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1 | git-fast-import(1) |
2 | ================== | |
3 | ||
4 | NAME | |
5 | ---- | |
7a33631f | 6 | git-fast-import - Backend for fast Git data importers |
6e411d20 SP |
7 | |
8 | ||
9 | SYNOPSIS | |
10 | -------- | |
b1889c36 | 11 | frontend | 'git fast-import' [options] |
6e411d20 SP |
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 | |
ba020ef5 | 18 | stored there to 'git-fast-import'. |
6e411d20 | 19 | |
882227f1 | 20 | fast-import reads a mixed command/data stream from standard input and |
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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 | ||
882227f1 | 26 | The fast-import backend itself can import into an empty repository (one that |
ba020ef5 | 27 | has already been initialized by 'git-init') or incrementally |
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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 | ------- | |
63e0c8b3 SP |
35 | --date-format=<fmt>:: |
36 | Specify the type of dates the frontend will supply to | |
882227f1 | 37 | fast-import within `author`, `committer` and `tagger` commands. |
63e0c8b3 SP |
38 | See ``Date Formats'' below for details about which formats |
39 | are supported, and their syntax. | |
40 | ||
7073e69e SP |
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 | ||
6e411d20 SP |
46 | --max-pack-size=<n>:: |
47 | Maximum size of each output packfile, expressed in MiB. | |
48 | The default is 4096 (4 GiB) as that is the maximum allowed | |
49 | packfile size (due to file format limitations). Some | |
50 | importers may wish to lower this, such as to ensure the | |
51 | resulting packfiles fit on CDs. | |
52 | ||
53 | --depth=<n>:: | |
54 | Maximum delta depth, for blob and tree deltification. | |
55 | Default is 10. | |
56 | ||
57 | --active-branches=<n>:: | |
58 | Maximum number of branches to maintain active at once. | |
59 | See ``Memory Utilization'' below for details. Default is 5. | |
60 | ||
61 | --export-marks=<file>:: | |
62 | Dumps the internal marks table to <file> when complete. | |
63 | Marks are written one per line as `:markid SHA-1`. | |
64 | Frontends can use this file to validate imports after they | |
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65 | have been completed, or to save the marks table across |
66 | incremental runs. As <file> is only opened and truncated | |
67 | at checkpoint (or completion) the same path can also be | |
68 | safely given to \--import-marks. | |
69 | ||
70 | --import-marks=<file>:: | |
71 | Before processing any input, load the marks specified in | |
72 | <file>. The input file must exist, must be readable, and | |
73 | must use the same format as produced by \--export-marks. | |
74 | Multiple options may be supplied to import more than one | |
75 | set of marks. If a mark is defined to different values, | |
76 | the last file wins. | |
6e411d20 | 77 | |
bdf1c06d SP |
78 | --export-pack-edges=<file>:: |
79 | After creating a packfile, print a line of data to | |
80 | <file> listing the filename of the packfile and the last | |
81 | commit on each branch that was written to that packfile. | |
82 | This information may be useful after importing projects | |
83 | whose total object set exceeds the 4 GiB packfile limit, | |
84 | as these commits can be used as edge points during calls | |
ba020ef5 | 85 | to 'git-pack-objects'. |
bdf1c06d | 86 | |
c499d768 | 87 | --quiet:: |
882227f1 | 88 | Disable all non-fatal output, making fast-import silent when it |
7f9d77f2 | 89 | is successful. This option disables the output shown by |
c499d768 SP |
90 | \--stats. |
91 | ||
92 | --stats:: | |
882227f1 | 93 | Display some basic statistics about the objects fast-import has |
c499d768 | 94 | created, the packfiles they were stored into, and the |
882227f1 | 95 | memory used by fast-import during this run. Showing this output |
c499d768 SP |
96 | is currently the default, but can be disabled with \--quiet. |
97 | ||
98 | ||
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99 | Performance |
100 | ----------- | |
882227f1 | 101 | The design of fast-import allows it to import large projects in a minimum |
6e411d20 | 102 | amount of memory usage and processing time. Assuming the frontend |
882227f1 | 103 | is able to keep up with fast-import and feed it a constant stream of data, |
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104 | import times for projects holding 10+ years of history and containing |
105 | 100,000+ individual commits are generally completed in just 1-2 | |
106 | hours on quite modest (~$2,000 USD) hardware. | |
107 | ||
108 | Most bottlenecks appear to be in foreign source data access (the | |
882227f1 | 109 | source just cannot extract revisions fast enough) or disk IO (fast-import |
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110 | writes as fast as the disk will take the data). Imports will run |
111 | faster if the source data is stored on a different drive than the | |
112 | destination Git repository (due to less IO contention). | |
113 | ||
114 | ||
115 | Development Cost | |
116 | ---------------- | |
882227f1 | 117 | A typical frontend for fast-import tends to weigh in at approximately 200 |
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118 | lines of Perl/Python/Ruby code. Most developers have been able to |
119 | create working importers in just a couple of hours, even though it | |
882227f1 | 120 | is their first exposure to fast-import, and sometimes even to Git. This is |
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121 | an ideal situation, given that most conversion tools are throw-away |
122 | (use once, and never look back). | |
123 | ||
124 | ||
125 | Parallel Operation | |
126 | ------------------ | |
ba020ef5 | 127 | Like 'git-push' or 'git-fetch', imports handled by fast-import are safe to |
6e411d20 | 128 | run alongside parallel `git repack -a -d` or `git gc` invocations, |
ba020ef5 | 129 | or any other Git operation (including 'git-prune', as loose objects |
882227f1 | 130 | are never used by fast-import). |
6e411d20 | 131 | |
882227f1 SP |
132 | fast-import does not lock the branch or tag refs it is actively importing. |
133 | After the import, during its ref update phase, fast-import tests each | |
7073e69e SP |
134 | existing branch ref to verify the update will be a fast-forward |
135 | update (the commit stored in the ref is contained in the new | |
136 | history of the commit to be written). If the update is not a | |
882227f1 SP |
137 | fast-forward update, fast-import will skip updating that ref and instead |
138 | prints a warning message. fast-import will always attempt to update all | |
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139 | branch refs, and does not stop on the first failure. |
140 | ||
c499d768 SP |
141 | Branch updates can be forced with \--force, but its recommended that |
142 | this only be used on an otherwise quiet repository. Using \--force | |
7073e69e | 143 | is not necessary for an initial import into an empty repository. |
6e411d20 SP |
144 | |
145 | ||
146 | Technical Discussion | |
147 | -------------------- | |
882227f1 | 148 | fast-import tracks a set of branches in memory. Any branch can be created |
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149 | or modified at any point during the import process by sending a |
150 | `commit` command on the input stream. This design allows a frontend | |
151 | program to process an unlimited number of branches simultaneously, | |
152 | generating commits in the order they are available from the source | |
153 | data. It also simplifies the frontend programs considerably. | |
154 | ||
882227f1 | 155 | fast-import does not use or alter the current working directory, or any |
6e411d20 SP |
156 | file within it. (It does however update the current Git repository, |
157 | as referenced by `GIT_DIR`.) Therefore an import frontend may use | |
158 | the working directory for its own purposes, such as extracting file | |
159 | revisions from the foreign source. This ignorance of the working | |
882227f1 | 160 | directory also allows fast-import to run very quickly, as it does not |
6e411d20 SP |
161 | need to perform any costly file update operations when switching |
162 | between branches. | |
163 | ||
164 | Input Format | |
165 | ------------ | |
166 | With the exception of raw file data (which Git does not interpret) | |
882227f1 | 167 | the fast-import input format is text (ASCII) based. This text based |
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168 | format simplifies development and debugging of frontend programs, |
169 | especially when a higher level language such as Perl, Python or | |
170 | Ruby is being used. | |
171 | ||
882227f1 | 172 | fast-import is very strict about its input. Where we say SP below we mean |
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173 | *exactly* one space. Likewise LF means one (and only one) linefeed. |
174 | Supplying additional whitespace characters will cause unexpected | |
175 | results, such as branch names or file names with leading or trailing | |
882227f1 | 176 | spaces in their name, or early termination of fast-import when it encounters |
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177 | unexpected input. |
178 | ||
401d53fa SP |
179 | Stream Comments |
180 | ~~~~~~~~~~~~~~~ | |
181 | To aid in debugging frontends fast-import ignores any line that | |
182 | begins with `#` (ASCII pound/hash) up to and including the line | |
183 | ending `LF`. A comment line may contain any sequence of bytes | |
184 | that does not contain an LF and therefore may be used to include | |
185 | any detailed debugging information that might be specific to the | |
186 | frontend and useful when inspecting a fast-import data stream. | |
187 | ||
63e0c8b3 SP |
188 | Date Formats |
189 | ~~~~~~~~~~~~ | |
190 | The following date formats are supported. A frontend should select | |
191 | the format it will use for this import by passing the format name | |
c499d768 | 192 | in the \--date-format=<fmt> command line option. |
63e0c8b3 SP |
193 | |
194 | `raw`:: | |
9b92c82f | 195 | This is the Git native format and is `<time> SP <offutc>`. |
882227f1 | 196 | It is also fast-import's default format, if \--date-format was |
63e0c8b3 SP |
197 | not specified. |
198 | + | |
199 | The time of the event is specified by `<time>` as the number of | |
200 | seconds since the UNIX epoch (midnight, Jan 1, 1970, UTC) and is | |
201 | written as an ASCII decimal integer. | |
202 | + | |
9b92c82f SP |
203 | The local offset is specified by `<offutc>` as a positive or negative |
204 | offset from UTC. For example EST (which is 5 hours behind UTC) | |
205 | would be expressed in `<tz>` by ``-0500'' while UTC is ``+0000''. | |
206 | The local offset does not affect `<time>`; it is used only as an | |
207 | advisement to help formatting routines display the timestamp. | |
63e0c8b3 | 208 | + |
9b92c82f SP |
209 | If the local offset is not available in the source material, use |
210 | ``+0000'', or the most common local offset. For example many | |
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211 | organizations have a CVS repository which has only ever been accessed |
212 | by users who are located in the same location and timezone. In this | |
f842fdb0 | 213 | case a reasonable offset from UTC could be assumed. |
63e0c8b3 SP |
214 | + |
215 | Unlike the `rfc2822` format, this format is very strict. Any | |
882227f1 | 216 | variation in formatting will cause fast-import to reject the value. |
63e0c8b3 SP |
217 | |
218 | `rfc2822`:: | |
219 | This is the standard email format as described by RFC 2822. | |
220 | + | |
221 | An example value is ``Tue Feb 6 11:22:18 2007 -0500''. The Git | |
f842fdb0 | 222 | parser is accurate, but a little on the lenient side. It is the |
ba020ef5 | 223 | same parser used by 'git-am' when applying patches |
63e0c8b3 SP |
224 | received from email. |
225 | + | |
226 | Some malformed strings may be accepted as valid dates. In some of | |
227 | these cases Git will still be able to obtain the correct date from | |
228 | the malformed string. There are also some types of malformed | |
229 | strings which Git will parse wrong, and yet consider valid. | |
230 | Seriously malformed strings will be rejected. | |
231 | + | |
9b92c82f SP |
232 | Unlike the `raw` format above, the timezone/UTC offset information |
233 | contained in an RFC 2822 date string is used to adjust the date | |
234 | value to UTC prior to storage. Therefore it is important that | |
235 | this information be as accurate as possible. | |
236 | + | |
f842fdb0 | 237 | If the source material uses RFC 2822 style dates, |
882227f1 | 238 | the frontend should let fast-import handle the parsing and conversion |
63e0c8b3 SP |
239 | (rather than attempting to do it itself) as the Git parser has |
240 | been well tested in the wild. | |
241 | + | |
242 | Frontends should prefer the `raw` format if the source material | |
f842fdb0 | 243 | already uses UNIX-epoch format, can be coaxed to give dates in that |
02783075 | 244 | format, or its format is easily convertible to it, as there is no |
f842fdb0 | 245 | ambiguity in parsing. |
63e0c8b3 SP |
246 | |
247 | `now`:: | |
248 | Always use the current time and timezone. The literal | |
249 | `now` must always be supplied for `<when>`. | |
250 | + | |
251 | This is a toy format. The current time and timezone of this system | |
252 | is always copied into the identity string at the time it is being | |
882227f1 | 253 | created by fast-import. There is no way to specify a different time or |
63e0c8b3 SP |
254 | timezone. |
255 | + | |
256 | This particular format is supplied as its short to implement and | |
257 | may be useful to a process that wants to create a new commit | |
258 | right now, without needing to use a working directory or | |
ba020ef5 | 259 | 'git-update-index'. |
63e0c8b3 SP |
260 | + |
261 | If separate `author` and `committer` commands are used in a `commit` | |
262 | the timestamps may not match, as the system clock will be polled | |
263 | twice (once for each command). The only way to ensure that both | |
264 | author and committer identity information has the same timestamp | |
265 | is to omit `author` (thus copying from `committer`) or to use a | |
266 | date format other than `now`. | |
267 | ||
6e411d20 SP |
268 | Commands |
269 | ~~~~~~~~ | |
882227f1 | 270 | fast-import accepts several commands to update the current repository |
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271 | and control the current import process. More detailed discussion |
272 | (with examples) of each command follows later. | |
273 | ||
274 | `commit`:: | |
275 | Creates a new branch or updates an existing branch by | |
276 | creating a new commit and updating the branch to point at | |
277 | the newly created commit. | |
278 | ||
279 | `tag`:: | |
280 | Creates an annotated tag object from an existing commit or | |
281 | branch. Lightweight tags are not supported by this command, | |
282 | as they are not recommended for recording meaningful points | |
283 | in time. | |
284 | ||
285 | `reset`:: | |
286 | Reset an existing branch (or a new branch) to a specific | |
287 | revision. This command must be used to change a branch to | |
288 | a specific revision without making a commit on it. | |
289 | ||
290 | `blob`:: | |
291 | Convert raw file data into a blob, for future use in a | |
292 | `commit` command. This command is optional and is not | |
293 | needed to perform an import. | |
294 | ||
295 | `checkpoint`:: | |
882227f1 | 296 | Forces fast-import to close the current packfile, generate its |
6e411d20 SP |
297 | unique SHA-1 checksum and index, and start a new packfile. |
298 | This command is optional and is not needed to perform | |
299 | an import. | |
300 | ||
ac053c02 SP |
301 | `progress`:: |
302 | Causes fast-import to echo the entire line to its own | |
303 | standard output. This command is optional and is not needed | |
304 | to perform an import. | |
305 | ||
6e411d20 SP |
306 | `commit` |
307 | ~~~~~~~~ | |
308 | Create or update a branch with a new commit, recording one logical | |
309 | change to the project. | |
310 | ||
311 | .... | |
312 | 'commit' SP <ref> LF | |
313 | mark? | |
63e0c8b3 SP |
314 | ('author' SP <name> SP LT <email> GT SP <when> LF)? |
315 | 'committer' SP <name> SP LT <email> GT SP <when> LF | |
6e411d20 SP |
316 | data |
317 | ('from' SP <committish> LF)? | |
318 | ('merge' SP <committish> LF)? | |
b6f3481b | 319 | (filemodify | filedelete | filecopy | filerename | filedeleteall)* |
1fdb649c | 320 | LF? |
6e411d20 SP |
321 | .... |
322 | ||
323 | where `<ref>` is the name of the branch to make the commit on. | |
324 | Typically branch names are prefixed with `refs/heads/` in | |
325 | Git, so importing the CVS branch symbol `RELENG-1_0` would use | |
326 | `refs/heads/RELENG-1_0` for the value of `<ref>`. The value of | |
327 | `<ref>` must be a valid refname in Git. As `LF` is not valid in | |
328 | a Git refname, no quoting or escaping syntax is supported here. | |
329 | ||
882227f1 | 330 | A `mark` command may optionally appear, requesting fast-import to save a |
6e411d20 SP |
331 | reference to the newly created commit for future use by the frontend |
332 | (see below for format). It is very common for frontends to mark | |
333 | every commit they create, thereby allowing future branch creation | |
334 | from any imported commit. | |
335 | ||
336 | The `data` command following `committer` must supply the commit | |
337 | message (see below for `data` command syntax). To import an empty | |
338 | commit message use a 0 length data. Commit messages are free-form | |
339 | and are not interpreted by Git. Currently they must be encoded in | |
882227f1 | 340 | UTF-8, as fast-import does not permit other encodings to be specified. |
6e411d20 | 341 | |
b6f3481b SP |
342 | Zero or more `filemodify`, `filedelete`, `filecopy`, `filerename` |
343 | and `filedeleteall` commands | |
825769a8 SP |
344 | may be included to update the contents of the branch prior to |
345 | creating the commit. These commands may be supplied in any order. | |
02783075 | 346 | However it is recommended that a `filedeleteall` command precede |
b6f3481b SP |
347 | all `filemodify`, `filecopy` and `filerename` commands in the same |
348 | commit, as `filedeleteall` | |
825769a8 | 349 | wipes the branch clean (see below). |
6e411d20 | 350 | |
1fdb649c SP |
351 | The `LF` after the command is optional (it used to be required). |
352 | ||
6e411d20 SP |
353 | `author` |
354 | ^^^^^^^^ | |
355 | An `author` command may optionally appear, if the author information | |
356 | might differ from the committer information. If `author` is omitted | |
882227f1 | 357 | then fast-import will automatically use the committer's information for |
6e411d20 SP |
358 | the author portion of the commit. See below for a description of |
359 | the fields in `author`, as they are identical to `committer`. | |
360 | ||
361 | `committer` | |
362 | ^^^^^^^^^^^ | |
363 | The `committer` command indicates who made this commit, and when | |
364 | they made it. | |
365 | ||
366 | Here `<name>` is the person's display name (for example | |
367 | ``Com M Itter'') and `<email>` is the person's email address | |
368 | (``cm@example.com''). `LT` and `GT` are the literal less-than (\x3c) | |
369 | and greater-than (\x3e) symbols. These are required to delimit | |
370 | the email address from the other fields in the line. Note that | |
371 | `<name>` is free-form and may contain any sequence of bytes, except | |
372 | `LT` and `LF`. It is typically UTF-8 encoded. | |
373 | ||
63e0c8b3 | 374 | The time of the change is specified by `<when>` using the date format |
c499d768 | 375 | that was selected by the \--date-format=<fmt> command line option. |
63e0c8b3 SP |
376 | See ``Date Formats'' above for the set of supported formats, and |
377 | their syntax. | |
6e411d20 SP |
378 | |
379 | `from` | |
380 | ^^^^^^ | |
ea5e370a SP |
381 | The `from` command is used to specify the commit to initialize |
382 | this branch from. This revision will be the first ancestor of the | |
383 | new commit. | |
384 | ||
385 | Omitting the `from` command in the first commit of a new branch | |
386 | will cause fast-import to create that commit with no ancestor. This | |
387 | tends to be desired only for the initial commit of a project. | |
9b33fa08 EB |
388 | If the frontend creates all files from scratch when making a new |
389 | branch, a `merge` command may be used instead of `from` to start | |
390 | the commit with an empty tree. | |
ea5e370a SP |
391 | Omitting the `from` command on existing branches is usually desired, |
392 | as the current commit on that branch is automatically assumed to | |
393 | be the first ancestor of the new commit. | |
6e411d20 SP |
394 | |
395 | As `LF` is not valid in a Git refname or SHA-1 expression, no | |
396 | quoting or escaping syntax is supported within `<committish>`. | |
397 | ||
398 | Here `<committish>` is any of the following: | |
399 | ||
882227f1 SP |
400 | * The name of an existing branch already in fast-import's internal branch |
401 | table. If fast-import doesn't know the name, its treated as a SHA-1 | |
6e411d20 SP |
402 | expression. |
403 | ||
404 | * A mark reference, `:<idnum>`, where `<idnum>` is the mark number. | |
405 | + | |
882227f1 | 406 | The reason fast-import uses `:` to denote a mark reference is this character |
6e411d20 | 407 | is not legal in a Git branch name. The leading `:` makes it easy |
02783075 | 408 | to distinguish between the mark 42 (`:42`) and the branch 42 (`42` |
6e411d20 SP |
409 | or `refs/heads/42`), or an abbreviated SHA-1 which happened to |
410 | consist only of base-10 digits. | |
411 | + | |
412 | Marks must be declared (via `mark`) before they can be used. | |
413 | ||
414 | * A complete 40 byte or abbreviated commit SHA-1 in hex. | |
415 | ||
416 | * Any valid Git SHA-1 expression that resolves to a commit. See | |
5162e697 | 417 | ``SPECIFYING REVISIONS'' in linkgit:git-rev-parse[1] for details. |
6e411d20 SP |
418 | |
419 | The special case of restarting an incremental import from the | |
420 | current branch value should be written as: | |
421 | ---- | |
422 | from refs/heads/branch^0 | |
423 | ---- | |
882227f1 | 424 | The `{caret}0` suffix is necessary as fast-import does not permit a branch to |
6e411d20 | 425 | start from itself, and the branch is created in memory before the |
209f1298 | 426 | `from` command is even read from the input. Adding `{caret}0` will force |
882227f1 | 427 | fast-import to resolve the commit through Git's revision parsing library, |
6e411d20 SP |
428 | rather than its internal branch table, thereby loading in the |
429 | existing value of the branch. | |
430 | ||
431 | `merge` | |
432 | ^^^^^^^ | |
9b33fa08 EB |
433 | Includes one additional ancestor commit. If the `from` command is |
434 | omitted when creating a new branch, the first `merge` commit will be | |
435 | the first ancestor of the current commit, and the branch will start | |
436 | out with no files. An unlimited number of `merge` commands per | |
882227f1 | 437 | commit are permitted by fast-import, thereby establishing an n-way merge. |
6e411d20 SP |
438 | However Git's other tools never create commits with more than 15 |
439 | additional ancestors (forming a 16-way merge). For this reason | |
440 | it is suggested that frontends do not use more than 15 `merge` | |
9b33fa08 | 441 | commands per commit; 16, if starting a new, empty branch. |
6e411d20 SP |
442 | |
443 | Here `<committish>` is any of the commit specification expressions | |
444 | also accepted by `from` (see above). | |
445 | ||
446 | `filemodify` | |
ef94edb5 | 447 | ^^^^^^^^^^^^ |
6e411d20 SP |
448 | Included in a `commit` command to add a new file or change the |
449 | content of an existing file. This command has two different means | |
450 | of specifying the content of the file. | |
451 | ||
452 | External data format:: | |
453 | The data content for the file was already supplied by a prior | |
454 | `blob` command. The frontend just needs to connect it. | |
455 | + | |
456 | .... | |
457 | 'M' SP <mode> SP <dataref> SP <path> LF | |
458 | .... | |
459 | + | |
460 | Here `<dataref>` can be either a mark reference (`:<idnum>`) | |
461 | set by a prior `blob` command, or a full 40-byte SHA-1 of an | |
462 | existing Git blob object. | |
463 | ||
464 | Inline data format:: | |
465 | The data content for the file has not been supplied yet. | |
466 | The frontend wants to supply it as part of this modify | |
467 | command. | |
468 | + | |
469 | .... | |
470 | 'M' SP <mode> SP 'inline' SP <path> LF | |
471 | data | |
472 | .... | |
473 | + | |
474 | See below for a detailed description of the `data` command. | |
475 | ||
476 | In both formats `<mode>` is the type of file entry, specified | |
477 | in octal. Git only supports the following modes: | |
478 | ||
479 | * `100644` or `644`: A normal (not-executable) file. The majority | |
480 | of files in most projects use this mode. If in doubt, this is | |
481 | what you want. | |
482 | * `100755` or `755`: A normal, but executable, file. | |
9981b6d9 | 483 | * `120000`: A symlink, the content of the file will be the link target. |
03db4525 AG |
484 | * `160000`: A gitlink, SHA-1 of the object refers to a commit in |
485 | another repository. Git links can only be specified by SHA or through | |
486 | a commit mark. They are used to implement submodules. | |
6e411d20 SP |
487 | |
488 | In both formats `<path>` is the complete path of the file to be added | |
489 | (if not already existing) or modified (if already existing). | |
490 | ||
c4431d38 | 491 | A `<path>` string must use UNIX-style directory separators (forward |
6e411d20 SP |
492 | slash `/`), may contain any byte other than `LF`, and must not |
493 | start with double quote (`"`). | |
494 | ||
495 | If an `LF` or double quote must be encoded into `<path>` shell-style | |
496 | quoting should be used, e.g. `"path/with\n and \" in it"`. | |
497 | ||
02783075 | 498 | The value of `<path>` must be in canonical form. That is it must not: |
6e411d20 SP |
499 | |
500 | * contain an empty directory component (e.g. `foo//bar` is invalid), | |
c4431d38 JK |
501 | * end with a directory separator (e.g. `foo/` is invalid), |
502 | * start with a directory separator (e.g. `/foo` is invalid), | |
6e411d20 SP |
503 | * contain the special component `.` or `..` (e.g. `foo/./bar` and |
504 | `foo/../bar` are invalid). | |
505 | ||
506 | It is recommended that `<path>` always be encoded using UTF-8. | |
507 | ||
6e411d20 | 508 | `filedelete` |
ef94edb5 | 509 | ^^^^^^^^^^^^ |
512e44b2 SP |
510 | Included in a `commit` command to remove a file or recursively |
511 | delete an entire directory from the branch. If the file or directory | |
512 | removal makes its parent directory empty, the parent directory will | |
6e411d20 SP |
513 | be automatically removed too. This cascades up the tree until the |
514 | first non-empty directory or the root is reached. | |
515 | ||
516 | .... | |
517 | 'D' SP <path> LF | |
518 | .... | |
519 | ||
512e44b2 SP |
520 | here `<path>` is the complete path of the file or subdirectory to |
521 | be removed from the branch. | |
6e411d20 SP |
522 | See `filemodify` above for a detailed description of `<path>`. |
523 | ||
b6f3481b SP |
524 | `filecopy` |
525 | ^^^^^^^^^^^^ | |
526 | Recursively copies an existing file or subdirectory to a different | |
527 | location within the branch. The existing file or directory must | |
528 | exist. If the destination exists it will be completely replaced | |
529 | by the content copied from the source. | |
530 | ||
531 | .... | |
532 | 'C' SP <path> SP <path> LF | |
533 | .... | |
534 | ||
535 | here the first `<path>` is the source location and the second | |
536 | `<path>` is the destination. See `filemodify` above for a detailed | |
537 | description of what `<path>` may look like. To use a source path | |
538 | that contains SP the path must be quoted. | |
539 | ||
540 | A `filecopy` command takes effect immediately. Once the source | |
541 | location has been copied to the destination any future commands | |
542 | applied to the source location will not impact the destination of | |
543 | the copy. | |
544 | ||
f39a946a SP |
545 | `filerename` |
546 | ^^^^^^^^^^^^ | |
547 | Renames an existing file or subdirectory to a different location | |
548 | within the branch. The existing file or directory must exist. If | |
549 | the destination exists it will be replaced by the source directory. | |
550 | ||
551 | .... | |
552 | 'R' SP <path> SP <path> LF | |
553 | .... | |
554 | ||
555 | here the first `<path>` is the source location and the second | |
556 | `<path>` is the destination. See `filemodify` above for a detailed | |
557 | description of what `<path>` may look like. To use a source path | |
558 | that contains SP the path must be quoted. | |
559 | ||
560 | A `filerename` command takes effect immediately. Once the source | |
561 | location has been renamed to the destination any future commands | |
562 | applied to the source location will create new files there and not | |
563 | impact the destination of the rename. | |
564 | ||
b6f3481b SP |
565 | Note that a `filerename` is the same as a `filecopy` followed by a |
566 | `filedelete` of the source location. There is a slight performance | |
567 | advantage to using `filerename`, but the advantage is so small | |
568 | that it is never worth trying to convert a delete/add pair in | |
569 | source material into a rename for fast-import. This `filerename` | |
570 | command is provided just to simplify frontends that already have | |
571 | rename information and don't want bother with decomposing it into a | |
572 | `filecopy` followed by a `filedelete`. | |
573 | ||
825769a8 SP |
574 | `filedeleteall` |
575 | ^^^^^^^^^^^^^^^ | |
576 | Included in a `commit` command to remove all files (and also all | |
577 | directories) from the branch. This command resets the internal | |
578 | branch structure to have no files in it, allowing the frontend | |
579 | to subsequently add all interesting files from scratch. | |
580 | ||
581 | .... | |
582 | 'deleteall' LF | |
583 | .... | |
584 | ||
585 | This command is extremely useful if the frontend does not know | |
586 | (or does not care to know) what files are currently on the branch, | |
587 | and therefore cannot generate the proper `filedelete` commands to | |
588 | update the content. | |
589 | ||
590 | Issuing a `filedeleteall` followed by the needed `filemodify` | |
591 | commands to set the correct content will produce the same results | |
592 | as sending only the needed `filemodify` and `filedelete` commands. | |
882227f1 | 593 | The `filedeleteall` approach may however require fast-import to use slightly |
825769a8 SP |
594 | more memory per active branch (less than 1 MiB for even most large |
595 | projects); so frontends that can easily obtain only the affected | |
596 | paths for a commit are encouraged to do so. | |
597 | ||
6e411d20 SP |
598 | `mark` |
599 | ~~~~~~ | |
882227f1 | 600 | Arranges for fast-import to save a reference to the current object, allowing |
6e411d20 SP |
601 | the frontend to recall this object at a future point in time, without |
602 | knowing its SHA-1. Here the current object is the object creation | |
603 | command the `mark` command appears within. This can be `commit`, | |
604 | `tag`, and `blob`, but `commit` is the most common usage. | |
605 | ||
606 | .... | |
607 | 'mark' SP ':' <idnum> LF | |
608 | .... | |
609 | ||
610 | where `<idnum>` is the number assigned by the frontend to this mark. | |
ef94edb5 SP |
611 | The value of `<idnum>` is expressed as an ASCII decimal integer. |
612 | The value 0 is reserved and cannot be used as | |
6e411d20 SP |
613 | a mark. Only values greater than or equal to 1 may be used as marks. |
614 | ||
615 | New marks are created automatically. Existing marks can be moved | |
616 | to another object simply by reusing the same `<idnum>` in another | |
617 | `mark` command. | |
618 | ||
619 | `tag` | |
620 | ~~~~~ | |
621 | Creates an annotated tag referring to a specific commit. To create | |
622 | lightweight (non-annotated) tags see the `reset` command below. | |
623 | ||
624 | .... | |
625 | 'tag' SP <name> LF | |
626 | 'from' SP <committish> LF | |
63e0c8b3 | 627 | 'tagger' SP <name> SP LT <email> GT SP <when> LF |
6e411d20 | 628 | data |
6e411d20 SP |
629 | .... |
630 | ||
631 | where `<name>` is the name of the tag to create. | |
632 | ||
633 | Tag names are automatically prefixed with `refs/tags/` when stored | |
634 | in Git, so importing the CVS branch symbol `RELENG-1_0-FINAL` would | |
882227f1 | 635 | use just `RELENG-1_0-FINAL` for `<name>`, and fast-import will write the |
6e411d20 SP |
636 | corresponding ref as `refs/tags/RELENG-1_0-FINAL`. |
637 | ||
638 | The value of `<name>` must be a valid refname in Git and therefore | |
639 | may contain forward slashes. As `LF` is not valid in a Git refname, | |
640 | no quoting or escaping syntax is supported here. | |
641 | ||
642 | The `from` command is the same as in the `commit` command; see | |
643 | above for details. | |
644 | ||
645 | The `tagger` command uses the same format as `committer` within | |
646 | `commit`; again see above for details. | |
647 | ||
648 | The `data` command following `tagger` must supply the annotated tag | |
649 | message (see below for `data` command syntax). To import an empty | |
650 | tag message use a 0 length data. Tag messages are free-form and are | |
651 | not interpreted by Git. Currently they must be encoded in UTF-8, | |
882227f1 | 652 | as fast-import does not permit other encodings to be specified. |
6e411d20 | 653 | |
882227f1 | 654 | Signing annotated tags during import from within fast-import is not |
6e411d20 SP |
655 | supported. Trying to include your own PGP/GPG signature is not |
656 | recommended, as the frontend does not (easily) have access to the | |
657 | complete set of bytes which normally goes into such a signature. | |
882227f1 | 658 | If signing is required, create lightweight tags from within fast-import with |
6e411d20 | 659 | `reset`, then create the annotated versions of those tags offline |
ba020ef5 | 660 | with the standard 'git-tag' process. |
6e411d20 SP |
661 | |
662 | `reset` | |
663 | ~~~~~~~ | |
664 | Creates (or recreates) the named branch, optionally starting from | |
665 | a specific revision. The reset command allows a frontend to issue | |
666 | a new `from` command for an existing branch, or to create a new | |
667 | branch from an existing commit without creating a new commit. | |
668 | ||
669 | .... | |
670 | 'reset' SP <ref> LF | |
671 | ('from' SP <committish> LF)? | |
1fdb649c | 672 | LF? |
6e411d20 SP |
673 | .... |
674 | ||
675 | For a detailed description of `<ref>` and `<committish>` see above | |
676 | under `commit` and `from`. | |
677 | ||
1fdb649c SP |
678 | The `LF` after the command is optional (it used to be required). |
679 | ||
6e411d20 SP |
680 | The `reset` command can also be used to create lightweight |
681 | (non-annotated) tags. For example: | |
682 | ||
683 | ==== | |
684 | reset refs/tags/938 | |
685 | from :938 | |
686 | ==== | |
687 | ||
688 | would create the lightweight tag `refs/tags/938` referring to | |
689 | whatever commit mark `:938` references. | |
690 | ||
691 | `blob` | |
692 | ~~~~~~ | |
693 | Requests writing one file revision to the packfile. The revision | |
694 | is not connected to any commit; this connection must be formed in | |
695 | a subsequent `commit` command by referencing the blob through an | |
696 | assigned mark. | |
697 | ||
698 | .... | |
699 | 'blob' LF | |
700 | mark? | |
701 | data | |
702 | .... | |
703 | ||
704 | The mark command is optional here as some frontends have chosen | |
705 | to generate the Git SHA-1 for the blob on their own, and feed that | |
706 | directly to `commit`. This is typically more work than its worth | |
707 | however, as marks are inexpensive to store and easy to use. | |
708 | ||
709 | `data` | |
710 | ~~~~~~ | |
711 | Supplies raw data (for use as blob/file content, commit messages, or | |
882227f1 | 712 | annotated tag messages) to fast-import. Data can be supplied using an exact |
6e411d20 SP |
713 | byte count or delimited with a terminating line. Real frontends |
714 | intended for production-quality conversions should always use the | |
715 | exact byte count format, as it is more robust and performs better. | |
882227f1 | 716 | The delimited format is intended primarily for testing fast-import. |
6e411d20 | 717 | |
401d53fa SP |
718 | Comment lines appearing within the `<raw>` part of `data` commands |
719 | are always taken to be part of the body of the data and are therefore | |
720 | never ignored by fast-import. This makes it safe to import any | |
721 | file/message content whose lines might start with `#`. | |
722 | ||
ef94edb5 SP |
723 | Exact byte count format:: |
724 | The frontend must specify the number of bytes of data. | |
725 | + | |
6e411d20 SP |
726 | .... |
727 | 'data' SP <count> LF | |
2c570cde | 728 | <raw> LF? |
6e411d20 | 729 | .... |
ef94edb5 | 730 | + |
6e411d20 | 731 | where `<count>` is the exact number of bytes appearing within |
ef94edb5 SP |
732 | `<raw>`. The value of `<count>` is expressed as an ASCII decimal |
733 | integer. The `LF` on either side of `<raw>` is not | |
6e411d20 | 734 | included in `<count>` and will not be included in the imported data. |
2c570cde SP |
735 | + |
736 | The `LF` after `<raw>` is optional (it used to be required) but | |
737 | recommended. Always including it makes debugging a fast-import | |
738 | stream easier as the next command always starts in column 0 | |
739 | of the next line, even if `<raw>` did not end with an `LF`. | |
6e411d20 | 740 | |
ef94edb5 SP |
741 | Delimited format:: |
742 | A delimiter string is used to mark the end of the data. | |
882227f1 | 743 | fast-import will compute the length by searching for the delimiter. |
02783075 | 744 | This format is primarily useful for testing and is not |
ef94edb5 SP |
745 | recommended for real data. |
746 | + | |
6e411d20 SP |
747 | .... |
748 | 'data' SP '<<' <delim> LF | |
749 | <raw> LF | |
750 | <delim> LF | |
2c570cde | 751 | LF? |
6e411d20 | 752 | .... |
ef94edb5 | 753 | + |
6e411d20 SP |
754 | where `<delim>` is the chosen delimiter string. The string `<delim>` |
755 | must not appear on a line by itself within `<raw>`, as otherwise | |
882227f1 | 756 | fast-import will think the data ends earlier than it really does. The `LF` |
6e411d20 SP |
757 | immediately trailing `<raw>` is part of `<raw>`. This is one of |
758 | the limitations of the delimited format, it is impossible to supply | |
759 | a data chunk which does not have an LF as its last byte. | |
2c570cde SP |
760 | + |
761 | The `LF` after `<delim> LF` is optional (it used to be required). | |
6e411d20 SP |
762 | |
763 | `checkpoint` | |
764 | ~~~~~~~~~~~~ | |
882227f1 | 765 | Forces fast-import to close the current packfile, start a new one, and to |
820b9310 | 766 | save out all current branch refs, tags and marks. |
6e411d20 SP |
767 | |
768 | .... | |
769 | 'checkpoint' LF | |
1fdb649c | 770 | LF? |
6e411d20 SP |
771 | .... |
772 | ||
882227f1 | 773 | Note that fast-import automatically switches packfiles when the current |
820b9310 | 774 | packfile reaches \--max-pack-size, or 4 GiB, whichever limit is |
882227f1 | 775 | smaller. During an automatic packfile switch fast-import does not update |
820b9310 SP |
776 | the branch refs, tags or marks. |
777 | ||
778 | As a `checkpoint` can require a significant amount of CPU time and | |
779 | disk IO (to compute the overall pack SHA-1 checksum, generate the | |
780 | corresponding index file, and update the refs) it can easily take | |
781 | several minutes for a single `checkpoint` command to complete. | |
782 | ||
783 | Frontends may choose to issue checkpoints during extremely large | |
784 | and long running imports, or when they need to allow another Git | |
785 | process access to a branch. However given that a 30 GiB Subversion | |
882227f1 | 786 | repository can be loaded into Git through fast-import in about 3 hours, |
820b9310 SP |
787 | explicit checkpointing may not be necessary. |
788 | ||
1fdb649c | 789 | The `LF` after the command is optional (it used to be required). |
820b9310 | 790 | |
ac053c02 SP |
791 | `progress` |
792 | ~~~~~~~~~~ | |
793 | Causes fast-import to print the entire `progress` line unmodified to | |
794 | its standard output channel (file descriptor 1) when the command is | |
795 | processed from the input stream. The command otherwise has no impact | |
796 | on the current import, or on any of fast-import's internal state. | |
797 | ||
798 | .... | |
799 | 'progress' SP <any> LF | |
800 | LF? | |
801 | .... | |
802 | ||
803 | The `<any>` part of the command may contain any sequence of bytes | |
804 | that does not contain `LF`. The `LF` after the command is optional. | |
805 | Callers may wish to process the output through a tool such as sed to | |
806 | remove the leading part of the line, for example: | |
807 | ||
808 | ==== | |
b1889c36 | 809 | frontend | git fast-import | sed 's/^progress //' |
ac053c02 SP |
810 | ==== |
811 | ||
812 | Placing a `progress` command immediately after a `checkpoint` will | |
813 | inform the reader when the `checkpoint` has been completed and it | |
814 | can safely access the refs that fast-import updated. | |
815 | ||
e7e5170f SP |
816 | Crash Reports |
817 | ------------- | |
818 | If fast-import is supplied invalid input it will terminate with a | |
819 | non-zero exit status and create a crash report in the top level of | |
820 | the Git repository it was importing into. Crash reports contain | |
821 | a snapshot of the internal fast-import state as well as the most | |
822 | recent commands that lead up to the crash. | |
823 | ||
824 | All recent commands (including stream comments, file changes and | |
825 | progress commands) are shown in the command history within the crash | |
826 | report, but raw file data and commit messages are excluded from the | |
827 | crash report. This exclusion saves space within the report file | |
828 | and reduces the amount of buffering that fast-import must perform | |
829 | during execution. | |
830 | ||
831 | After writing a crash report fast-import will close the current | |
832 | packfile and export the marks table. This allows the frontend | |
833 | developer to inspect the repository state and resume the import from | |
834 | the point where it crashed. The modified branches and tags are not | |
835 | updated during a crash, as the import did not complete successfully. | |
836 | Branch and tag information can be found in the crash report and | |
837 | must be applied manually if the update is needed. | |
838 | ||
839 | An example crash: | |
840 | ||
841 | ==== | |
842 | $ cat >in <<END_OF_INPUT | |
843 | # my very first test commit | |
844 | commit refs/heads/master | |
845 | committer Shawn O. Pearce <spearce> 19283 -0400 | |
846 | # who is that guy anyway? | |
847 | data <<EOF | |
848 | this is my commit | |
849 | EOF | |
850 | M 644 inline .gitignore | |
851 | data <<EOF | |
852 | .gitignore | |
853 | EOF | |
854 | M 777 inline bob | |
855 | END_OF_INPUT | |
856 | ||
b1889c36 | 857 | $ git fast-import <in |
e7e5170f SP |
858 | fatal: Corrupt mode: M 777 inline bob |
859 | fast-import: dumping crash report to .git/fast_import_crash_8434 | |
860 | ||
861 | $ cat .git/fast_import_crash_8434 | |
862 | fast-import crash report: | |
863 | fast-import process: 8434 | |
864 | parent process : 1391 | |
865 | at Sat Sep 1 00:58:12 2007 | |
866 | ||
867 | fatal: Corrupt mode: M 777 inline bob | |
868 | ||
869 | Most Recent Commands Before Crash | |
870 | --------------------------------- | |
871 | # my very first test commit | |
872 | commit refs/heads/master | |
873 | committer Shawn O. Pearce <spearce> 19283 -0400 | |
874 | # who is that guy anyway? | |
875 | data <<EOF | |
876 | M 644 inline .gitignore | |
877 | data <<EOF | |
878 | * M 777 inline bob | |
879 | ||
880 | Active Branch LRU | |
881 | ----------------- | |
882 | active_branches = 1 cur, 5 max | |
883 | ||
884 | pos clock name | |
885 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
886 | 1) 0 refs/heads/master | |
887 | ||
888 | Inactive Branches | |
889 | ----------------- | |
890 | refs/heads/master: | |
891 | status : active loaded dirty | |
892 | tip commit : 0000000000000000000000000000000000000000 | |
893 | old tree : 0000000000000000000000000000000000000000 | |
894 | cur tree : 0000000000000000000000000000000000000000 | |
895 | commit clock: 0 | |
896 | last pack : | |
897 | ||
898 | ||
899 | ------------------- | |
900 | END OF CRASH REPORT | |
901 | ==== | |
902 | ||
bdd9f424 SP |
903 | Tips and Tricks |
904 | --------------- | |
905 | The following tips and tricks have been collected from various | |
882227f1 | 906 | users of fast-import, and are offered here as suggestions. |
bdd9f424 SP |
907 | |
908 | Use One Mark Per Commit | |
909 | ~~~~~~~~~~~~~~~~~~~~~~~ | |
910 | When doing a repository conversion, use a unique mark per commit | |
911 | (`mark :<n>`) and supply the \--export-marks option on the command | |
882227f1 | 912 | line. fast-import will dump a file which lists every mark and the Git |
bdd9f424 SP |
913 | object SHA-1 that corresponds to it. If the frontend can tie |
914 | the marks back to the source repository, it is easy to verify the | |
915 | accuracy and completeness of the import by comparing each Git | |
916 | commit to the corresponding source revision. | |
917 | ||
918 | Coming from a system such as Perforce or Subversion this should be | |
882227f1 | 919 | quite simple, as the fast-import mark can also be the Perforce changeset |
bdd9f424 SP |
920 | number or the Subversion revision number. |
921 | ||
922 | Freely Skip Around Branches | |
923 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
924 | Don't bother trying to optimize the frontend to stick to one branch | |
925 | at a time during an import. Although doing so might be slightly | |
882227f1 | 926 | faster for fast-import, it tends to increase the complexity of the frontend |
bdd9f424 SP |
927 | code considerably. |
928 | ||
882227f1 | 929 | The branch LRU builtin to fast-import tends to behave very well, and the |
bdd9f424 SP |
930 | cost of activating an inactive branch is so low that bouncing around |
931 | between branches has virtually no impact on import performance. | |
932 | ||
c7346156 SP |
933 | Handling Renames |
934 | ~~~~~~~~~~~~~~~~ | |
935 | When importing a renamed file or directory, simply delete the old | |
936 | name(s) and modify the new name(s) during the corresponding commit. | |
937 | Git performs rename detection after-the-fact, rather than explicitly | |
938 | during a commit. | |
939 | ||
bdd9f424 SP |
940 | Use Tag Fixup Branches |
941 | ~~~~~~~~~~~~~~~~~~~~~~ | |
942 | Some other SCM systems let the user create a tag from multiple | |
943 | files which are not from the same commit/changeset. Or to create | |
944 | tags which are a subset of the files available in the repository. | |
945 | ||
946 | Importing these tags as-is in Git is impossible without making at | |
947 | least one commit which ``fixes up'' the files to match the content | |
882227f1 | 948 | of the tag. Use fast-import's `reset` command to reset a dummy branch |
bdd9f424 SP |
949 | outside of your normal branch space to the base commit for the tag, |
950 | then commit one or more file fixup commits, and finally tag the | |
951 | dummy branch. | |
952 | ||
953 | For example since all normal branches are stored under `refs/heads/` | |
954 | name the tag fixup branch `TAG_FIXUP`. This way it is impossible for | |
955 | the fixup branch used by the importer to have namespace conflicts | |
956 | with real branches imported from the source (the name `TAG_FIXUP` | |
957 | is not `refs/heads/TAG_FIXUP`). | |
958 | ||
959 | When committing fixups, consider using `merge` to connect the | |
960 | commit(s) which are supplying file revisions to the fixup branch. | |
ba020ef5 | 961 | Doing so will allow tools such as 'git-blame' to track |
bdd9f424 SP |
962 | through the real commit history and properly annotate the source |
963 | files. | |
964 | ||
882227f1 | 965 | After fast-import terminates the frontend will need to do `rm .git/TAG_FIXUP` |
bdd9f424 SP |
966 | to remove the dummy branch. |
967 | ||
968 | Import Now, Repack Later | |
969 | ~~~~~~~~~~~~~~~~~~~~~~~~ | |
882227f1 | 970 | As soon as fast-import completes the Git repository is completely valid |
02783075 | 971 | and ready for use. Typically this takes only a very short time, |
bdd9f424 SP |
972 | even for considerably large projects (100,000+ commits). |
973 | ||
974 | However repacking the repository is necessary to improve data | |
975 | locality and access performance. It can also take hours on extremely | |
976 | large projects (especially if -f and a large \--window parameter is | |
977 | used). Since repacking is safe to run alongside readers and writers, | |
978 | run the repack in the background and let it finish when it finishes. | |
979 | There is no reason to wait to explore your new Git project! | |
980 | ||
981 | If you choose to wait for the repack, don't try to run benchmarks | |
882227f1 | 982 | or performance tests until repacking is completed. fast-import outputs |
bdd9f424 SP |
983 | suboptimal packfiles that are simply never seen in real use |
984 | situations. | |
985 | ||
986 | Repacking Historical Data | |
987 | ~~~~~~~~~~~~~~~~~~~~~~~~~ | |
988 | If you are repacking very old imported data (e.g. older than the | |
989 | last year), consider expending some extra CPU time and supplying | |
ba020ef5 | 990 | \--window=50 (or higher) when you run 'git-repack'. |
bdd9f424 SP |
991 | This will take longer, but will also produce a smaller packfile. |
992 | You only need to expend the effort once, and everyone using your | |
993 | project will benefit from the smaller repository. | |
994 | ||
ac053c02 SP |
995 | Include Some Progress Messages |
996 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
997 | Every once in a while have your frontend emit a `progress` message | |
998 | to fast-import. The contents of the messages are entirely free-form, | |
999 | so one suggestion would be to output the current month and year | |
1000 | each time the current commit date moves into the next month. | |
1001 | Your users will feel better knowing how much of the data stream | |
1002 | has been processed. | |
1003 | ||
bdd9f424 | 1004 | |
6e411d20 SP |
1005 | Packfile Optimization |
1006 | --------------------- | |
882227f1 | 1007 | When packing a blob fast-import always attempts to deltify against the last |
6e411d20 SP |
1008 | blob written. Unless specifically arranged for by the frontend, |
1009 | this will probably not be a prior version of the same file, so the | |
1010 | generated delta will not be the smallest possible. The resulting | |
1011 | packfile will be compressed, but will not be optimal. | |
1012 | ||
1013 | Frontends which have efficient access to all revisions of a | |
1014 | single file (for example reading an RCS/CVS ,v file) can choose | |
1015 | to supply all revisions of that file as a sequence of consecutive | |
882227f1 | 1016 | `blob` commands. This allows fast-import to deltify the different file |
6e411d20 SP |
1017 | revisions against each other, saving space in the final packfile. |
1018 | Marks can be used to later identify individual file revisions during | |
1019 | a sequence of `commit` commands. | |
1020 | ||
882227f1 SP |
1021 | The packfile(s) created by fast-import do not encourage good disk access |
1022 | patterns. This is caused by fast-import writing the data in the order | |
6e411d20 SP |
1023 | it is received on standard input, while Git typically organizes |
1024 | data within packfiles to make the most recent (current tip) data | |
1025 | appear before historical data. Git also clusters commits together, | |
1026 | speeding up revision traversal through better cache locality. | |
1027 | ||
1028 | For this reason it is strongly recommended that users repack the | |
882227f1 | 1029 | repository with `git repack -a -d` after fast-import completes, allowing |
6e411d20 SP |
1030 | Git to reorganize the packfiles for faster data access. If blob |
1031 | deltas are suboptimal (see above) then also adding the `-f` option | |
1032 | to force recomputation of all deltas can significantly reduce the | |
1033 | final packfile size (30-50% smaller can be quite typical). | |
1034 | ||
bdd9f424 | 1035 | |
6e411d20 SP |
1036 | Memory Utilization |
1037 | ------------------ | |
882227f1 | 1038 | There are a number of factors which affect how much memory fast-import |
6e411d20 | 1039 | requires to perform an import. Like critical sections of core |
02783075 BH |
1040 | Git, fast-import uses its own memory allocators to amortize any overheads |
1041 | associated with malloc. In practice fast-import tends to amortize any | |
6e411d20 SP |
1042 | malloc overheads to 0, due to its use of large block allocations. |
1043 | ||
1044 | per object | |
1045 | ~~~~~~~~~~ | |
882227f1 | 1046 | fast-import maintains an in-memory structure for every object written in |
6e411d20 SP |
1047 | this execution. On a 32 bit system the structure is 32 bytes, |
1048 | on a 64 bit system the structure is 40 bytes (due to the larger | |
1049 | pointer sizes). Objects in the table are not deallocated until | |
882227f1 | 1050 | fast-import terminates. Importing 2 million objects on a 32 bit system |
6e411d20 SP |
1051 | will require approximately 64 MiB of memory. |
1052 | ||
1053 | The object table is actually a hashtable keyed on the object name | |
882227f1 | 1054 | (the unique SHA-1). This storage configuration allows fast-import to reuse |
6e411d20 SP |
1055 | an existing or already written object and avoid writing duplicates |
1056 | to the output packfile. Duplicate blobs are surprisingly common | |
1057 | in an import, typically due to branch merges in the source. | |
1058 | ||
1059 | per mark | |
1060 | ~~~~~~~~ | |
1061 | Marks are stored in a sparse array, using 1 pointer (4 bytes or 8 | |
1062 | bytes, depending on pointer size) per mark. Although the array | |
1063 | is sparse, frontends are still strongly encouraged to use marks | |
1064 | between 1 and n, where n is the total number of marks required for | |
1065 | this import. | |
1066 | ||
1067 | per branch | |
1068 | ~~~~~~~~~~ | |
1069 | Branches are classified as active and inactive. The memory usage | |
1070 | of the two classes is significantly different. | |
1071 | ||
1072 | Inactive branches are stored in a structure which uses 96 or 120 | |
1073 | bytes (32 bit or 64 bit systems, respectively), plus the length of | |
882227f1 | 1074 | the branch name (typically under 200 bytes), per branch. fast-import will |
6e411d20 SP |
1075 | easily handle as many as 10,000 inactive branches in under 2 MiB |
1076 | of memory. | |
1077 | ||
1078 | Active branches have the same overhead as inactive branches, but | |
1079 | also contain copies of every tree that has been recently modified on | |
1080 | that branch. If subtree `include` has not been modified since the | |
1081 | branch became active, its contents will not be loaded into memory, | |
1082 | but if subtree `src` has been modified by a commit since the branch | |
1083 | became active, then its contents will be loaded in memory. | |
1084 | ||
1085 | As active branches store metadata about the files contained on that | |
1086 | branch, their in-memory storage size can grow to a considerable size | |
1087 | (see below). | |
1088 | ||
882227f1 | 1089 | fast-import automatically moves active branches to inactive status based on |
6e411d20 SP |
1090 | a simple least-recently-used algorithm. The LRU chain is updated on |
1091 | each `commit` command. The maximum number of active branches can be | |
c499d768 | 1092 | increased or decreased on the command line with \--active-branches=. |
6e411d20 SP |
1093 | |
1094 | per active tree | |
1095 | ~~~~~~~~~~~~~~~ | |
1096 | Trees (aka directories) use just 12 bytes of memory on top of the | |
1097 | memory required for their entries (see ``per active file'' below). | |
02783075 | 1098 | The cost of a tree is virtually 0, as its overhead amortizes out |
6e411d20 SP |
1099 | over the individual file entries. |
1100 | ||
1101 | per active file entry | |
1102 | ~~~~~~~~~~~~~~~~~~~~~ | |
1103 | Files (and pointers to subtrees) within active trees require 52 or 64 | |
1104 | bytes (32/64 bit platforms) per entry. To conserve space, file and | |
1105 | tree names are pooled in a common string table, allowing the filename | |
1106 | ``Makefile'' to use just 16 bytes (after including the string header | |
1107 | overhead) no matter how many times it occurs within the project. | |
1108 | ||
1109 | The active branch LRU, when coupled with the filename string pool | |
882227f1 | 1110 | and lazy loading of subtrees, allows fast-import to efficiently import |
6e411d20 SP |
1111 | projects with 2,000+ branches and 45,114+ files in a very limited |
1112 | memory footprint (less than 2.7 MiB per active branch). | |
1113 | ||
1114 | ||
1115 | Author | |
1116 | ------ | |
1117 | Written by Shawn O. Pearce <spearce@spearce.org>. | |
1118 | ||
1119 | Documentation | |
1120 | -------------- | |
1121 | Documentation by Shawn O. Pearce <spearce@spearce.org>. | |
1122 | ||
1123 | GIT | |
1124 | --- | |
9e1f0a85 | 1125 | Part of the linkgit:git[1] suite |