1git-fast-import(1) 2================== 3 4NAME 5---- 6git-fast-import - Backend for fast Git data importers 7 8 9SYNOPSIS 10-------- 11frontend | 'git fast-import' [options] 12 13DESCRIPTION 14----------- 15This program is usually not what the end user wants to run directly. 16Most end users want to use one of the existing frontend programs, 17which parses a specific type of foreign source and feeds the contents 18stored there to 'git-fast-import'. 19 20fast-import reads a mixed command/data stream from standard input and 21writes one or more packfiles directly into the current repository. 22When EOF is received on standard input, fast import writes out 23updated branch and tag refs, fully updating the current repository 24with the newly imported data. 25 26The fast-import backend itself can import into an empty repository (one that 27has already been initialized by 'git-init') or incrementally 28update an existing populated repository. Whether or not incremental 29imports are supported from a particular foreign source depends on 30the frontend program in use. 31 32 33OPTIONS 34------- 35--date-format=<fmt>:: 36 Specify the type of dates the frontend will supply to 37 fast-import within `author`, `committer` and `tagger` commands. 38 See ``Date Formats'' below for details about which formats 39 are supported, and their syntax. 40 41--force:: 42 Force updating modified existing branches, even if doing 43 so would cause commits to be lost (as the new commit does 44 not contain the old commit). 45 46--max-pack-size=<n>:: 47 Maximum size of each output packfile, 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 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. 77 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 85 to 'git-pack-objects'. 86 87--quiet:: 88 Disable all non-fatal output, making fast-import silent when it 89 is successful. This option disables the output shown by 90 \--stats. 91 92--stats:: 93 Display some basic statistics about the objects fast-import has 94 created, the packfiles they were stored into, and the 95 memory used by fast-import during this run. Showing this output 96 is currently the default, but can be disabled with \--quiet. 97 98 99Performance 100----------- 101The design of fast-import allows it to import large projects in a minimum 102amount of memory usage and processing time. Assuming the frontend 103is able to keep up with fast-import and feed it a constant stream of data, 104import times for projects holding 10+ years of history and containing 105100,000+ individual commits are generally completed in just 1-2 106hours on quite modest (~$2,000 USD) hardware. 107 108Most bottlenecks appear to be in foreign source data access (the 109source just cannot extract revisions fast enough) or disk IO (fast-import 110writes as fast as the disk will take the data). Imports will run 111faster if the source data is stored on a different drive than the 112destination Git repository (due to less IO contention). 113 114 115Development Cost 116---------------- 117A typical frontend for fast-import tends to weigh in at approximately 200 118lines of Perl/Python/Ruby code. Most developers have been able to 119create working importers in just a couple of hours, even though it 120is their first exposure to fast-import, and sometimes even to Git. This is 121an ideal situation, given that most conversion tools are throw-away 122(use once, and never look back). 123 124 125Parallel Operation 126------------------ 127Like 'git-push' or 'git-fetch', imports handled by fast-import are safe to 128run alongside parallel `git repack -a -d` or `git gc` invocations, 129or any other Git operation (including 'git-prune', as loose objects 130are never used by fast-import). 131 132fast-import does not lock the branch or tag refs it is actively importing. 133After the import, during its ref update phase, fast-import tests each 134existing branch ref to verify the update will be a fast-forward 135update (the commit stored in the ref is contained in the new 136history of the commit to be written). If the update is not a 137fast-forward update, fast-import will skip updating that ref and instead 138prints a warning message. fast-import will always attempt to update all 139branch refs, and does not stop on the first failure. 140 141Branch updates can be forced with \--force, but its recommended that 142this only be used on an otherwise quiet repository. Using \--force 143is not necessary for an initial import into an empty repository. 144 145 146Technical Discussion 147-------------------- 148fast-import tracks a set of branches in memory. Any branch can be created 149or modified at any point during the import process by sending a 150`commit` command on the input stream. This design allows a frontend 151program to process an unlimited number of branches simultaneously, 152generating commits in the order they are available from the source 153data. It also simplifies the frontend programs considerably. 154 155fast-import does not use or alter the current working directory, or any 156file within it. (It does however update the current Git repository, 157as referenced by `GIT_DIR`.) Therefore an import frontend may use 158the working directory for its own purposes, such as extracting file 159revisions from the foreign source. This ignorance of the working 160directory also allows fast-import to run very quickly, as it does not 161need to perform any costly file update operations when switching 162between branches. 163 164Input Format 165------------ 166With the exception of raw file data (which Git does not interpret) 167the fast-import input format is text (ASCII) based. This text based 168format simplifies development and debugging of frontend programs, 169especially when a higher level language such as Perl, Python or 170Ruby is being used. 171 172fast-import is very strict about its input. Where we say SP below we mean 173*exactly* one space. Likewise LF means one (and only one) linefeed. 174Supplying additional whitespace characters will cause unexpected 175results, such as branch names or file names with leading or trailing 176spaces in their name, or early termination of fast-import when it encounters 177unexpected input. 178 179Stream Comments 180~~~~~~~~~~~~~~~ 181To aid in debugging frontends fast-import ignores any line that 182begins with `#` (ASCII pound/hash) up to and including the line 183ending `LF`. A comment line may contain any sequence of bytes 184that does not contain an LF and therefore may be used to include 185any detailed debugging information that might be specific to the 186frontend and useful when inspecting a fast-import data stream. 187 188Date Formats 189~~~~~~~~~~~~ 190The following date formats are supported. A frontend should select 191the format it will use for this import by passing the format name 192in the \--date-format=<fmt> command line option. 193 194`raw`:: 195 This is the Git native format and is `<time> SP <offutc>`. 196 It is also fast-import's default format, if \--date-format was 197 not specified. 198+ 199The time of the event is specified by `<time>` as the number of 200seconds since the UNIX epoch (midnight, Jan 1, 1970, UTC) and is 201written as an ASCII decimal integer. 202+ 203The local offset is specified by `<offutc>` as a positive or negative 204offset from UTC. For example EST (which is 5 hours behind UTC) 205would be expressed in `<tz>` by ``-0500'' while UTC is ``+0000''. 206The local offset does not affect `<time>`; it is used only as an 207advisement to help formatting routines display the timestamp. 208+ 209If the local offset is not available in the source material, use 210``+0000'', or the most common local offset. For example many 211organizations have a CVS repository which has only ever been accessed 212by users who are located in the same location and timezone. In this 213case a reasonable offset from UTC could be assumed. 214+ 215Unlike the `rfc2822` format, this format is very strict. Any 216variation in formatting will cause fast-import to reject the value. 217 218`rfc2822`:: 219 This is the standard email format as described by RFC 2822. 220+ 221An example value is ``Tue Feb 6 11:22:18 2007 -0500''. The Git 222parser is accurate, but a little on the lenient side. It is the 223same parser used by 'git-am' when applying patches 224received from email. 225+ 226Some malformed strings may be accepted as valid dates. In some of 227these cases Git will still be able to obtain the correct date from 228the malformed string. There are also some types of malformed 229strings which Git will parse wrong, and yet consider valid. 230Seriously malformed strings will be rejected. 231+ 232Unlike the `raw` format above, the timezone/UTC offset information 233contained in an RFC 2822 date string is used to adjust the date 234value to UTC prior to storage. Therefore it is important that 235this information be as accurate as possible. 236+ 237If the source material uses RFC 2822 style dates, 238the frontend should let fast-import handle the parsing and conversion 239(rather than attempting to do it itself) as the Git parser has 240been well tested in the wild. 241+ 242Frontends should prefer the `raw` format if the source material 243already uses UNIX-epoch format, can be coaxed to give dates in that 244format, or its format is easily convertible to it, as there is no 245ambiguity in parsing. 246 247`now`:: 248 Always use the current time and timezone. The literal 249 `now` must always be supplied for `<when>`. 250+ 251This is a toy format. The current time and timezone of this system 252is always copied into the identity string at the time it is being 253created by fast-import. There is no way to specify a different time or 254timezone. 255+ 256This particular format is supplied as its short to implement and 257may be useful to a process that wants to create a new commit 258right now, without needing to use a working directory or 259'git-update-index'. 260+ 261If separate `author` and `committer` commands are used in a `commit` 262the timestamps may not match, as the system clock will be polled 263twice (once for each command). The only way to ensure that both 264author and committer identity information has the same timestamp 265is to omit `author` (thus copying from `committer`) or to use a 266date format other than `now`. 267 268Commands 269~~~~~~~~ 270fast-import accepts several commands to update the current repository 271and 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`:: 296 Forces fast-import to close the current packfile, generate its 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. 300 301`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. 305 306`commit` 307~~~~~~~~ 308Create or update a branch with a new commit, recording one logical 309change to the project. 310 311.... 312 'commit' SP <ref> LF 313 mark? 314 ('author' SP <name> SP LT <email> GT SP <when> LF)? 315 'committer' SP <name> SP LT <email> GT SP <when> LF 316 data 317 ('from' SP <committish> LF)? 318 ('merge' SP <committish> LF)? 319 (filemodify | filedelete | filecopy | filerename | filedeleteall | notemodify)* 320 LF? 321.... 322 323where `<ref>` is the name of the branch to make the commit on. 324Typically branch names are prefixed with `refs/heads/` in 325Git, 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 328a Git refname, no quoting or escaping syntax is supported here. 329 330A `mark` command may optionally appear, requesting fast-import to save a 331reference to the newly created commit for future use by the frontend 332(see below for format). It is very common for frontends to mark 333every commit they create, thereby allowing future branch creation 334from any imported commit. 335 336The `data` command following `committer` must supply the commit 337message (see below for `data` command syntax). To import an empty 338commit message use a 0 length data. Commit messages are free-form 339and are not interpreted by Git. Currently they must be encoded in 340UTF-8, as fast-import does not permit other encodings to be specified. 341 342Zero or more `filemodify`, `filedelete`, `filecopy`, `filerename`, 343`filedeleteall` and `notemodify` commands 344may be included to update the contents of the branch prior to 345creating the commit. These commands may be supplied in any order. 346However it is recommended that a `filedeleteall` command precede 347all `filemodify`, `filecopy`, `filerename` and `notemodify` commands in 348the same commit, as `filedeleteall` wipes the branch clean (see below). 349 350The `LF` after the command is optional (it used to be required). 351 352`author` 353^^^^^^^^ 354An `author` command may optionally appear, if the author information 355might differ from the committer information. If `author` is omitted 356then fast-import will automatically use the committer's information for 357the author portion of the commit. See below for a description of 358the fields in `author`, as they are identical to `committer`. 359 360`committer` 361^^^^^^^^^^^ 362The `committer` command indicates who made this commit, and when 363they made it. 364 365Here `<name>` is the person's display name (for example 366``Com M Itter'') and `<email>` is the person's email address 367(``cm@example.com''). `LT` and `GT` are the literal less-than (\x3c) 368and greater-than (\x3e) symbols. These are required to delimit 369the email address from the other fields in the line. Note that 370`<name>` is free-form and may contain any sequence of bytes, except 371`LT` and `LF`. It is typically UTF-8 encoded. 372 373The time of the change is specified by `<when>` using the date format 374that was selected by the \--date-format=<fmt> command line option. 375See ``Date Formats'' above for the set of supported formats, and 376their syntax. 377 378`from` 379^^^^^^ 380The `from` command is used to specify the commit to initialize 381this branch from. This revision will be the first ancestor of the 382new commit. 383 384Omitting the `from` command in the first commit of a new branch 385will cause fast-import to create that commit with no ancestor. This 386tends to be desired only for the initial commit of a project. 387If the frontend creates all files from scratch when making a new 388branch, a `merge` command may be used instead of `from` to start 389the commit with an empty tree. 390Omitting the `from` command on existing branches is usually desired, 391as the current commit on that branch is automatically assumed to 392be the first ancestor of the new commit. 393 394As `LF` is not valid in a Git refname or SHA-1 expression, no 395quoting or escaping syntax is supported within `<committish>`. 396 397Here `<committish>` is any of the following: 398 399* The name of an existing branch already in fast-import's internal branch 400 table. If fast-import doesn't know the name, its treated as a SHA-1 401 expression. 402 403* A mark reference, `:<idnum>`, where `<idnum>` is the mark number. 404+ 405The reason fast-import uses `:` to denote a mark reference is this character 406is not legal in a Git branch name. The leading `:` makes it easy 407to distinguish between the mark 42 (`:42`) and the branch 42 (`42` 408or `refs/heads/42`), or an abbreviated SHA-1 which happened to 409consist only of base-10 digits. 410+ 411Marks must be declared (via `mark`) before they can be used. 412 413* A complete 40 byte or abbreviated commit SHA-1 in hex. 414 415* Any valid Git SHA-1 expression that resolves to a commit. See 416 ``SPECIFYING REVISIONS'' in linkgit:git-rev-parse[1] for details. 417 418The special case of restarting an incremental import from the 419current branch value should be written as: 420---- 421 from refs/heads/branch^0 422---- 423The `{caret}0` suffix is necessary as fast-import does not permit a branch to 424start from itself, and the branch is created in memory before the 425`from` command is even read from the input. Adding `{caret}0` will force 426fast-import to resolve the commit through Git's revision parsing library, 427rather than its internal branch table, thereby loading in the 428existing value of the branch. 429 430`merge` 431^^^^^^^ 432Includes one additional ancestor commit. If the `from` command is 433omitted when creating a new branch, the first `merge` commit will be 434the first ancestor of the current commit, and the branch will start 435out with no files. An unlimited number of `merge` commands per 436commit are permitted by fast-import, thereby establishing an n-way merge. 437However Git's other tools never create commits with more than 15 438additional ancestors (forming a 16-way merge). For this reason 439it is suggested that frontends do not use more than 15 `merge` 440commands per commit; 16, if starting a new, empty branch. 441 442Here `<committish>` is any of the commit specification expressions 443also accepted by `from` (see above). 444 445`filemodify` 446^^^^^^^^^^^^ 447Included in a `commit` command to add a new file or change the 448content of an existing file. This command has two different means 449of specifying the content of the file. 450 451External data format:: 452 The data content for the file was already supplied by a prior 453 `blob` command. The frontend just needs to connect it. 454+ 455.... 456 'M' SP <mode> SP <dataref> SP <path> LF 457.... 458+ 459Here `<dataref>` can be either a mark reference (`:<idnum>`) 460set by a prior `blob` command, or a full 40-byte SHA-1 of an 461existing Git blob object. 462 463Inline data format:: 464 The data content for the file has not been supplied yet. 465 The frontend wants to supply it as part of this modify 466 command. 467+ 468.... 469 'M' SP <mode> SP 'inline' SP <path> LF 470 data 471.... 472+ 473See below for a detailed description of the `data` command. 474 475In both formats `<mode>` is the type of file entry, specified 476in octal. Git only supports the following modes: 477 478* `100644` or `644`: A normal (not-executable) file. The majority 479 of files in most projects use this mode. If in doubt, this is 480 what you want. 481* `100755` or `755`: A normal, but executable, file. 482* `120000`: A symlink, the content of the file will be the link target. 483* `160000`: A gitlink, SHA-1 of the object refers to a commit in 484 another repository. Git links can only be specified by SHA or through 485 a commit mark. They are used to implement submodules. 486 487In both formats `<path>` is the complete path of the file to be added 488(if not already existing) or modified (if already existing). 489 490A `<path>` string must use UNIX-style directory separators (forward 491slash `/`), may contain any byte other than `LF`, and must not 492start with double quote (`"`). 493 494If an `LF` or double quote must be encoded into `<path>` shell-style 495quoting should be used, e.g. `"path/with\n and \" in it"`. 496 497The value of `<path>` must be in canonical form. That is it must not: 498 499* contain an empty directory component (e.g. `foo//bar` is invalid), 500* end with a directory separator (e.g. `foo/` is invalid), 501* start with a directory separator (e.g. `/foo` is invalid), 502* contain the special component `.` or `..` (e.g. `foo/./bar` and 503 `foo/../bar` are invalid). 504 505It is recommended that `<path>` always be encoded using UTF-8. 506 507`filedelete` 508^^^^^^^^^^^^ 509Included in a `commit` command to remove a file or recursively 510delete an entire directory from the branch. If the file or directory 511removal makes its parent directory empty, the parent directory will 512be automatically removed too. This cascades up the tree until the 513first non-empty directory or the root is reached. 514 515.... 516 'D' SP <path> LF 517.... 518 519here `<path>` is the complete path of the file or subdirectory to 520be removed from the branch. 521See `filemodify` above for a detailed description of `<path>`. 522 523`filecopy` 524^^^^^^^^^^^^ 525Recursively copies an existing file or subdirectory to a different 526location within the branch. The existing file or directory must 527exist. If the destination exists it will be completely replaced 528by the content copied from the source. 529 530.... 531 'C' SP <path> SP <path> LF 532.... 533 534here the first `<path>` is the source location and the second 535`<path>` is the destination. See `filemodify` above for a detailed 536description of what `<path>` may look like. To use a source path 537that contains SP the path must be quoted. 538 539A `filecopy` command takes effect immediately. Once the source 540location has been copied to the destination any future commands 541applied to the source location will not impact the destination of 542the copy. 543 544`filerename` 545^^^^^^^^^^^^ 546Renames an existing file or subdirectory to a different location 547within the branch. The existing file or directory must exist. If 548the destination exists it will be replaced by the source directory. 549 550.... 551 'R' SP <path> SP <path> LF 552.... 553 554here the first `<path>` is the source location and the second 555`<path>` is the destination. See `filemodify` above for a detailed 556description of what `<path>` may look like. To use a source path 557that contains SP the path must be quoted. 558 559A `filerename` command takes effect immediately. Once the source 560location has been renamed to the destination any future commands 561applied to the source location will create new files there and not 562impact the destination of the rename. 563 564Note that a `filerename` is the same as a `filecopy` followed by a 565`filedelete` of the source location. There is a slight performance 566advantage to using `filerename`, but the advantage is so small 567that it is never worth trying to convert a delete/add pair in 568source material into a rename for fast-import. This `filerename` 569command is provided just to simplify frontends that already have 570rename information and don't want bother with decomposing it into a 571`filecopy` followed by a `filedelete`. 572 573`filedeleteall` 574^^^^^^^^^^^^^^^ 575Included in a `commit` command to remove all files (and also all 576directories) from the branch. This command resets the internal 577branch structure to have no files in it, allowing the frontend 578to subsequently add all interesting files from scratch. 579 580.... 581 'deleteall' LF 582.... 583 584This command is extremely useful if the frontend does not know 585(or does not care to know) what files are currently on the branch, 586and therefore cannot generate the proper `filedelete` commands to 587update the content. 588 589Issuing a `filedeleteall` followed by the needed `filemodify` 590commands to set the correct content will produce the same results 591as sending only the needed `filemodify` and `filedelete` commands. 592The `filedeleteall` approach may however require fast-import to use slightly 593more memory per active branch (less than 1 MiB for even most large 594projects); so frontends that can easily obtain only the affected 595paths for a commit are encouraged to do so. 596 597`notemodify` 598^^^^^^^^^^^^ 599Included in a `commit` command to add a new note (annotating a given 600commit) or change the content of an existing note. This command has 601two different means of specifying the content of the note. 602 603External data format:: 604 The data content for the note was already supplied by a prior 605 `blob` command. The frontend just needs to connect it to the 606 commit that is to be annotated. 607+ 608.... 609 'N' SP <dataref> SP <committish> LF 610.... 611+ 612Here `<dataref>` can be either a mark reference (`:<idnum>`) 613set by a prior `blob` command, or a full 40-byte SHA-1 of an 614existing Git blob object. 615 616Inline data format:: 617 The data content for the note has not been supplied yet. 618 The frontend wants to supply it as part of this modify 619 command. 620+ 621.... 622 'N' SP 'inline' SP <committish> LF 623 data 624.... 625+ 626See below for a detailed description of the `data` command. 627 628In both formats `<committish>` is any of the commit specification 629expressions also accepted by `from` (see above). 630 631`mark` 632~~~~~~ 633Arranges for fast-import to save a reference to the current object, allowing 634the frontend to recall this object at a future point in time, without 635knowing its SHA-1. Here the current object is the object creation 636command the `mark` command appears within. This can be `commit`, 637`tag`, and `blob`, but `commit` is the most common usage. 638 639.... 640 'mark' SP ':' <idnum> LF 641.... 642 643where `<idnum>` is the number assigned by the frontend to this mark. 644The value of `<idnum>` is expressed as an ASCII decimal integer. 645The value 0 is reserved and cannot be used as 646a mark. Only values greater than or equal to 1 may be used as marks. 647 648New marks are created automatically. Existing marks can be moved 649to another object simply by reusing the same `<idnum>` in another 650`mark` command. 651 652`tag` 653~~~~~ 654Creates an annotated tag referring to a specific commit. To create 655lightweight (non-annotated) tags see the `reset` command below. 656 657.... 658 'tag' SP <name> LF 659 'from' SP <committish> LF 660 'tagger' SP <name> SP LT <email> GT SP <when> LF 661 data 662.... 663 664where `<name>` is the name of the tag to create. 665 666Tag names are automatically prefixed with `refs/tags/` when stored 667in Git, so importing the CVS branch symbol `RELENG-1_0-FINAL` would 668use just `RELENG-1_0-FINAL` for `<name>`, and fast-import will write the 669corresponding ref as `refs/tags/RELENG-1_0-FINAL`. 670 671The value of `<name>` must be a valid refname in Git and therefore 672may contain forward slashes. As `LF` is not valid in a Git refname, 673no quoting or escaping syntax is supported here. 674 675The `from` command is the same as in the `commit` command; see 676above for details. 677 678The `tagger` command uses the same format as `committer` within 679`commit`; again see above for details. 680 681The `data` command following `tagger` must supply the annotated tag 682message (see below for `data` command syntax). To import an empty 683tag message use a 0 length data. Tag messages are free-form and are 684not interpreted by Git. Currently they must be encoded in UTF-8, 685as fast-import does not permit other encodings to be specified. 686 687Signing annotated tags during import from within fast-import is not 688supported. Trying to include your own PGP/GPG signature is not 689recommended, as the frontend does not (easily) have access to the 690complete set of bytes which normally goes into such a signature. 691If signing is required, create lightweight tags from within fast-import with 692`reset`, then create the annotated versions of those tags offline 693with the standard 'git-tag' process. 694 695`reset` 696~~~~~~~ 697Creates (or recreates) the named branch, optionally starting from 698a specific revision. The reset command allows a frontend to issue 699a new `from` command for an existing branch, or to create a new 700branch from an existing commit without creating a new commit. 701 702.... 703 'reset' SP <ref> LF 704 ('from' SP <committish> LF)? 705 LF? 706.... 707 708For a detailed description of `<ref>` and `<committish>` see above 709under `commit` and `from`. 710 711The `LF` after the command is optional (it used to be required). 712 713The `reset` command can also be used to create lightweight 714(non-annotated) tags. For example: 715 716==== 717 reset refs/tags/938 718 from :938 719==== 720 721would create the lightweight tag `refs/tags/938` referring to 722whatever commit mark `:938` references. 723 724`blob` 725~~~~~~ 726Requests writing one file revision to the packfile. The revision 727is not connected to any commit; this connection must be formed in 728a subsequent `commit` command by referencing the blob through an 729assigned mark. 730 731.... 732 'blob' LF 733 mark? 734 data 735.... 736 737The mark command is optional here as some frontends have chosen 738to generate the Git SHA-1 for the blob on their own, and feed that 739directly to `commit`. This is typically more work than its worth 740however, as marks are inexpensive to store and easy to use. 741 742`data` 743~~~~~~ 744Supplies raw data (for use as blob/file content, commit messages, or 745annotated tag messages) to fast-import. Data can be supplied using an exact 746byte count or delimited with a terminating line. Real frontends 747intended for production-quality conversions should always use the 748exact byte count format, as it is more robust and performs better. 749The delimited format is intended primarily for testing fast-import. 750 751Comment lines appearing within the `<raw>` part of `data` commands 752are always taken to be part of the body of the data and are therefore 753never ignored by fast-import. This makes it safe to import any 754file/message content whose lines might start with `#`. 755 756Exact byte count format:: 757 The frontend must specify the number of bytes of data. 758+ 759.... 760 'data' SP <count> LF 761 <raw> LF? 762.... 763+ 764where `<count>` is the exact number of bytes appearing within 765`<raw>`. The value of `<count>` is expressed as an ASCII decimal 766integer. The `LF` on either side of `<raw>` is not 767included in `<count>` and will not be included in the imported data. 768+ 769The `LF` after `<raw>` is optional (it used to be required) but 770recommended. Always including it makes debugging a fast-import 771stream easier as the next command always starts in column 0 772of the next line, even if `<raw>` did not end with an `LF`. 773 774Delimited format:: 775 A delimiter string is used to mark the end of the data. 776 fast-import will compute the length by searching for the delimiter. 777 This format is primarily useful for testing and is not 778 recommended for real data. 779+ 780.... 781 'data' SP '<<' <delim> LF 782 <raw> LF 783 <delim> LF 784 LF? 785.... 786+ 787where `<delim>` is the chosen delimiter string. The string `<delim>` 788must not appear on a line by itself within `<raw>`, as otherwise 789fast-import will think the data ends earlier than it really does. The `LF` 790immediately trailing `<raw>` is part of `<raw>`. This is one of 791the limitations of the delimited format, it is impossible to supply 792a data chunk which does not have an LF as its last byte. 793+ 794The `LF` after `<delim> LF` is optional (it used to be required). 795 796`checkpoint` 797~~~~~~~~~~~~ 798Forces fast-import to close the current packfile, start a new one, and to 799save out all current branch refs, tags and marks. 800 801.... 802 'checkpoint' LF 803 LF? 804.... 805 806Note that fast-import automatically switches packfiles when the current 807packfile reaches \--max-pack-size, or 4 GiB, whichever limit is 808smaller. During an automatic packfile switch fast-import does not update 809the branch refs, tags or marks. 810 811As a `checkpoint` can require a significant amount of CPU time and 812disk IO (to compute the overall pack SHA-1 checksum, generate the 813corresponding index file, and update the refs) it can easily take 814several minutes for a single `checkpoint` command to complete. 815 816Frontends may choose to issue checkpoints during extremely large 817and long running imports, or when they need to allow another Git 818process access to a branch. However given that a 30 GiB Subversion 819repository can be loaded into Git through fast-import in about 3 hours, 820explicit checkpointing may not be necessary. 821 822The `LF` after the command is optional (it used to be required). 823 824`progress` 825~~~~~~~~~~ 826Causes fast-import to print the entire `progress` line unmodified to 827its standard output channel (file descriptor 1) when the command is 828processed from the input stream. The command otherwise has no impact 829on the current import, or on any of fast-import's internal state. 830 831.... 832 'progress' SP <any> LF 833 LF? 834.... 835 836The `<any>` part of the command may contain any sequence of bytes 837that does not contain `LF`. The `LF` after the command is optional. 838Callers may wish to process the output through a tool such as sed to 839remove the leading part of the line, for example: 840 841==== 842 frontend | git fast-import | sed 's/^progress //' 843==== 844 845Placing a `progress` command immediately after a `checkpoint` will 846inform the reader when the `checkpoint` has been completed and it 847can safely access the refs that fast-import updated. 848 849Crash Reports 850------------- 851If fast-import is supplied invalid input it will terminate with a 852non-zero exit status and create a crash report in the top level of 853the Git repository it was importing into. Crash reports contain 854a snapshot of the internal fast-import state as well as the most 855recent commands that lead up to the crash. 856 857All recent commands (including stream comments, file changes and 858progress commands) are shown in the command history within the crash 859report, but raw file data and commit messages are excluded from the 860crash report. This exclusion saves space within the report file 861and reduces the amount of buffering that fast-import must perform 862during execution. 863 864After writing a crash report fast-import will close the current 865packfile and export the marks table. This allows the frontend 866developer to inspect the repository state and resume the import from 867the point where it crashed. The modified branches and tags are not 868updated during a crash, as the import did not complete successfully. 869Branch and tag information can be found in the crash report and 870must be applied manually if the update is needed. 871 872An example crash: 873 874==== 875 $ cat >in <<END_OF_INPUT 876 # my very first test commit 877 commit refs/heads/master 878 committer Shawn O. Pearce <spearce> 19283 -0400 879 # who is that guy anyway? 880 data <<EOF 881 this is my commit 882 EOF 883 M 644 inline .gitignore 884 data <<EOF 885 .gitignore 886 EOF 887 M 777 inline bob 888 END_OF_INPUT 889 890 $ git fast-import <in 891 fatal: Corrupt mode: M 777 inline bob 892 fast-import: dumping crash report to .git/fast_import_crash_8434 893 894 $ cat .git/fast_import_crash_8434 895 fast-import crash report: 896 fast-import process: 8434 897 parent process : 1391 898 at Sat Sep 1 00:58:12 2007 899 900 fatal: Corrupt mode: M 777 inline bob 901 902 Most Recent Commands Before Crash 903 --------------------------------- 904 # my very first test commit 905 commit refs/heads/master 906 committer Shawn O. Pearce <spearce> 19283 -0400 907 # who is that guy anyway? 908 data <<EOF 909 M 644 inline .gitignore 910 data <<EOF 911 * M 777 inline bob 912 913 Active Branch LRU 914 ----------------- 915 active_branches = 1 cur, 5 max 916 917 pos clock name 918 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 919 1) 0 refs/heads/master 920 921 Inactive Branches 922 ----------------- 923 refs/heads/master: 924 status : active loaded dirty 925 tip commit : 0000000000000000000000000000000000000000 926 old tree : 0000000000000000000000000000000000000000 927 cur tree : 0000000000000000000000000000000000000000 928 commit clock: 0 929 last pack : 930 931 932 ------------------- 933 END OF CRASH REPORT 934==== 935 936Tips and Tricks 937--------------- 938The following tips and tricks have been collected from various 939users of fast-import, and are offered here as suggestions. 940 941Use One Mark Per Commit 942~~~~~~~~~~~~~~~~~~~~~~~ 943When doing a repository conversion, use a unique mark per commit 944(`mark :<n>`) and supply the \--export-marks option on the command 945line. fast-import will dump a file which lists every mark and the Git 946object SHA-1 that corresponds to it. If the frontend can tie 947the marks back to the source repository, it is easy to verify the 948accuracy and completeness of the import by comparing each Git 949commit to the corresponding source revision. 950 951Coming from a system such as Perforce or Subversion this should be 952quite simple, as the fast-import mark can also be the Perforce changeset 953number or the Subversion revision number. 954 955Freely Skip Around Branches 956~~~~~~~~~~~~~~~~~~~~~~~~~~~ 957Don't bother trying to optimize the frontend to stick to one branch 958at a time during an import. Although doing so might be slightly 959faster for fast-import, it tends to increase the complexity of the frontend 960code considerably. 961 962The branch LRU builtin to fast-import tends to behave very well, and the 963cost of activating an inactive branch is so low that bouncing around 964between branches has virtually no impact on import performance. 965 966Handling Renames 967~~~~~~~~~~~~~~~~ 968When importing a renamed file or directory, simply delete the old 969name(s) and modify the new name(s) during the corresponding commit. 970Git performs rename detection after-the-fact, rather than explicitly 971during a commit. 972 973Use Tag Fixup Branches 974~~~~~~~~~~~~~~~~~~~~~~ 975Some other SCM systems let the user create a tag from multiple 976files which are not from the same commit/changeset. Or to create 977tags which are a subset of the files available in the repository. 978 979Importing these tags as-is in Git is impossible without making at 980least one commit which ``fixes up'' the files to match the content 981of the tag. Use fast-import's `reset` command to reset a dummy branch 982outside of your normal branch space to the base commit for the tag, 983then commit one or more file fixup commits, and finally tag the 984dummy branch. 985 986For example since all normal branches are stored under `refs/heads/` 987name the tag fixup branch `TAG_FIXUP`. This way it is impossible for 988the fixup branch used by the importer to have namespace conflicts 989with real branches imported from the source (the name `TAG_FIXUP` 990is not `refs/heads/TAG_FIXUP`). 991 992When committing fixups, consider using `merge` to connect the 993commit(s) which are supplying file revisions to the fixup branch. 994Doing so will allow tools such as 'git-blame' to track 995through the real commit history and properly annotate the source 996files. 997 998After fast-import terminates the frontend will need to do `rm .git/TAG_FIXUP` 999to remove the dummy branch.10001001Import Now, Repack Later1002~~~~~~~~~~~~~~~~~~~~~~~~1003As soon as fast-import completes the Git repository is completely valid1004and ready for use. Typically this takes only a very short time,1005even for considerably large projects (100,000+ commits).10061007However repacking the repository is necessary to improve data1008locality and access performance. It can also take hours on extremely1009large projects (especially if -f and a large \--window parameter is1010used). Since repacking is safe to run alongside readers and writers,1011run the repack in the background and let it finish when it finishes.1012There is no reason to wait to explore your new Git project!10131014If you choose to wait for the repack, don't try to run benchmarks1015or performance tests until repacking is completed. fast-import outputs1016suboptimal packfiles that are simply never seen in real use1017situations.10181019Repacking Historical Data1020~~~~~~~~~~~~~~~~~~~~~~~~~1021If you are repacking very old imported data (e.g. older than the1022last year), consider expending some extra CPU time and supplying1023\--window=50 (or higher) when you run 'git-repack'.1024This will take longer, but will also produce a smaller packfile.1025You only need to expend the effort once, and everyone using your1026project will benefit from the smaller repository.10271028Include Some Progress Messages1029~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~1030Every once in a while have your frontend emit a `progress` message1031to fast-import. The contents of the messages are entirely free-form,1032so one suggestion would be to output the current month and year1033each time the current commit date moves into the next month.1034Your users will feel better knowing how much of the data stream1035has been processed.103610371038Packfile Optimization1039---------------------1040When packing a blob fast-import always attempts to deltify against the last1041blob written. Unless specifically arranged for by the frontend,1042this will probably not be a prior version of the same file, so the1043generated delta will not be the smallest possible. The resulting1044packfile will be compressed, but will not be optimal.10451046Frontends which have efficient access to all revisions of a1047single file (for example reading an RCS/CVS ,v file) can choose1048to supply all revisions of that file as a sequence of consecutive1049`blob` commands. This allows fast-import to deltify the different file1050revisions against each other, saving space in the final packfile.1051Marks can be used to later identify individual file revisions during1052a sequence of `commit` commands.10531054The packfile(s) created by fast-import do not encourage good disk access1055patterns. This is caused by fast-import writing the data in the order1056it is received on standard input, while Git typically organizes1057data within packfiles to make the most recent (current tip) data1058appear before historical data. Git also clusters commits together,1059speeding up revision traversal through better cache locality.10601061For this reason it is strongly recommended that users repack the1062repository with `git repack -a -d` after fast-import completes, allowing1063Git to reorganize the packfiles for faster data access. If blob1064deltas are suboptimal (see above) then also adding the `-f` option1065to force recomputation of all deltas can significantly reduce the1066final packfile size (30-50% smaller can be quite typical).106710681069Memory Utilization1070------------------1071There are a number of factors which affect how much memory fast-import1072requires to perform an import. Like critical sections of core1073Git, fast-import uses its own memory allocators to amortize any overheads1074associated with malloc. In practice fast-import tends to amortize any1075malloc overheads to 0, due to its use of large block allocations.10761077per object1078~~~~~~~~~~1079fast-import maintains an in-memory structure for every object written in1080this execution. On a 32 bit system the structure is 32 bytes,1081on a 64 bit system the structure is 40 bytes (due to the larger1082pointer sizes). Objects in the table are not deallocated until1083fast-import terminates. Importing 2 million objects on a 32 bit system1084will require approximately 64 MiB of memory.10851086The object table is actually a hashtable keyed on the object name1087(the unique SHA-1). This storage configuration allows fast-import to reuse1088an existing or already written object and avoid writing duplicates1089to the output packfile. Duplicate blobs are surprisingly common1090in an import, typically due to branch merges in the source.10911092per mark1093~~~~~~~~1094Marks are stored in a sparse array, using 1 pointer (4 bytes or 81095bytes, depending on pointer size) per mark. Although the array1096is sparse, frontends are still strongly encouraged to use marks1097between 1 and n, where n is the total number of marks required for1098this import.10991100per branch1101~~~~~~~~~~1102Branches are classified as active and inactive. The memory usage1103of the two classes is significantly different.11041105Inactive branches are stored in a structure which uses 96 or 1201106bytes (32 bit or 64 bit systems, respectively), plus the length of1107the branch name (typically under 200 bytes), per branch. fast-import will1108easily handle as many as 10,000 inactive branches in under 2 MiB1109of memory.11101111Active branches have the same overhead as inactive branches, but1112also contain copies of every tree that has been recently modified on1113that branch. If subtree `include` has not been modified since the1114branch became active, its contents will not be loaded into memory,1115but if subtree `src` has been modified by a commit since the branch1116became active, then its contents will be loaded in memory.11171118As active branches store metadata about the files contained on that1119branch, their in-memory storage size can grow to a considerable size1120(see below).11211122fast-import automatically moves active branches to inactive status based on1123a simple least-recently-used algorithm. The LRU chain is updated on1124each `commit` command. The maximum number of active branches can be1125increased or decreased on the command line with \--active-branches=.11261127per active tree1128~~~~~~~~~~~~~~~1129Trees (aka directories) use just 12 bytes of memory on top of the1130memory required for their entries (see ``per active file'' below).1131The cost of a tree is virtually 0, as its overhead amortizes out1132over the individual file entries.11331134per active file entry1135~~~~~~~~~~~~~~~~~~~~~1136Files (and pointers to subtrees) within active trees require 52 or 641137bytes (32/64 bit platforms) per entry. To conserve space, file and1138tree names are pooled in a common string table, allowing the filename1139``Makefile'' to use just 16 bytes (after including the string header1140overhead) no matter how many times it occurs within the project.11411142The active branch LRU, when coupled with the filename string pool1143and lazy loading of subtrees, allows fast-import to efficiently import1144projects with 2,000+ branches and 45,114+ files in a very limited1145memory footprint (less than 2.7 MiB per active branch).114611471148Author1149------1150Written by Shawn O. Pearce <spearce@spearce.org>.11511152Documentation1153--------------1154Documentation by Shawn O. Pearce <spearce@spearce.org>.11551156GIT1157---1158Part of the linkgit:git[1] suite