~~~~~~~~
220 To aid in debugging frontends fast-import ignores any line that
221 begins with `#` (ASCII pound/hash) up to and including the line
222 ending `LF`. A comment line may contain any sequence of bytes
223 that does not contain an LF and therefore may be used to include
224 any detailed debugging information that might be specific to the
225 frontend and useful when inspecting a fast-import data stream.
226
227 Date Formats
228 ~~~~~~~~~~~~
229 The following date formats are supported. A frontend should select
230 the format it will use for this import by passing the format name
231 in the \--date-format=<fmt> command line option.
232
233 `raw`::
234 This is the Git native format and is `<time> SP <offutc>`.
235 It is also fast-import's default format, if \--date-format was
236 not specified.
237 +
238 The time of the event is specified by `<time>` as the number of
239 seconds since the UNIX epoch (midnight, Jan 1, 1970, UTC) and is
240 written as an ASCII decimal integer.
241 +
242 The local offset is specified by `<offutc>` as a positive or negative
243 offset from UTC. For example EST (which is 5 hours behind UTC)
244 would be expressed in `<tz>` by ``-0500'' while UTC is ``+0000''.
245 The local offset does not affect `<time>`; it is used only as an
246 advisement to help formatting routines display the timestamp.
247 +
248 If the local offset is not available in the source material, use
249 ``+0000'', or the most common local offset. For example many
250 organizations have a CVS repository which has only ever been accessed
251 by users who are located in the same location and timezone. In this
252 case a reasonable offset from UTC could be assumed.
253 +
254 Unlike the `rfc2822` format, this format is very strict. Any
255 variation in formatting will cause fast-import to reject the value.
256
257 `rfc2822`::
258 This is the standard email format as described by RFC 2822.
259 +
260 An example value is ``Tue Feb 6 11:22:18 2007 -0500''. The Git
261 parser is accurate, but a little on the lenient side. It is the
262 same parser used by 'git am' when applying patches
263 received from email.
264 +
265 Some malformed strings may be accepted as valid dates. In some of
266 these cases Git will still be able to obtain the correct date from
267 the malformed string. There are also some types of malformed
268 strings which Git will parse wrong, and yet consider valid.
269 Seriously malformed strings will be rejected.
270 +
271 Unlike the `raw` format above, the timezone/UTC offset information
272 contained in an RFC 2822 date string is used to adjust the date
273 value to UTC prior to storage. Therefore it is important that
274 this information be as accurate as possible.
275 +
276 If the source material uses RFC 2822 style dates,
277 the frontend should let fast-import handle the parsing and conversion
278 (rather than attempting to do it itself) as the Git parser has
279 been well tested in the wild.
280 +
281 Frontends should prefer the `raw` format if the source material
282 already uses UNIX-epoch format, can be coaxed to give dates in that
283 format, or its format is easily convertible to it, as there is no
284 ambiguity in parsing.
285
286 `now`::
287 Always use the current time and timezone. The literal
288 `now` must always be supplied for `<when>`.
289 +
290 This is a toy format. The current time and timezone of this system
291 is always copied into the identity string at the time it is being
292 created by fast-import. There is no way to specify a different time or
293 timezone.
294 +
295 This particular format is supplied as it's short to implement and
296 may be useful to a process that wants to create a new commit
297 right now, without needing to use a working directory or
298 'git update-index'.
299 +
300 If separate `author` and `committer` commands are used in a `commit`
301 the timestamps may not match, as the system clock will be polled
302 twice (once for each command). The only way to ensure that both
303 author and committer identity information has the same timestamp
304 is to omit `author` (thus copying from `committer`) or to use a
305 date format other than `now`.
306
307 Commands
308 ~~~~~~~~
309 fast-import accepts several commands to update the current repository
310 and control the current import process. More detailed discussion
311 (with examples) of each command follows later.
312
313 `commit`::
314 Creates a new branch or updates an existing branch by
315 creating a new commit and updating the branch to point at
316 the newly created commit.
317
318 `tag`::
319 Creates an annotated tag object from an existing commit or
320 branch. Lightweight tags are not supported by this command,
321 as they are not recommended for recording meaningful points
322 in time.
323
324 `reset`::
325 Reset an existing branch (or a new branch) to a specific
326 revision. This command must be used to change a branch to
327 a specific revision without making a commit on it.
328
329 `blob`::
330 Convert raw file data into a blob, for future use in a
331 `commit` command. This command is optional and is not
332 needed to perform an import.
333
334 `checkpoint`::
335 Forces fast-import to close the current packfile, generate its
336 unique SHA-1 checksum and index, and start a new packfile.
337 This command is optional and is not needed to perform
338 an import.
339
340 `progress`::
341 Causes fast-import to echo the entire line to its own
342 standard output. This command is optional and is not needed
343 to perform an import.
344
345 `done`::
346 Marks the end of the stream. This command is optional
347 unless the `done` feature was requested using the
348 `--done` command line option or `feature done` command.
349
350 `cat-blob`::
351 Causes fast-import to print a blob in 'cat-file --batch'
352 format to the file descriptor set with `--cat-blob-fd` or
353 `stdout` if unspecified.
354
355 `ls`::
356 Causes fast-import to print a line describing a directory
357 entry in 'ls-tree' format to the file descriptor set with
358 `--cat-blob-fd` or `stdout` if unspecified.
359
360 `feature`::
361 Require that fast-import supports the specified feature, or
362 abort if it does not.
363
364 `option`::
365 Specify any of the options listed under OPTIONS that do not
366 change stream semantic to suit the frontend's needs. This
367 command is optional and is not needed to perform an import.
368
369 `commit`
370 ~~~~~~~~
371 Create or update a branch with a new commit, recording one logical
372 change to the project.
373
374 ....
375 'commit' SP <ref> LF
376 mark?
377 ('author' (SP <name>)? SP LT <email> GT SP <when> LF)?
378 'committer' (SP <name>)? SP LT <email> GT SP <when> LF
379 data
380 ('from' SP <committish> LF)?
381 ('merge' SP <committish> LF)?
382 (filemodify | filedelete | filecopy | filerename | filedeleteall | notemodify)*
383 LF?
384 ....
385
386 where `<ref>` is the name of the branch to make the commit on.
387 Typically branch names are prefixed with `refs/heads/` in
388 Git, so importing the CVS branch symbol `RELENG-1_0` would use
389 `refs/heads/RELENG-1_0` for the value of `<ref>`. The value of
390 `<ref>` must be a valid refname in Git. As `LF` is not valid in
391 a Git refname, no quoting or escaping syntax is supported here.
392
393 A `mark` command may optionally appear, requesting fast-import to save a
394 reference to the newly created commit for future use by the frontend
395 (see below for format). It is very common for frontends to mark
396 every commit they create, thereby allowing future branch creation
397 from any imported commit.
398
399 The `data` command following `committer` must supply the commit
400 message (see below for `data` command syntax). To import an empty
401 commit message use a 0 length data. Commit messages are free-form
402 and are not interpreted by Git. Currently they must be encoded in
403 UTF-8, as fast-import does not permit other encodings to be specified.
404
405 Zero or more `filemodify`, `filedelete`, `filecopy`, `filerename`,
406 `filedeleteall` and `notemodify` commands
407 may be included to update the contents of the branch prior to
408 creating the commit. These commands may be supplied in any order.
409 However it is recommended that a `filedeleteall` command precede
410 all `filemodify`, `filecopy`, `filerename` and `notemodify` commands in
411 the same commit, as `filedeleteall` wipes the branch clean (see below).
412
413 The `LF` after the command is optional (it used to be required).
414
415 `author`
416 ^^^^^^^^
417 An `author` command may optionally appear, if the author information
418 might differ from the committer information. If `author` is omitted
419 then fast-import will automatically use the committer's information for
420 the author portion of the commit. See below for a description of
421 the fields in `author`, as they are identical to `committer`.
422
423 `committer`
424 ^^^^^^^^^^^
425 The `committer` command indicates who made this commit, and when
426 they made it.
427
428 Here `<name>` is the person's display name (for example
429 ``Com M Itter'') and `<email>` is the person's email address
430 (``cm@example.com''). `LT` and `GT` are the literal less-than (\x3c)
431 and greater-than (\x3e) symbols. These are required to delimit
432 the email address from the other fields in the line. Note that
433 `<name>` and `<email>` are free-form and may contain any sequence
434 of bytes, except `LT`, `GT` and `LF`. `<name>` is typically UTF-8 encoded.
435
436 The time of the change is specified by `<when>` using the date format
437 that was selected by the \--date-format=<fmt> command line option.
438 See ``Date Formats'' above for the set of supported formats, and
439 their syntax.
440
441 `from`
442 ^^^^^^
443 The `from` command is used to specify the commit to initialize
444 this branch from. This revision will be the first ancestor of the
445 new commit.
446
447 Omitting the `from` command in the first commit of a new branch
448 will cause fast-import to create that commit with no ancestor. This
449 tends to be desired only for the initial commit of a project.
450 If the frontend creates all files from scratch when making a new
451 branch, a `merge` command may be used instead of `from` to start
452 the commit with an empty tree.
453 Omitting the `from` command on existing branches is usually desired,
454 as the current commit on that branch is automatically assumed to
455 be the first ancestor of the new commit.
456
457 As `LF` is not valid in a Git refname or SHA-1 expression, no
458 quoting or escaping syntax is supported within `<committish>`.
459
460 Here `<committish>` is any of the following:
461
462 * The name of an existing branch already in fast-import's internal branch
463 table. If fast-import doesn't know the name, it's treated as a SHA-1
464 expression.
465
466 * A mark reference, `:<idnum>`, where `<idnum>` is the mark number.
467 +
468 The reason fast-import uses `:` to denote a mark reference is this character
469 is not legal in a Git branch name. The leading `:` makes it easy
470 to distinguish between the mark 42 (`:42`) and the branch 42 (`42`
471 or `refs/heads/42`), or an abbreviated SHA-1 which happened to
472 consist only of base-10 digits.
473 +
474 Marks must be declared (via `mark`) before they can be used.
475
476 * A complete 40 byte or abbreviated commit SHA-1 in hex.
477
478 * Any valid Git SHA-1 expression that resolves to a commit. See
479 ``SPECIFYING REVISIONS'' in linkgit:gitrevisions[7] for details.
480
481 The special case of restarting an incremental import from the
482 current branch value should be written as:
483 ----
484 from refs/heads/branch^0
485 ----
486 The `^0` suffix is necessary as fast-import does not permit a branch to
487 start from itself, and the branch is created in memory before the
488 `from` command is even read from the input. Adding `^0` will force
489 fast-import to resolve the commit through Git's revision parsing library,
490 rather than its internal branch table, thereby loading in the
491 existing value of the branch.
492
493 `merge`
494 ^^^^^^^
495 Includes one additional ancestor commit. If the `from` command is
496 omitted when creating a new branch, the first `merge` commit will be
497 the first ancestor of the current commit, and the branch will start
498 out with no files. An unlimited number of `merge` commands per
499 commit are permitted by fast-import, thereby establishing an n-way merge.
500 However Git's other tools never create commits with more than 15
501 additional ancestors (forming a 16-way merge). For this reason
502 it is suggested that frontends do not use more than 15 `merge`
503 commands per commit; 16, if starting a new, empty branch.
504
505 Here `<committish>` is any of the commit specification expressions
506 also accepted by `from` (see above).
507
508 `filemodify`
509 ^^^^^^^^^^^^
510 Included in a `commit` command to add a new file or change the
511 content of an existing file. This command has two different means
512 of specifying the content of the file.
513
514 External data format::
515 The data content for the file was already supplied by a prior
516 `blob` command. The frontend just needs to connect it.
517 +
518 ....
519 'M' SP <mode> SP <dataref> SP <path> LF
520 ....
521 +
522 Here usually `<dataref>` must be either a mark reference (`:<idnum>`)
523 set by a prior `blob` command, or a full 40-byte SHA-1 of an
524 existing Git blob object. If `<mode>` is `040000`` then
525 `<dataref>` must be the full 40-byte SHA-1 of an existing
526 Git tree object or a mark reference set with `--import-marks`.
527
528 Inline data format::
529 The data content for the file has not been supplied yet.
530 The frontend wants to supply it as part of this modify
531 command.
532 +
533 ....
534 'M' SP <mode> SP 'inline' SP <path> LF
535 data
536 ....
537 +
538 See below for a detailed description of the `data` command.
539
540 In both formats `<mode>` is the type of file entry, specified
541 in octal. Git only supports the following modes:
542
543 * `100644` or `644`: A normal (not-executable) file. The majority
544 of files in most projects use this mode. If in doubt, this is
545 what you want.
546 * `100755` or `755`: A normal, but executable, file.
547 * `120000`: A symlink, the content of the file will be the link target.
548 * `160000`: A gitlink, SHA-1 of the object refers to a commit in
549 another repository. Git links can only be specified by SHA or through
550 a commit mark. They are used to implement submodules.
551 * `040000`: A subdirectory. Subdirectories can only be specified by
552 SHA or through a tree mark set with `--import-marks`.
553
554 In both formats `<path>` is the complete path of the file to be added
555 (if not already existing) or modified (if already existing).
556
557 A `<path>` string must use UNIX-style directory separators (forward
558 slash `/`), may contain any byte other than `LF`, and must not
559 start with double quote (`"`).
560
561 If an `LF` or double quote must be encoded into `<path>` shell-style
562 quoting should be used, e.g. `"path/with\n and \" in it"`.
563
564 The value of `<path>` must be in canonical form. That is it must not:
565
566 * contain an empty directory component (e.g. `foo//bar` is invalid),
567 * end with a directory separator (e.g. `foo/` is invalid),
568 * start with a directory separator (e.g. `/foo` is invalid),
569 * contain the special component `.` or `..` (e.g. `foo/./bar` and
570 `foo/../bar` are invalid).
571
572 The root of the tree can be represented by an empty string as `<path>`.
573
574 It is recommended that `<path>` always be encoded using UTF-8.
575
576 `filedelete`
577 ^^^^^^^^^^^^
578 Included in a `commit` command to remove a file or recursively
579 delete an entire directory from the branch. If the file or directory
580 removal makes its parent directory empty, the parent directory will
581 be automatically removed too. This cascades up the tree until the
582 first non-empty directory or the root is reached.
583
584 ....
585 'D' SP <path> LF
586 ....
587
588 here `<path>` is the complete path of the file or subdirectory to
589 be removed from the branch.
590 See `filemodify` above for a detailed description of `<path>`.
591
592 `filecopy`
593 ^^^^^^^^^^^^
594 Recursively copies an existing file or subdirectory to a different
595 location within the branch. The existing file or directory must
596 exist. If the destination exists it will be completely replaced
597 by the content copied from the source.
598
599 ....
600 'C' SP <path> SP <path> LF
601 ....
602
603 here the first `<path>` is the source location and the second
604 `<path>` is the destination. See `filemodify` above for a detailed
605 description of what `<path>` may look like. To use a source path
606 that contains SP the path must be quoted.
607
608 A `filecopy` command takes effect immediately. Once the source
609 location has been copied to the destination any future commands
610 applied to the source location will not impact the destination of
611 the copy.
612
613 `filerename`
614 ^^^^^^^^^^^^
615 Renames an existing file or subdirectory to a different location
616 within the branch. The existing file or directory must exist. If
617 the destination exists it will be replaced by the source directory.
618
619 ....
620 'R' SP <path> SP <path> LF
621 ....
622
623 here the first `<path>` is the source location and the second
624 `<path>` is the destination. See `filemodify` above for a detailed
625 description of what `<path>` may look like. To use a source path
626 that contains SP the path must be quoted.
627
628 A `filerename` command takes effect immediately. Once the source
629 location has been renamed to the destination any future commands
630 applied to the source location will create new files there and not
631 impact the destination of the rename.
632
633 Note that a `filerename` is the same as a `filecopy` followed by a
634 `filedelete` of the source location. There is a slight performance
635 advantage to using `filerename`, but the advantage is so small
636 that it is never worth trying to convert a delete/add pair in
637 source material into a rename for fast-import. This `filerename`
638 command is provided just to simplify frontends that already have
639 rename information and don't want bother with decomposing it into a
640 `filecopy` followed by a `filedelete`.
641
642 `filedeleteall`
643 ^^^^^^^^^^^^^^^
644 Included in a `commit` command to remove all files (and also all
645 directories) from the branch. This command resets the internal
646 branch structure to have no files in it, allowing the frontend
647 to subsequently add all interesting files from scratch.
648
649 ....
650 'deleteall' LF
651 ....
652
653 This command is extremely useful if the frontend does not know
654 (or does not care to know) what files are currently on the branch,
655 and therefore cannot generate the proper `filedelete` commands to
656 update the content.
657
658 Issuing a `filedeleteall` followed by the needed `filemodify`
659 commands to set the correct content will produce the same results
660 as sending only the needed `filemodify` and `filedelete` commands.
661 The `filedeleteall` approach may however require fast-import to use slightly
662 more memory per active branch (less than 1 MiB for even most large
663 projects); so frontends that can easily obtain only the affected
664 paths for a commit are encouraged to do so.
665
666 `notemodify`
667 ^^^^^^^^^^^^
668 Included in a `commit` `<notes_ref>` command to add a new note
669 annotating a `<committish>` or change this annotation contents.
670 Internally it is similar to filemodify 100644 on `<committish>`
671 path (maybe split into subdirectories). It's not advised to
672 use any other commands to write to the `<notes_ref>` tree except
673 `filedeleteall` to delete all existing notes in this tree.
674 This command has two different means of specifying the content
675 of the note.
676
677 External data format::
678 The data content for the note was already supplied by a prior
679 `blob` command. The frontend just needs to connect it to the
680 commit that is to be annotated.
681 +
682 ....
683 'N' SP <dataref> SP <committish> LF
684 ....
685 +
686 Here `<dataref>` can be either a mark reference (`:<idnum>`)
687 set by a prior `blob` command, or a full 40-byte SHA-1 of an
688 existing Git blob object.
689
690 Inline data format::
691 The data content for the note has not been supplied yet.
692 The frontend wants to supply it as part of this modify
693 command.
694 +
695 ....
696 'N' SP 'inline' SP <committish> LF
697 data
698 ....
699 +
700 See below for a detailed description of the `data` command.
701
702 In both formats `<committish>` is any of the commit specification
703 expressions also accepted by `from` (see above).
704
705 `mark`
706 ~~~~~~
707 Arranges for fast-import to save a reference to the current object, allowing
708 the frontend to recall this object at a future point in time, without
709 knowing its SHA-1. Here the current object is the object creation
710 command the `mark` command appears within. This can be `commit`,
711 `tag`, and `blob`, but `commit` is the most common usage.
712
713 ....
714 'mark' SP ':' <idnum> LF
715 ....
716
717 where `<idnum>` is the number assigned by the frontend to this mark.
718 The value of `<idnum>` is expressed as an ASCII decimal integer.
719 The value 0 is reserved and cannot be used as
720 a mark. Only values greater than or equal to 1 may be used as marks.
721
722 New marks are created automatically. Existing marks can be moved
723 to another object simply by reusing the same `<idnum>` in another
724 `mark` command.
725
726 `tag`
727 ~~~~~
728 Creates an annotated tag referring to a specific commit. To create
729 lightweight (non-annotated) tags see the `reset` command below.
730
731 ....
732 'tag' SP <name> LF
733 'from' SP <committish> LF
734 'tagger' (SP <name>)? SP LT <email> GT SP <when> LF
735 data
736 ....
737
738 where `<name>` is the name of the tag to create.
739
740 Tag names are automatically prefixed with `refs/tags/` when stored
741 in Git, so importing the CVS branch symbol `RELENG-1_0-FINAL` would
742 use just `RELENG-1_0-FINAL` for `<name>`, and fast-import will write the
743 corresponding ref as `refs/tags/RELENG-1_0-FINAL`.
744
745 The value of `<name>` must be a valid refname in Git and therefore
746 may contain forward slashes. As `LF` is not valid in a Git refname,
747 no quoting or escaping syntax is supported here.
748
749 The `from` command is the same as in the `commit` command; see
750 above for details.
751
752 The `tagger` command uses the same format as `committer` within
753 `commit`; again see above for details.
754
755 The `data` command following `tagger` must supply the annotated tag
756 message (see below for `data` command syntax). To import an empty
757 tag message use a 0 length data. Tag messages are free-form and are
758 not interpreted by Git. Currently they must be encoded in UTF-8,
759 as fast-import does not permit other encodings to be specified.
760
761 Signing annotated tags during import from within fast-import is not
762 supported. Trying to include your own PGP/GPG signature is not
763 recommended, as the frontend does not (easily) have access to the
764 complete set of bytes which normally goes into such a signature.
765 If signing is required, create lightweight tags from within fast-import with
766 `reset`, then create the annotated versions of those tags offline
767 with the standard 'git tag' process.
768
769 `reset`
770 ~~~~~~~
771 Creates (or recreates) the named branch, optionally starting from
772 a specific revision. The reset command allows a frontend to issue
773 a new `from` command for an existing branch, or to create a new
774 branch from an existing commit without creating a new commit.
775
776 ....
777 'reset' SP <ref> LF
778 ('from' SP <committish> LF)?
779 LF?
780 ....
781
782 For a detailed description of `<ref>` and `<committish>` see above
783 under `commit` and `from`.
784
785 The `LF` after the command is optional (it used to be required).
786
787 The `reset` command can also be used to create lightweight
788 (non-annotated) tags. For example:
789
790 ====
791 reset refs/tags/938
792 from :938
793 ====
794
795 would create the lightweight tag `refs/tags/938` referring to
796 whatever commit mark `:938` references.
797
798 `blob`
799 ~~~~~~
800 Requests writing one file revision to the packfile. The revision
801 is not connected to any commit; this connection must be formed in
802 a subsequent `commit` command by referencing the blob through an
803 assigned mark.
804
805 ....
806 'blob' LF
807 mark?
808 data
809 ....
810
811 The mark command is optional here as some frontends have chosen
812 to generate the Git SHA-1 for the blob on their own, and feed that
813 directly to `commit`. This is typically more work than it's worth
814 however, as marks are inexpensive to store and easy to use.
815
816 `data`
817 ~~~~~~
818 Supplies raw data (for use as blob/file content, commit messages, or
819 annotated tag messages) to fast-import. Data can be supplied using an exact
820 byte count or delimited with a terminating line. Real frontends
821 intended for production-quality conversions should always use the
822 exact byte count format, as it is more robust and performs better.
823 The delimited format is intended primarily for testing fast-import.
824
825 Comment lines appearing within the `<raw>` part of `data` commands
826 are always taken to be part of the body of the data and are therefore
827 never ignored by fast-import. This makes it safe to import any
828 file/message content whose lines might start with `#`.
829
830 Exact byte count format::
831 The frontend must specify the number of bytes of data.
832 +
833 ....
834 'data' SP <count> LF
835 <raw> LF?
836 ....
837 +
838 where `<count>` is the exact number of bytes appearing within
839 `<raw>`. The value of `<count>` is expressed as an ASCII decimal
840 integer. The `LF` on either side of `<raw>` is not
841 included in `<count>` and will not be included in the imported data.
842 +
843 The `LF` after `<raw>` is optional (it used to be required) but
844 recommended. Always including it makes debugging a fast-import
845 stream easier as the next command always starts in column 0
846 of the next line, even if `<raw>` did not end with an `LF`.
847
848 Delimited format::
849 A delimiter string is used to mark the end of the data.
850 fast-import will compute the length by searching for the delimiter.
851 This format is primarily useful for testing and is not
852 recommended for real data.
853 +
854 ....
855 'data' SP '<<' <delim> LF
856 <raw> LF
857 <delim> LF
858 LF?
859 ....
860 +
861 where `<delim>` is the chosen delimiter string. The string `<delim>`
862 must not appear on a line by itself within `<raw>`, as otherwise
863 fast-import will think the data ends earlier than it really does. The `LF`
864 immediately trailing `<raw>` is part of `<raw>`. This is one of
865 the limitations of the delimited format, it is impossible to supply
866 a data chunk which does not have an LF as its last byte.
867 +
868 The `LF` after `<delim> LF` is optional (it used to be required).
869
870 `checkpoint`
871 ~~~~~~~~~~~~
872 Forces fast-import to close the current packfile, start a new one, and to
873 save out all current branch refs, tags and marks.
874
875 ....
876 'checkpoint' LF
877 LF?
878 ....
879
880 Note that fast-import automatically switches packfiles when the current
881 packfile reaches \--max-pack-size, or 4 GiB, whichever limit is
882 smaller. During an automatic packfile switch fast-import does not update
883 the branch refs, tags or marks.
884
885 As a `checkpoint` can require a significant amount of CPU time and
886 disk IO (to compute the overall pack SHA-1 checksum, generate the
887 corresponding index file, and update the refs) it can easily take
888 several minutes for a single `checkpoint` command to complete.
889
890 Frontends may choose to issue checkpoints during extremely large
891 and long running imports, or when they need to allow another Git
892 process access to a branch. However given that a 30 GiB Subversion
893 repository can be loaded into Git through fast-import in about 3 hours,
894 explicit checkpointing may not be necessary.
895
896 The `LF` after the command is optional (it used to be required).
897
898 `progress`
899 ~~~~~~~~~~
900 Causes fast-import to print the entire `progress` line unmodified to
901 its standard output channel (file descriptor 1) when the command is
902 processed from the input stream. The command otherwise has no impact
903 on the current import, or on any of fast-import's internal state.
904
905 ....
906 'progress' SP <any> LF
907 LF?
908 ....
909
910 The `<any>` part of the command may contain any sequence of bytes
911 that does not contain `LF`. The `LF` after the command is optional.
912 Callers may wish to process the output through a tool such as sed to
913 remove the leading part of the line, for example:
914
915 ====
916 frontend | git fast-import | sed 's/^progress //'
917 ====
918
919 Placing a `progress` command immediately after a `checkpoint` will
920 inform the reader when the `checkpoint` has been completed and it
921 can safely access the refs that fast-import updated.
922
923 `cat-blob`
924 ~~~~~~~~~~
925 Causes fast-import to print a blob to a file descriptor previously
926 arranged with the `--cat-blob-fd` argument. The command otherwise
927 has no impact on the current import; its main purpose is to
928 retrieve blobs that may be in fast-import's memory but not
929 accessible from the target repository.
930
931 ....
932 'cat-blob' SP <dataref> LF
933 ....
934
935 The `<dataref>` can be either a mark reference (`:<idnum>`)
936 set previously or a full 40-byte SHA-1 of a Git blob, preexisting or
937 ready to be written.
938
939 Output uses the same format as `git cat-file --batch`:
940
941 ====
942 <sha1> SP 'blob' SP <size> LF
943 <contents> LF
944 ====
945
946 This command can be used anywhere in the stream that comments are
947 accepted. In particular, the `cat-blob` command can be used in the
948 middle of a commit but not in the middle of a `data` command.
949
950 See ``Responses To Commands'' below for details about how to read
951 this output safely.
952
953 `ls`
954 ~~~~
955 Prints information about the object at a path to a file descriptor
956 previously arranged with the `--cat-blob-fd` argument. This allows
957 printing a blob from the active commit (with `cat-blob`) or copying a
958 blob or tree from a previous commit for use in the current one (with
959 `filemodify`).
960
961 The `ls` command can be used anywhere in the stream that comments are
962 accepted, including the middle of a commit.
963
964 Reading from the active commit::
965 This form can only be used in the middle of a `commit`.
966 The path names a directory entry within fast-import's
967 active commit. The path must be quoted in this case.
968 +
969 ....
970 'ls' SP <path> LF
971 ....
972
973 Reading from a named tree::
974 The `<dataref>` can be a mark reference (`:<idnum>`) or the
975 full 40-byte SHA-1 of a Git tag, commit, or tree object,
976 preexisting or waiting to be written.
977 The path is relative to the top level of the tree
978 named by `<dataref>`.
979 +
980 ....
981 'ls' SP <dataref> SP <path> LF
982 ....
983
984 See `filemodify` above for a detailed description of `<path>`.
985
986 Output uses the same format as `git ls-tree <tree> -- <path>`:
987
988 ====
989 <mode> SP ('blob' | 'tree' | 'commit') SP <dataref> HT <path> LF
990 ====
991
992 The <dataref> represents the blob, tree, or commit object at <path>
993 and can be used in later 'cat-blob', 'filemodify', or 'ls' commands.
994
995 If there is no file or subtree at that path, 'git fast-import' will
996 instead report
997
998 ====
999 missing SP <path> LF
1000 ====
1001
1002 See ``Responses To Commands'' below for details about how to read
1003 this output safely.
1004
1005 `feature`
1006 ~~~~~~~~~
1007 Require that fast-import supports the specified feature, or abort if
1008 it does not.
1009
1010 ....
1011 'feature' SP <feature> ('=' <argument>)? LF
1012 ....
1013
1014 The <feature> part of the command may be any one of the following:
1015
1016 date-format::
1017 export-marks::
1018 relative-marks::
1019 no-relative-marks::
1020 force::
1021 Act as though the corresponding command-line option with
1022 a leading '--' was passed on the command line
1023 (see OPTIONS, above).
1024
1025 import-marks::
1026 import-marks-if-exists::
1027 Like --import-marks except in two respects: first, only one
1028 "feature import-marks" or "feature import-marks-if-exists"
1029 command is allowed per stream; second, an --import-marks=
1030 or --import-marks-if-exists command-line option overrides
1031 any of these "feature" commands in the stream; third,
1032 "feature import-marks-if-exists" like a corresponding
1033 command-line option silently skips a nonexistent file.
1034
1035 cat-blob::
1036 ls::
1037 Require that the backend support the 'cat-blob' or 'ls' command.
1038 Versions of fast-import not supporting the specified command
1039 will exit with a message indicating so.
1040 This lets the import error out early with a clear message,
1041 rather than wasting time on the early part of an import
1042 before the unsupported command is detected.
1043
1044 notes::
1045 Require that the backend support the 'notemodify' (N)
1046 subcommand to the 'commit' command.
1047 Versions of fast-import not supporting notes will exit
1048 with a message indicating so.
1049
1050 done::
1051 Error out if the stream ends without a 'done' command.
1052 Without this feature, errors causing the frontend to end
1053 abruptly at a convenient point in the stream can go
1054 undetected. This may occur, for example, if an import
1055 front end dies in mid-operation without emitting SIGTERM
1056 or SIGKILL at its subordinate git fast-import instance.
1057
1058 `option`
1059 ~~~~~~~~
1060 Processes the specified option so that git fast-import behaves in a
1061 way that suits the frontend's needs.
1062 Note that options specified by the frontend are overridden by any
1063 options the user may specify to git fast-import itself.
1064
1065 ....
1066 'option' SP <option> LF
1067 ....
1068
1069 The `<option>` part of the command may contain any of the options
1070 listed in the OPTIONS section that do not change import semantics,
1071 without the leading '--' and is treated in the same way.
1072
1073 Option commands must be the first commands on the input (not counting
1074 feature commands), to give an option command after any non-option
1075 command is an error.
1076
1077 The following commandline options change import semantics and may therefore
1078 not be passed as option:
1079
1080 * date-format
1081 * import-marks
1082 * export-marks
1083 * cat-blob-fd
1084 * force
1085
1086 `done`
1087 ~~~~~~
1088 If the `done` feature is not in use, treated as if EOF was read.
1089 This can be used to tell fast-import to finish early.
1090
1091 If the `--done` command line option or `feature done` command is
1092 in use, the `done` command is mandatory and marks the end of the
1093 stream.
1094
1095 Responses To Commands
1096 ---------------------
1097 New objects written by fast-import are not available immediately.
1098 Most fast-import commands have no visible effect until the next
1099 checkpoint (or completion). The frontend can send commands to
1100 fill fast-import's input pipe without worrying about how quickly
1101 they will take effect, which improves performance by simplifying
1102 scheduling.
1103
1104 For some frontends, though, it is useful to be able to read back
1105 data from the current repository as it is being updated (for
1106 example when the source material describes objects in terms of
1107 patches to be applied to previously imported objects). This can
1108 be accomplished by connecting the frontend and fast-import via
1109 bidirectional pipes:
1110
1111 ====
1112 mkfifo fast-import-output
1113 frontend <fast-import-output |
1114 git fast-import >fast-import-output
1115 ====
1116
1117 A frontend set up this way can use `progress`, `ls`, and `cat-blob`
1118 commands to read information from the import in progress.
1119
1120 To avoid deadlock, such frontends must completely consume any
1121 pending output from `progress`, `ls`, and `cat-blob` before
1122 performing writes to fast-import that might block.
1123
1124 Crash Reports
1125 -------------
1126 If fast-import is supplied invalid input it will terminate with a
1127 non-zero exit status and create a crash report in the top level of
1128 the Git repository it was importing into. Crash reports contain
1129 a snapshot of the internal fast-import state as well as the most
1130 recent commands that lead up to the crash.
1131
1132 All recent commands (including stream comments, file changes and
1133 progress commands) are shown in the command history within the crash
1134 report, but raw file data and commit messages are excluded from the
1135 crash report. This exclusion saves space within the report file
1136 and reduces the amount of buffering that fast-import must perform
1137 during execution.
1138
1139 After writing a crash report fast-import will close the current
1140 packfile and export the marks table. This allows the frontend
1141 developer to inspect the repository state and resume the import from
1142 the point where it crashed. The modified branches and tags are not
1143 updated during a crash, as the import did not complete successfully.
1144 Branch and tag information can be found in the crash report and
1145 must be applied manually if the update is needed.
1146
1147 An example crash:
1148
1149 ====
1150 $ cat >in <<END_OF_INPUT
1151 # my very first test commit
1152 commit refs/heads/master
1153 committer Shawn O. Pearce <spearce> 19283 -0400
1154 # who is that guy anyway?
1155 data <<EOF
1156 this is my commit
1157 EOF
1158 M 644 inline .gitignore
1159 data <<EOF
1160 .gitignore
1161 EOF
1162 M 777 inline bob
1163 END_OF_INPUT
1164
1165 $ git fast-import <in
1166 fatal: Corrupt mode: M 777 inline bob
1167 fast-import: dumping crash report to .git/fast_import_crash_8434
1168
1169 $ cat .git/fast_import_crash_8434
1170 fast-import crash report:
1171 fast-import process: 8434
1172 parent process : 1391
1173 at Sat Sep 1 00:58:12 2007
1174
1175 fatal: Corrupt mode: M 777 inline bob
1176
1177 Most Recent Commands Before Crash
1178 ---------------------------------
1179 # my very first test commit
1180 commit refs/heads/master
1181 committer Shawn O. Pearce <spearce> 19283 -0400
1182 # who is that guy anyway?
1183 data <<EOF
1184 M 644 inline .gitignore
1185 data <<EOF
1186 * M 777 inline bob
1187
1188 Active Branch LRU
1189 -----------------
1190 active_branches = 1 cur, 5 max
1191
1192 pos clock name
1193 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1194 1) 0 refs/heads/master
1195
1196 Inactive Branches
1197 -----------------
1198 refs/heads/master:
1199 status : active loaded dirty
1200 tip commit : 0000000000000000000000000000000000000000
1201 old tree : 0000000000000000000000000000000000000000
1202 cur tree : 0000000000000000000000000000000000000000
1203 commit clock: 0
1204 last pack :
1205
1206
1207 -------------------
1208 END OF CRASH REPORT
1209 ====
1210
1211 Tips and Tricks
1212 ---------------
1213 The following tips and tricks have been collected from various
1214 users of fast-import, and are offered here as suggestions.
1215
1216 Use One Mark Per Commit
1217 ~~~~~~~~~~~~~~~~~~~~~~~
1218 When doing a repository conversion, use a unique mark per commit
1219 (`mark :<n>`) and supply the \--export-marks option on the command
1220 line. fast-import will dump a file which lists every mark and the Git
1221 object SHA-1 that corresponds to it. If the frontend can tie
1222 the marks back to the source repository, it is easy to verify the
1223 accuracy and completeness of the import by comparing each Git
1224 commit to the corresponding source revision.
1225
1226 Coming from a system such as Perforce or Subversion this should be
1227 quite simple, as the fast-import mark can also be the Perforce changeset
1228 number or the Subversion revision number.
1229
1230 Freely Skip Around Branches
1231 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
1232 Don't bother trying to optimize the frontend to stick to one branch
1233 at a time during an import. Although doing so might be slightly
1234 faster for fast-import, it tends to increase the complexity of the frontend
1235 code considerably.
1236
1237 The branch LRU builtin to fast-import tends to behave very well, and the
1238 cost of activating an inactive branch is so low that bouncing around
1239 between branches has virtually no impact on import performance.
1240
1241 Handling Renames
1242 ~~~~~~~~~~~~~~~~
1243 When importing a renamed file or directory, simply delete the old
1244 name(s) and modify the new name(s) during the corresponding commit.
1245 Git performs rename detection after-the-fact, rather than explicitly
1246 during a commit.
1247
1248 Use Tag Fixup Branches
1249 ~~~~~~~~~~~~~~~~~~~~~~
1250 Some other SCM systems let the user create a tag from multiple
1251 files which are not from the same commit/changeset. Or to create
1252 tags which are a subset of the files available in the repository.
1253
1254 Importing these tags as-is in Git is impossible without making at
1255 least one commit which ``fixes up'' the files to match the content
1256 of the tag. Use fast-import's `reset` command to reset a dummy branch
1257 outside of your normal branch space to the base commit for the tag,
1258 then commit one or more file fixup commits, and finally tag the
1259 dummy branch.
1260
1261 For example since all normal branches are stored under `refs/heads/`
1262 name the tag fixup branch `TAG_FIXUP`. This way it is impossible for
1263 the fixup branch used by the importer to have namespace conflicts
1264 with real branches imported from the source (the name `TAG_FIXUP`
1265 is not `refs/heads/TAG_FIXUP`).
1266
1267 When committing fixups, consider using `merge` to connect the
1268 commit(s) which are supplying file revisions to the fixup branch.
1269 Doing so will allow tools such as 'git blame' to track
1270 through the real commit history and properly annotate the source
1271 files.
1272
1273 After fast-import terminates the frontend will need to do `rm .git/TAG_FIXUP`
1274 to remove the dummy branch.
1275
1276 Import Now, Repack Later
1277 ~~~~~~~~~~~~~~~~~~~~~~~~
1278 As soon as fast-import completes the Git repository is completely valid
1279 and ready for use. Typically this takes only a very short time,
1280 even for considerably large projects (100,000+ commits).
1281
1282 However repacking the repository is necessary to improve data
1283 locality and access performance. It can also take hours on extremely
1284 large projects (especially if -f and a large \--window parameter is
1285 used). Since repacking is safe to run alongside readers and writers,
1286 run the repack in the background and let it finish when it finishes.
1287 There is no reason to wait to explore your new Git project!
1288
1289 If you choose to wait for the repack, don't try to run benchmarks
1290 or performance tests until repacking is completed. fast-import outputs
1291 suboptimal packfiles that are simply never seen in real use
1292 situations.
1293
1294 Repacking Historical Data
1295 ~~~~~~~~~~~~~~~~~~~~~~~~~
1296 If you are repacking very old imported data (e.g. older than the
1297 last year), consider expending some extra CPU time and supplying
1298 \--window=50 (or higher) when you run 'git repack'.
1299 This will take longer, but will also produce a smaller packfile.
1300 You only need to expend the effort once, and everyone using your
1301 project will benefit from the smaller repository.
1302
1303 Include Some Progress Messages
1304 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1305 Every once in a while have your frontend emit a `progress` message
1306 to fast-import. The contents of the messages are entirely free-form,
1307 so one suggestion would be to output the current month and year
1308 each time the current commit date moves into the next month.
1309 Your users will feel better knowing how much of the data stream
1310 has been processed.
1311
1312
1313 Packfile Optimization
1314 ---------------------
1315 When packing a blob fast-import always attempts to deltify against the last
1316 blob written. Unless specifically arranged for by the frontend,
1317 this will probably not be a prior version of the same file, so the
1318 generated delta will not be the smallest possible. The resulting
1319 packfile will be compressed, but will not be optimal.
1320
1321 Frontends which have efficient access to all revisions of a
1322 single file (for example reading an RCS/CVS ,v file) can choose
1323 to supply all revisions of that file as a sequence of consecutive
1324 `blob` commands. This allows fast-import to deltify the different file
1325 revisions against each other, saving space in the final packfile.
1326 Marks can be used to later identify individual file revisions during
1327 a sequence of `commit` commands.
1328
1329 The packfile(s) created by fast-import do not encourage good disk access
1330 patterns. This is caused by fast-import writing the data in the order
1331 it is received on standard input, while Git typically organizes
1332 data within packfiles to make the most recent (current tip) data
1333 appear before historical data. Git also clusters commits together,
1334 speeding up revision traversal through better cache locality.
1335
1336 For this reason it is strongly recommended that users repack the
1337 repository with `git repack -a -d` after fast-import completes, allowing
1338 Git to reorganize the packfiles for faster data access. If blob
1339 deltas are suboptimal (see above) then also adding the `-f` option
1340 to force recomputation of all deltas can significantly reduce the
1341 final packfile size (30-50% smaller can be quite typical).
1342
1343
1344 Memory Utilization
1345 ------------------
1346 There are a number of factors which affect how much memory fast-import
1347 requires to perform an import. Like critical sections of core
1348 Git, fast-import uses its own memory allocators to amortize any overheads
1349 associated with malloc. In practice fast-import tends to amortize any
1350 malloc overheads to 0, due to its use of large block allocations.
1351
1352 per object
1353 ~~~~~~~~~~
1354 fast-import maintains an in-memory structure for every object written in
1355 this execution. On a 32 bit system the structure is 32 bytes,
1356 on a 64 bit system the structure is 40 bytes (due to the larger
1357 pointer sizes). Objects in the table are not deallocated until
1358 fast-import terminates. Importing 2 million objects on a 32 bit system
1359 will require approximately 64 MiB of memory.
1360
1361 The object table is actually a hashtable keyed on the object name
1362 (the unique SHA-1). This storage configuration allows fast-import to reuse
1363 an existing or already written object and avoid writing duplicates
1364 to the output packfile. Duplicate blobs are surprisingly common
1365 in an import, typically due to branch merges in the source.
1366
1367 per mark
1368 ~~~~~~~~
1369 Marks are stored in a sparse array, using 1 pointer (4 bytes or 8
1370 bytes, depending on pointer size) per mark. Although the array
1371 is sparse, frontends are still strongly encouraged to use marks
1372 between 1 and n, where n is the total number of marks required for
1373 this import.
1374
1375 per branch
1376 ~~~~~~~~~~
1377 Branches are classified as active and inactive. The memory usage
1378 of the two classes is significantly different.
1379
1380 Inactive branches are stored in a structure which uses 96 or 120
1381 bytes (32 bit or 64 bit systems, respectively), plus the length of
1382 the branch name (typically under 200 bytes), per branch. fast-import will
1383 easily handle as many as 10,000 inactive branches in under 2 MiB
1384 of memory.
1385
1386 Active branches have the same overhead as inactive branches, but
1387 also contain copies of every tree that has been recently modified on
1388 that branch. If subtree `include` has not been modified since the
1389 branch became active, its contents will not be loaded into memory,
1390 but if subtree `src` has been modified by a commit since the branch
1391 became active, then its contents will be loaded in memory.
1392
1393 As active branches store metadata about the files contained on that
1394 branch, their in-memory storage size can grow to a considerable size
1395 (see below).
1396
1397 fast-import automatically moves active branches to inactive status based on
1398 a simple least-recently-used algorithm. The LRU chain is updated on
1399 each `commit` command. The maximum number of active branches can be
1400 increased or decreased on the command line with \--active-branches=.
1401
1402 per active tree
1403 ~~~~~~~~~~~~~~~
1404 Trees (aka directories) use just 12 bytes of memory on top of the
1405 memory required for their entries (see ``per active file'' below).
1406 The cost of a tree is virtually 0, as its overhead amortizes out
1407 over the individual file entries.
1408
1409 per active file entry
1410 ~~~~~~~~~~~~~~~~~~~~~
1411 Files (and pointers to subtrees) within active trees require 52 or 64
1412 bytes (32/64 bit platforms) per entry. To conserve space, file and
1413 tree names are pooled in a common string table, allowing the filename
1414 ``Makefile'' to use just 16 bytes (after including the string header
1415 overhead) no matter how many times it occurs within the project.
1416
1417 The active branch LRU, when coupled with the filename string pool
1418 and lazy loading of subtrees, allows fast-import to efficiently import
1419 projects with 2,000+ branches and 45,114+ files in a very limited
1420 memory footprint (less than 2.7 MiB per active branch).
1421
1422 Signals
1423 -------
1424 Sending *SIGUSR1* to the 'git fast-import' process ends the current
1425 packfile early, simulating a `checkpoint` command. The impatient
1426 operator can use this facility to peek at the objects and refs from an
1427 import in progress, at the cost of some added running time and worse
1428 compression.
1429
1430 GIT
1431 ---
1432 Part of the linkgit:git[1] suite