1git-fast-import(1) 2================== 3 4NAME 5---- 6git-fast-import - Backend for fast Git data importers 7 8 9SYNOPSIS 10-------- 11[verse] 12frontend | 'git fast-import' [<options>] 13 14DESCRIPTION 15----------- 16This program is usually not what the end user wants to run directly. 17Most end users want to use one of the existing frontend programs, 18which parses a specific type of foreign source and feeds the contents 19stored there to 'git fast-import'. 20 21fast-import reads a mixed command/data stream from standard input and 22writes one or more packfiles directly into the current repository. 23When EOF is received on standard input, fast import writes out 24updated branch and tag refs, fully updating the current repository 25with the newly imported data. 26 27The fast-import backend itself can import into an empty repository (one that 28has already been initialized by 'git init') or incrementally 29update an existing populated repository. Whether or not incremental 30imports are supported from a particular foreign source depends on 31the frontend program in use. 32 33 34OPTIONS 35------- 36 37--force:: 38 Force updating modified existing branches, even if doing 39 so would cause commits to be lost (as the new commit does 40 not contain the old commit). 41 42--quiet:: 43 Disable the output shown by --stats, making fast-import usually 44 be silent when it is successful. However, if the import stream 45 has directives intended to show user output (e.g. `progress` 46 directives), the corresponding messages will still be shown. 47 48--stats:: 49 Display some basic statistics about the objects fast-import has 50 created, the packfiles they were stored into, and the 51 memory used by fast-import during this run. Showing this output 52 is currently the default, but can be disabled with --quiet. 53 54Options for Frontends 55~~~~~~~~~~~~~~~~~~~~~ 56 57--cat-blob-fd=<fd>:: 58 Write responses to `get-mark`, `cat-blob`, and `ls` queries to the 59 file descriptor <fd> instead of `stdout`. Allows `progress` 60 output intended for the end-user to be separated from other 61 output. 62 63--date-format=<fmt>:: 64 Specify the type of dates the frontend will supply to 65 fast-import within `author`, `committer` and `tagger` commands. 66 See ``Date Formats'' below for details about which formats 67 are supported, and their syntax. 68 69--done:: 70 Terminate with error if there is no `done` command at the end of 71 the stream. This option might be useful for detecting errors 72 that cause the frontend to terminate before it has started to 73 write a stream. 74 75Locations of Marks Files 76~~~~~~~~~~~~~~~~~~~~~~~~ 77 78--export-marks=<file>:: 79 Dumps the internal marks table to <file> when complete. 80 Marks are written one per line as `:markid SHA-1`. 81 Frontends can use this file to validate imports after they 82 have been completed, or to save the marks table across 83 incremental runs. As <file> is only opened and truncated 84 at checkpoint (or completion) the same path can also be 85 safely given to --import-marks. 86 87--import-marks=<file>:: 88 Before processing any input, load the marks specified in 89 <file>. The input file must exist, must be readable, and 90 must use the same format as produced by --export-marks. 91 Multiple options may be supplied to import more than one 92 set of marks. If a mark is defined to different values, 93 the last file wins. 94 95--import-marks-if-exists=<file>:: 96 Like --import-marks but instead of erroring out, silently 97 skips the file if it does not exist. 98 99--[no-]relative-marks:: 100 After specifying --relative-marks the paths specified 101 with --import-marks= and --export-marks= are relative 102 to an internal directory in the current repository. 103 In git-fast-import this means that the paths are relative 104 to the .git/info/fast-import directory. However, other 105 importers may use a different location. 106+ 107Relative and non-relative marks may be combined by interweaving 108--(no-)-relative-marks with the --(import|export)-marks= options. 109 110Performance and Compression Tuning 111~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 112 113--active-branches=<n>:: 114 Maximum number of branches to maintain active at once. 115 See ``Memory Utilization'' below for details. Default is 5. 116 117--big-file-threshold=<n>:: 118 Maximum size of a blob that fast-import will attempt to 119 create a delta for, expressed in bytes. The default is 512m 120 (512 MiB). Some importers may wish to lower this on systems 121 with constrained memory. 122 123--depth=<n>:: 124 Maximum delta depth, for blob and tree deltification. 125 Default is 50. 126 127--export-pack-edges=<file>:: 128 After creating a packfile, print a line of data to 129 <file> listing the filename of the packfile and the last 130 commit on each branch that was written to that packfile. 131 This information may be useful after importing projects 132 whose total object set exceeds the 4 GiB packfile limit, 133 as these commits can be used as edge points during calls 134 to 'git pack-objects'. 135 136--max-pack-size=<n>:: 137 Maximum size of each output packfile. 138 The default is unlimited. 139 140fastimport.unpackLimit:: 141 See linkgit:git-config[1] 142 143PERFORMANCE 144----------- 145The design of fast-import allows it to import large projects in a minimum 146amount of memory usage and processing time. Assuming the frontend 147is able to keep up with fast-import and feed it a constant stream of data, 148import times for projects holding 10+ years of history and containing 149100,000+ individual commits are generally completed in just 1-2 150hours on quite modest (~$2,000 USD) hardware. 151 152Most bottlenecks appear to be in foreign source data access (the 153source just cannot extract revisions fast enough) or disk IO (fast-import 154writes as fast as the disk will take the data). Imports will run 155faster if the source data is stored on a different drive than the 156destination Git repository (due to less IO contention). 157 158 159DEVELOPMENT COST 160---------------- 161A typical frontend for fast-import tends to weigh in at approximately 200 162lines of Perl/Python/Ruby code. Most developers have been able to 163create working importers in just a couple of hours, even though it 164is their first exposure to fast-import, and sometimes even to Git. This is 165an ideal situation, given that most conversion tools are throw-away 166(use once, and never look back). 167 168 169PARALLEL OPERATION 170------------------ 171Like 'git push' or 'git fetch', imports handled by fast-import are safe to 172run alongside parallel `git repack -a -d` or `git gc` invocations, 173or any other Git operation (including 'git prune', as loose objects 174are never used by fast-import). 175 176fast-import does not lock the branch or tag refs it is actively importing. 177After the import, during its ref update phase, fast-import tests each 178existing branch ref to verify the update will be a fast-forward 179update (the commit stored in the ref is contained in the new 180history of the commit to be written). If the update is not a 181fast-forward update, fast-import will skip updating that ref and instead 182prints a warning message. fast-import will always attempt to update all 183branch refs, and does not stop on the first failure. 184 185Branch updates can be forced with --force, but it's recommended that 186this only be used on an otherwise quiet repository. Using --force 187is not necessary for an initial import into an empty repository. 188 189 190TECHNICAL DISCUSSION 191-------------------- 192fast-import tracks a set of branches in memory. Any branch can be created 193or modified at any point during the import process by sending a 194`commit` command on the input stream. This design allows a frontend 195program to process an unlimited number of branches simultaneously, 196generating commits in the order they are available from the source 197data. It also simplifies the frontend programs considerably. 198 199fast-import does not use or alter the current working directory, or any 200file within it. (It does however update the current Git repository, 201as referenced by `GIT_DIR`.) Therefore an import frontend may use 202the working directory for its own purposes, such as extracting file 203revisions from the foreign source. This ignorance of the working 204directory also allows fast-import to run very quickly, as it does not 205need to perform any costly file update operations when switching 206between branches. 207 208INPUT FORMAT 209------------ 210With the exception of raw file data (which Git does not interpret) 211the fast-import input format is text (ASCII) based. This text based 212format simplifies development and debugging of frontend programs, 213especially when a higher level language such as Perl, Python or 214Ruby is being used. 215 216fast-import is very strict about its input. Where we say SP below we mean 217*exactly* one space. Likewise LF means one (and only one) linefeed 218and HT one (and only one) horizontal tab. 219Supplying additional whitespace characters will cause unexpected 220results, such as branch names or file names with leading or trailing 221spaces in their name, or early termination of fast-import when it encounters 222unexpected input. 223 224Stream Comments 225~~~~~~~~~~~~~~~ 226To aid in debugging frontends fast-import ignores any line that 227begins with `#` (ASCII pound/hash) up to and including the line 228ending `LF`. A comment line may contain any sequence of bytes 229that does not contain an LF and therefore may be used to include 230any detailed debugging information that might be specific to the 231frontend and useful when inspecting a fast-import data stream. 232 233Date Formats 234~~~~~~~~~~~~ 235The following date formats are supported. A frontend should select 236the format it will use for this import by passing the format name 237in the --date-format=<fmt> command-line option. 238 239`raw`:: 240 This is the Git native format and is `<time> SP <offutc>`. 241 It is also fast-import's default format, if --date-format was 242 not specified. 243+ 244The time of the event is specified by `<time>` as the number of 245seconds since the UNIX epoch (midnight, Jan 1, 1970, UTC) and is 246written as an ASCII decimal integer. 247+ 248The local offset is specified by `<offutc>` as a positive or negative 249offset from UTC. For example EST (which is 5 hours behind UTC) 250would be expressed in `<tz>` by ``-0500'' while UTC is ``+0000''. 251The local offset does not affect `<time>`; it is used only as an 252advisement to help formatting routines display the timestamp. 253+ 254If the local offset is not available in the source material, use 255``+0000'', or the most common local offset. For example many 256organizations have a CVS repository which has only ever been accessed 257by users who are located in the same location and time zone. In this 258case a reasonable offset from UTC could be assumed. 259+ 260Unlike the `rfc2822` format, this format is very strict. Any 261variation in formatting will cause fast-import to reject the value. 262 263`rfc2822`:: 264 This is the standard email format as described by RFC 2822. 265+ 266An example value is ``Tue Feb 6 11:22:18 2007 -0500''. The Git 267parser is accurate, but a little on the lenient side. It is the 268same parser used by 'git am' when applying patches 269received from email. 270+ 271Some malformed strings may be accepted as valid dates. In some of 272these cases Git will still be able to obtain the correct date from 273the malformed string. There are also some types of malformed 274strings which Git will parse wrong, and yet consider valid. 275Seriously malformed strings will be rejected. 276+ 277Unlike the `raw` format above, the time zone/UTC offset information 278contained in an RFC 2822 date string is used to adjust the date 279value to UTC prior to storage. Therefore it is important that 280this information be as accurate as possible. 281+ 282If the source material uses RFC 2822 style dates, 283the frontend should let fast-import handle the parsing and conversion 284(rather than attempting to do it itself) as the Git parser has 285been well tested in the wild. 286+ 287Frontends should prefer the `raw` format if the source material 288already uses UNIX-epoch format, can be coaxed to give dates in that 289format, or its format is easily convertible to it, as there is no 290ambiguity in parsing. 291 292`now`:: 293 Always use the current time and time zone. The literal 294 `now` must always be supplied for `<when>`. 295+ 296This is a toy format. The current time and time zone of this system 297is always copied into the identity string at the time it is being 298created by fast-import. There is no way to specify a different time or 299time zone. 300+ 301This particular format is supplied as it's short to implement and 302may be useful to a process that wants to create a new commit 303right now, without needing to use a working directory or 304'git update-index'. 305+ 306If separate `author` and `committer` commands are used in a `commit` 307the timestamps may not match, as the system clock will be polled 308twice (once for each command). The only way to ensure that both 309author and committer identity information has the same timestamp 310is to omit `author` (thus copying from `committer`) or to use a 311date format other than `now`. 312 313Commands 314~~~~~~~~ 315fast-import accepts several commands to update the current repository 316and control the current import process. More detailed discussion 317(with examples) of each command follows later. 318 319`commit`:: 320 Creates a new branch or updates an existing branch by 321 creating a new commit and updating the branch to point at 322 the newly created commit. 323 324`tag`:: 325 Creates an annotated tag object from an existing commit or 326 branch. Lightweight tags are not supported by this command, 327 as they are not recommended for recording meaningful points 328 in time. 329 330`reset`:: 331 Reset an existing branch (or a new branch) to a specific 332 revision. This command must be used to change a branch to 333 a specific revision without making a commit on it. 334 335`blob`:: 336 Convert raw file data into a blob, for future use in a 337 `commit` command. This command is optional and is not 338 needed to perform an import. 339 340`checkpoint`:: 341 Forces fast-import to close the current packfile, generate its 342 unique SHA-1 checksum and index, and start a new packfile. 343 This command is optional and is not needed to perform 344 an import. 345 346`progress`:: 347 Causes fast-import to echo the entire line to its own 348 standard output. This command is optional and is not needed 349 to perform an import. 350 351`done`:: 352 Marks the end of the stream. This command is optional 353 unless the `done` feature was requested using the 354 `--done` command-line option or `feature done` command. 355 356`get-mark`:: 357 Causes fast-import to print the SHA-1 corresponding to a mark 358 to the file descriptor set with `--cat-blob-fd`, or `stdout` if 359 unspecified. 360 361`cat-blob`:: 362 Causes fast-import to print a blob in 'cat-file --batch' 363 format to the file descriptor set with `--cat-blob-fd` or 364 `stdout` if unspecified. 365 366`ls`:: 367 Causes fast-import to print a line describing a directory 368 entry in 'ls-tree' format to the file descriptor set with 369 `--cat-blob-fd` or `stdout` if unspecified. 370 371`feature`:: 372 Enable the specified feature. This requires that fast-import 373 supports the specified feature, and aborts if it does not. 374 375`option`:: 376 Specify any of the options listed under OPTIONS that do not 377 change stream semantic to suit the frontend's needs. This 378 command is optional and is not needed to perform an import. 379 380`commit` 381~~~~~~~~ 382Create or update a branch with a new commit, recording one logical 383change to the project. 384 385.... 386 'commit' SP <ref> LF 387 mark? 388 ('author' (SP <name>)? SP LT <email> GT SP <when> LF)? 389 'committer' (SP <name>)? SP LT <email> GT SP <when> LF 390 data 391 ('from' SP <commit-ish> LF)? 392 ('merge' SP <commit-ish> LF)? 393 (filemodify | filedelete | filecopy | filerename | filedeleteall | notemodify)* 394 LF? 395.... 396 397where `<ref>` is the name of the branch to make the commit on. 398Typically branch names are prefixed with `refs/heads/` in 399Git, so importing the CVS branch symbol `RELENG-1_0` would use 400`refs/heads/RELENG-1_0` for the value of `<ref>`. The value of 401`<ref>` must be a valid refname in Git. As `LF` is not valid in 402a Git refname, no quoting or escaping syntax is supported here. 403 404A `mark` command may optionally appear, requesting fast-import to save a 405reference to the newly created commit for future use by the frontend 406(see below for format). It is very common for frontends to mark 407every commit they create, thereby allowing future branch creation 408from any imported commit. 409 410The `data` command following `committer` must supply the commit 411message (see below for `data` command syntax). To import an empty 412commit message use a 0 length data. Commit messages are free-form 413and are not interpreted by Git. Currently they must be encoded in 414UTF-8, as fast-import does not permit other encodings to be specified. 415 416Zero or more `filemodify`, `filedelete`, `filecopy`, `filerename`, 417`filedeleteall` and `notemodify` commands 418may be included to update the contents of the branch prior to 419creating the commit. These commands may be supplied in any order. 420However it is recommended that a `filedeleteall` command precede 421all `filemodify`, `filecopy`, `filerename` and `notemodify` commands in 422the same commit, as `filedeleteall` wipes the branch clean (see below). 423 424The `LF` after the command is optional (it used to be required). 425 426`author` 427^^^^^^^^ 428An `author` command may optionally appear, if the author information 429might differ from the committer information. If `author` is omitted 430then fast-import will automatically use the committer's information for 431the author portion of the commit. See below for a description of 432the fields in `author`, as they are identical to `committer`. 433 434`committer` 435^^^^^^^^^^^ 436The `committer` command indicates who made this commit, and when 437they made it. 438 439Here `<name>` is the person's display name (for example 440``Com M Itter'') and `<email>` is the person's email address 441(``\cm@example.com''). `LT` and `GT` are the literal less-than (\x3c) 442and greater-than (\x3e) symbols. These are required to delimit 443the email address from the other fields in the line. Note that 444`<name>` and `<email>` are free-form and may contain any sequence 445of bytes, except `LT`, `GT` and `LF`. `<name>` is typically UTF-8 encoded. 446 447The time of the change is specified by `<when>` using the date format 448that was selected by the --date-format=<fmt> command-line option. 449See ``Date Formats'' above for the set of supported formats, and 450their syntax. 451 452`from` 453^^^^^^ 454The `from` command is used to specify the commit to initialize 455this branch from. This revision will be the first ancestor of the 456new commit. The state of the tree built at this commit will begin 457with the state at the `from` commit, and be altered by the content 458modifications in this commit. 459 460Omitting the `from` command in the first commit of a new branch 461will cause fast-import to create that commit with no ancestor. This 462tends to be desired only for the initial commit of a project. 463If the frontend creates all files from scratch when making a new 464branch, a `merge` command may be used instead of `from` to start 465the commit with an empty tree. 466Omitting the `from` command on existing branches is usually desired, 467as the current commit on that branch is automatically assumed to 468be the first ancestor of the new commit. 469 470As `LF` is not valid in a Git refname or SHA-1 expression, no 471quoting or escaping syntax is supported within `<commit-ish>`. 472 473Here `<commit-ish>` is any of the following: 474 475* The name of an existing branch already in fast-import's internal branch 476 table. If fast-import doesn't know the name, it's treated as a SHA-1 477 expression. 478 479* A mark reference, `:<idnum>`, where `<idnum>` is the mark number. 480+ 481The reason fast-import uses `:` to denote a mark reference is this character 482is not legal in a Git branch name. The leading `:` makes it easy 483to distinguish between the mark 42 (`:42`) and the branch 42 (`42` 484or `refs/heads/42`), or an abbreviated SHA-1 which happened to 485consist only of base-10 digits. 486+ 487Marks must be declared (via `mark`) before they can be used. 488 489* A complete 40 byte or abbreviated commit SHA-1 in hex. 490 491* Any valid Git SHA-1 expression that resolves to a commit. See 492 ``SPECIFYING REVISIONS'' in linkgit:gitrevisions[7] for details. 493 494* The special null SHA-1 (40 zeros) specifies that the branch is to be 495 removed. 496 497The special case of restarting an incremental import from the 498current branch value should be written as: 499---- 500 from refs/heads/branch^0 501---- 502The `^0` suffix is necessary as fast-import does not permit a branch to 503start from itself, and the branch is created in memory before the 504`from` command is even read from the input. Adding `^0` will force 505fast-import to resolve the commit through Git's revision parsing library, 506rather than its internal branch table, thereby loading in the 507existing value of the branch. 508 509`merge` 510^^^^^^^ 511Includes one additional ancestor commit. The additional ancestry 512link does not change the way the tree state is built at this commit. 513If the `from` command is 514omitted when creating a new branch, the first `merge` commit will be 515the first ancestor of the current commit, and the branch will start 516out with no files. An unlimited number of `merge` commands per 517commit are permitted by fast-import, thereby establishing an n-way merge. 518 519Here `<commit-ish>` is any of the commit specification expressions 520also accepted by `from` (see above). 521 522`filemodify` 523^^^^^^^^^^^^ 524Included in a `commit` command to add a new file or change the 525content of an existing file. This command has two different means 526of specifying the content of the file. 527 528External data format:: 529 The data content for the file was already supplied by a prior 530 `blob` command. The frontend just needs to connect it. 531+ 532.... 533 'M' SP <mode> SP <dataref> SP <path> LF 534.... 535+ 536Here usually `<dataref>` must be either a mark reference (`:<idnum>`) 537set by a prior `blob` command, or a full 40-byte SHA-1 of an 538existing Git blob object. If `<mode>` is `040000`` then 539`<dataref>` must be the full 40-byte SHA-1 of an existing 540Git tree object or a mark reference set with `--import-marks`. 541 542Inline data format:: 543 The data content for the file has not been supplied yet. 544 The frontend wants to supply it as part of this modify 545 command. 546+ 547.... 548 'M' SP <mode> SP 'inline' SP <path> LF 549 data 550.... 551+ 552See below for a detailed description of the `data` command. 553 554In both formats `<mode>` is the type of file entry, specified 555in octal. Git only supports the following modes: 556 557* `100644` or `644`: A normal (not-executable) file. The majority 558 of files in most projects use this mode. If in doubt, this is 559 what you want. 560* `100755` or `755`: A normal, but executable, file. 561* `120000`: A symlink, the content of the file will be the link target. 562* `160000`: A gitlink, SHA-1 of the object refers to a commit in 563 another repository. Git links can only be specified by SHA or through 564 a commit mark. They are used to implement submodules. 565* `040000`: A subdirectory. Subdirectories can only be specified by 566 SHA or through a tree mark set with `--import-marks`. 567 568In both formats `<path>` is the complete path of the file to be added 569(if not already existing) or modified (if already existing). 570 571A `<path>` string must use UNIX-style directory separators (forward 572slash `/`), may contain any byte other than `LF`, and must not 573start with double quote (`"`). 574 575A path can use C-style string quoting; this is accepted in all cases 576and mandatory if the filename starts with double quote or contains 577`LF`. In C-style quoting, the complete name should be surrounded with 578double quotes, and any `LF`, backslash, or double quote characters 579must be escaped by preceding them with a backslash (e.g., 580`"path/with\n, \\ and \" in it"`). 581 582The value of `<path>` must be in canonical form. That is it must not: 583 584* contain an empty directory component (e.g. `foo//bar` is invalid), 585* end with a directory separator (e.g. `foo/` is invalid), 586* start with a directory separator (e.g. `/foo` is invalid), 587* contain the special component `.` or `..` (e.g. `foo/./bar` and 588 `foo/../bar` are invalid). 589 590The root of the tree can be represented by an empty string as `<path>`. 591 592It is recommended that `<path>` always be encoded using UTF-8. 593 594`filedelete` 595^^^^^^^^^^^^ 596Included in a `commit` command to remove a file or recursively 597delete an entire directory from the branch. If the file or directory 598removal makes its parent directory empty, the parent directory will 599be automatically removed too. This cascades up the tree until the 600first non-empty directory or the root is reached. 601 602.... 603 'D' SP <path> LF 604.... 605 606here `<path>` is the complete path of the file or subdirectory to 607be removed from the branch. 608See `filemodify` above for a detailed description of `<path>`. 609 610`filecopy` 611^^^^^^^^^^ 612Recursively copies an existing file or subdirectory to a different 613location within the branch. The existing file or directory must 614exist. If the destination exists it will be completely replaced 615by the content copied from the source. 616 617.... 618 'C' SP <path> SP <path> LF 619.... 620 621here the first `<path>` is the source location and the second 622`<path>` is the destination. See `filemodify` above for a detailed 623description of what `<path>` may look like. To use a source path 624that contains SP the path must be quoted. 625 626A `filecopy` command takes effect immediately. Once the source 627location has been copied to the destination any future commands 628applied to the source location will not impact the destination of 629the copy. 630 631`filerename` 632^^^^^^^^^^^^ 633Renames an existing file or subdirectory to a different location 634within the branch. The existing file or directory must exist. If 635the destination exists it will be replaced by the source directory. 636 637.... 638 'R' SP <path> SP <path> LF 639.... 640 641here the first `<path>` is the source location and the second 642`<path>` is the destination. See `filemodify` above for a detailed 643description of what `<path>` may look like. To use a source path 644that contains SP the path must be quoted. 645 646A `filerename` command takes effect immediately. Once the source 647location has been renamed to the destination any future commands 648applied to the source location will create new files there and not 649impact the destination of the rename. 650 651Note that a `filerename` is the same as a `filecopy` followed by a 652`filedelete` of the source location. There is a slight performance 653advantage to using `filerename`, but the advantage is so small 654that it is never worth trying to convert a delete/add pair in 655source material into a rename for fast-import. This `filerename` 656command is provided just to simplify frontends that already have 657rename information and don't want bother with decomposing it into a 658`filecopy` followed by a `filedelete`. 659 660`filedeleteall` 661^^^^^^^^^^^^^^^ 662Included in a `commit` command to remove all files (and also all 663directories) from the branch. This command resets the internal 664branch structure to have no files in it, allowing the frontend 665to subsequently add all interesting files from scratch. 666 667.... 668 'deleteall' LF 669.... 670 671This command is extremely useful if the frontend does not know 672(or does not care to know) what files are currently on the branch, 673and therefore cannot generate the proper `filedelete` commands to 674update the content. 675 676Issuing a `filedeleteall` followed by the needed `filemodify` 677commands to set the correct content will produce the same results 678as sending only the needed `filemodify` and `filedelete` commands. 679The `filedeleteall` approach may however require fast-import to use slightly 680more memory per active branch (less than 1 MiB for even most large 681projects); so frontends that can easily obtain only the affected 682paths for a commit are encouraged to do so. 683 684`notemodify` 685^^^^^^^^^^^^ 686Included in a `commit` `<notes_ref>` command to add a new note 687annotating a `<commit-ish>` or change this annotation contents. 688Internally it is similar to filemodify 100644 on `<commit-ish>` 689path (maybe split into subdirectories). It's not advised to 690use any other commands to write to the `<notes_ref>` tree except 691`filedeleteall` to delete all existing notes in this tree. 692This command has two different means of specifying the content 693of the note. 694 695External data format:: 696 The data content for the note was already supplied by a prior 697 `blob` command. The frontend just needs to connect it to the 698 commit that is to be annotated. 699+ 700.... 701 'N' SP <dataref> SP <commit-ish> LF 702.... 703+ 704Here `<dataref>` can be either a mark reference (`:<idnum>`) 705set by a prior `blob` command, or a full 40-byte SHA-1 of an 706existing Git blob object. 707 708Inline data format:: 709 The data content for the note has not been supplied yet. 710 The frontend wants to supply it as part of this modify 711 command. 712+ 713.... 714 'N' SP 'inline' SP <commit-ish> LF 715 data 716.... 717+ 718See below for a detailed description of the `data` command. 719 720In both formats `<commit-ish>` is any of the commit specification 721expressions also accepted by `from` (see above). 722 723`mark` 724~~~~~~ 725Arranges for fast-import to save a reference to the current object, allowing 726the frontend to recall this object at a future point in time, without 727knowing its SHA-1. Here the current object is the object creation 728command the `mark` command appears within. This can be `commit`, 729`tag`, and `blob`, but `commit` is the most common usage. 730 731.... 732 'mark' SP ':' <idnum> LF 733.... 734 735where `<idnum>` is the number assigned by the frontend to this mark. 736The value of `<idnum>` is expressed as an ASCII decimal integer. 737The value 0 is reserved and cannot be used as 738a mark. Only values greater than or equal to 1 may be used as marks. 739 740New marks are created automatically. Existing marks can be moved 741to another object simply by reusing the same `<idnum>` in another 742`mark` command. 743 744`tag` 745~~~~~ 746Creates an annotated tag referring to a specific commit. To create 747lightweight (non-annotated) tags see the `reset` command below. 748 749.... 750 'tag' SP <name> LF 751 'from' SP <commit-ish> LF 752 'tagger' (SP <name>)? SP LT <email> GT SP <when> LF 753 data 754.... 755 756where `<name>` is the name of the tag to create. 757 758Tag names are automatically prefixed with `refs/tags/` when stored 759in Git, so importing the CVS branch symbol `RELENG-1_0-FINAL` would 760use just `RELENG-1_0-FINAL` for `<name>`, and fast-import will write the 761corresponding ref as `refs/tags/RELENG-1_0-FINAL`. 762 763The value of `<name>` must be a valid refname in Git and therefore 764may contain forward slashes. As `LF` is not valid in a Git refname, 765no quoting or escaping syntax is supported here. 766 767The `from` command is the same as in the `commit` command; see 768above for details. 769 770The `tagger` command uses the same format as `committer` within 771`commit`; again see above for details. 772 773The `data` command following `tagger` must supply the annotated tag 774message (see below for `data` command syntax). To import an empty 775tag message use a 0 length data. Tag messages are free-form and are 776not interpreted by Git. Currently they must be encoded in UTF-8, 777as fast-import does not permit other encodings to be specified. 778 779Signing annotated tags during import from within fast-import is not 780supported. Trying to include your own PGP/GPG signature is not 781recommended, as the frontend does not (easily) have access to the 782complete set of bytes which normally goes into such a signature. 783If signing is required, create lightweight tags from within fast-import with 784`reset`, then create the annotated versions of those tags offline 785with the standard 'git tag' process. 786 787`reset` 788~~~~~~~ 789Creates (or recreates) the named branch, optionally starting from 790a specific revision. The reset command allows a frontend to issue 791a new `from` command for an existing branch, or to create a new 792branch from an existing commit without creating a new commit. 793 794.... 795 'reset' SP <ref> LF 796 ('from' SP <commit-ish> LF)? 797 LF? 798.... 799 800For a detailed description of `<ref>` and `<commit-ish>` see above 801under `commit` and `from`. 802 803The `LF` after the command is optional (it used to be required). 804 805The `reset` command can also be used to create lightweight 806(non-annotated) tags. For example: 807 808==== 809 reset refs/tags/938 810 from :938 811==== 812 813would create the lightweight tag `refs/tags/938` referring to 814whatever commit mark `:938` references. 815 816`blob` 817~~~~~~ 818Requests writing one file revision to the packfile. The revision 819is not connected to any commit; this connection must be formed in 820a subsequent `commit` command by referencing the blob through an 821assigned mark. 822 823.... 824 'blob' LF 825 mark? 826 data 827.... 828 829The mark command is optional here as some frontends have chosen 830to generate the Git SHA-1 for the blob on their own, and feed that 831directly to `commit`. This is typically more work than it's worth 832however, as marks are inexpensive to store and easy to use. 833 834`data` 835~~~~~~ 836Supplies raw data (for use as blob/file content, commit messages, or 837annotated tag messages) to fast-import. Data can be supplied using an exact 838byte count or delimited with a terminating line. Real frontends 839intended for production-quality conversions should always use the 840exact byte count format, as it is more robust and performs better. 841The delimited format is intended primarily for testing fast-import. 842 843Comment lines appearing within the `<raw>` part of `data` commands 844are always taken to be part of the body of the data and are therefore 845never ignored by fast-import. This makes it safe to import any 846file/message content whose lines might start with `#`. 847 848Exact byte count format:: 849 The frontend must specify the number of bytes of data. 850+ 851.... 852 'data' SP <count> LF 853 <raw> LF? 854.... 855+ 856where `<count>` is the exact number of bytes appearing within 857`<raw>`. The value of `<count>` is expressed as an ASCII decimal 858integer. The `LF` on either side of `<raw>` is not 859included in `<count>` and will not be included in the imported data. 860+ 861The `LF` after `<raw>` is optional (it used to be required) but 862recommended. Always including it makes debugging a fast-import 863stream easier as the next command always starts in column 0 864of the next line, even if `<raw>` did not end with an `LF`. 865 866Delimited format:: 867 A delimiter string is used to mark the end of the data. 868 fast-import will compute the length by searching for the delimiter. 869 This format is primarily useful for testing and is not 870 recommended for real data. 871+ 872.... 873 'data' SP '<<' <delim> LF 874 <raw> LF 875 <delim> LF 876 LF? 877.... 878+ 879where `<delim>` is the chosen delimiter string. The string `<delim>` 880must not appear on a line by itself within `<raw>`, as otherwise 881fast-import will think the data ends earlier than it really does. The `LF` 882immediately trailing `<raw>` is part of `<raw>`. This is one of 883the limitations of the delimited format, it is impossible to supply 884a data chunk which does not have an LF as its last byte. 885+ 886The `LF` after `<delim> LF` is optional (it used to be required). 887 888`checkpoint` 889~~~~~~~~~~~~ 890Forces fast-import to close the current packfile, start a new one, and to 891save out all current branch refs, tags and marks. 892 893.... 894 'checkpoint' LF 895 LF? 896.... 897 898Note that fast-import automatically switches packfiles when the current 899packfile reaches --max-pack-size, or 4 GiB, whichever limit is 900smaller. During an automatic packfile switch fast-import does not update 901the branch refs, tags or marks. 902 903As a `checkpoint` can require a significant amount of CPU time and 904disk IO (to compute the overall pack SHA-1 checksum, generate the 905corresponding index file, and update the refs) it can easily take 906several minutes for a single `checkpoint` command to complete. 907 908Frontends may choose to issue checkpoints during extremely large 909and long running imports, or when they need to allow another Git 910process access to a branch. However given that a 30 GiB Subversion 911repository can be loaded into Git through fast-import in about 3 hours, 912explicit checkpointing may not be necessary. 913 914The `LF` after the command is optional (it used to be required). 915 916`progress` 917~~~~~~~~~~ 918Causes fast-import to print the entire `progress` line unmodified to 919its standard output channel (file descriptor 1) when the command is 920processed from the input stream. The command otherwise has no impact 921on the current import, or on any of fast-import's internal state. 922 923.... 924 'progress' SP <any> LF 925 LF? 926.... 927 928The `<any>` part of the command may contain any sequence of bytes 929that does not contain `LF`. The `LF` after the command is optional. 930Callers may wish to process the output through a tool such as sed to 931remove the leading part of the line, for example: 932 933==== 934 frontend | git fast-import | sed 's/^progress //' 935==== 936 937Placing a `progress` command immediately after a `checkpoint` will 938inform the reader when the `checkpoint` has been completed and it 939can safely access the refs that fast-import updated. 940 941`get-mark` 942~~~~~~~~~~ 943Causes fast-import to print the SHA-1 corresponding to a mark to 944stdout or to the file descriptor previously arranged with the 945`--cat-blob-fd` argument. The command otherwise has no impact on the 946current import; its purpose is to retrieve SHA-1s that later commits 947might want to refer to in their commit messages. 948 949.... 950 'get-mark' SP ':' <idnum> LF 951.... 952 953This command can be used anywhere in the stream that comments are 954accepted. In particular, the `get-mark` command can be used in the 955middle of a commit but not in the middle of a `data` command. 956 957See ``Responses To Commands'' below for details about how to read 958this output safely. 959 960`cat-blob` 961~~~~~~~~~~ 962Causes fast-import to print a blob to a file descriptor previously 963arranged with the `--cat-blob-fd` argument. The command otherwise 964has no impact on the current import; its main purpose is to 965retrieve blobs that may be in fast-import's memory but not 966accessible from the target repository. 967 968.... 969 'cat-blob' SP <dataref> LF 970.... 971 972The `<dataref>` can be either a mark reference (`:<idnum>`) 973set previously or a full 40-byte SHA-1 of a Git blob, preexisting or 974ready to be written. 975 976Output uses the same format as `git cat-file --batch`: 977 978==== 979 <sha1> SP 'blob' SP <size> LF 980 <contents> LF 981==== 982 983This command can be used anywhere in the stream that comments are 984accepted. In particular, the `cat-blob` command can be used in the 985middle of a commit but not in the middle of a `data` command. 986 987See ``Responses To Commands'' below for details about how to read 988this output safely. 989 990`ls` 991~~~~ 992Prints information about the object at a path to a file descriptor 993previously arranged with the `--cat-blob-fd` argument. This allows 994printing a blob from the active commit (with `cat-blob`) or copying a 995blob or tree from a previous commit for use in the current one (with 996`filemodify`). 997 998The `ls` command can be used anywhere in the stream that comments are 999accepted, including the middle of a commit.10001001Reading from the active commit::1002 This form can only be used in the middle of a `commit`.1003 The path names a directory entry within fast-import's1004 active commit. The path must be quoted in this case.1005+1006....1007 'ls' SP <path> LF1008....10091010Reading from a named tree::1011 The `<dataref>` can be a mark reference (`:<idnum>`) or the1012 full 40-byte SHA-1 of a Git tag, commit, or tree object,1013 preexisting or waiting to be written.1014 The path is relative to the top level of the tree1015 named by `<dataref>`.1016+1017....1018 'ls' SP <dataref> SP <path> LF1019....10201021See `filemodify` above for a detailed description of `<path>`.10221023Output uses the same format as `git ls-tree <tree> -- <path>`:10241025====1026 <mode> SP ('blob' | 'tree' | 'commit') SP <dataref> HT <path> LF1027====10281029The <dataref> represents the blob, tree, or commit object at <path>1030and can be used in later 'get-mark', 'cat-blob', 'filemodify', or1031'ls' commands.10321033If there is no file or subtree at that path, 'git fast-import' will1034instead report10351036====1037 missing SP <path> LF1038====10391040See ``Responses To Commands'' below for details about how to read1041this output safely.10421043`feature`1044~~~~~~~~~1045Require that fast-import supports the specified feature, or abort if1046it does not.10471048....1049 'feature' SP <feature> ('=' <argument>)? LF1050....10511052The <feature> part of the command may be any one of the following:10531054date-format::1055export-marks::1056relative-marks::1057no-relative-marks::1058force::1059 Act as though the corresponding command-line option with1060 a leading `--` was passed on the command line1061 (see OPTIONS, above).10621063import-marks::1064import-marks-if-exists::1065 Like --import-marks except in two respects: first, only one1066 "feature import-marks" or "feature import-marks-if-exists"1067 command is allowed per stream; second, an --import-marks=1068 or --import-marks-if-exists command-line option overrides1069 any of these "feature" commands in the stream; third,1070 "feature import-marks-if-exists" like a corresponding1071 command-line option silently skips a nonexistent file.10721073get-mark::1074cat-blob::1075ls::1076 Require that the backend support the 'get-mark', 'cat-blob',1077 or 'ls' command respectively.1078 Versions of fast-import not supporting the specified command1079 will exit with a message indicating so.1080 This lets the import error out early with a clear message,1081 rather than wasting time on the early part of an import1082 before the unsupported command is detected.10831084notes::1085 Require that the backend support the 'notemodify' (N)1086 subcommand to the 'commit' command.1087 Versions of fast-import not supporting notes will exit1088 with a message indicating so.10891090done::1091 Error out if the stream ends without a 'done' command.1092 Without this feature, errors causing the frontend to end1093 abruptly at a convenient point in the stream can go1094 undetected. This may occur, for example, if an import1095 front end dies in mid-operation without emitting SIGTERM1096 or SIGKILL at its subordinate git fast-import instance.10971098`option`1099~~~~~~~~1100Processes the specified option so that git fast-import behaves in a1101way that suits the frontend's needs.1102Note that options specified by the frontend are overridden by any1103options the user may specify to git fast-import itself.11041105....1106 'option' SP <option> LF1107....11081109The `<option>` part of the command may contain any of the options1110listed in the OPTIONS section that do not change import semantics,1111without the leading `--` and is treated in the same way.11121113Option commands must be the first commands on the input (not counting1114feature commands), to give an option command after any non-option1115command is an error.11161117The following command-line options change import semantics and may therefore1118not be passed as option:11191120* date-format1121* import-marks1122* export-marks1123* cat-blob-fd1124* force11251126`done`1127~~~~~~1128If the `done` feature is not in use, treated as if EOF was read.1129This can be used to tell fast-import to finish early.11301131If the `--done` command-line option or `feature done` command is1132in use, the `done` command is mandatory and marks the end of the1133stream.11341135RESPONSES TO COMMANDS1136---------------------1137New objects written by fast-import are not available immediately.1138Most fast-import commands have no visible effect until the next1139checkpoint (or completion). The frontend can send commands to1140fill fast-import's input pipe without worrying about how quickly1141they will take effect, which improves performance by simplifying1142scheduling.11431144For some frontends, though, it is useful to be able to read back1145data from the current repository as it is being updated (for1146example when the source material describes objects in terms of1147patches to be applied to previously imported objects). This can1148be accomplished by connecting the frontend and fast-import via1149bidirectional pipes:11501151====1152 mkfifo fast-import-output1153 frontend <fast-import-output |1154 git fast-import >fast-import-output1155====11561157A frontend set up this way can use `progress`, `get-mark`, `ls`, and1158`cat-blob` commands to read information from the import in progress.11591160To avoid deadlock, such frontends must completely consume any1161pending output from `progress`, `ls`, `get-mark`, and `cat-blob` before1162performing writes to fast-import that might block.11631164CRASH REPORTS1165-------------1166If fast-import is supplied invalid input it will terminate with a1167non-zero exit status and create a crash report in the top level of1168the Git repository it was importing into. Crash reports contain1169a snapshot of the internal fast-import state as well as the most1170recent commands that lead up to the crash.11711172All recent commands (including stream comments, file changes and1173progress commands) are shown in the command history within the crash1174report, but raw file data and commit messages are excluded from the1175crash report. This exclusion saves space within the report file1176and reduces the amount of buffering that fast-import must perform1177during execution.11781179After writing a crash report fast-import will close the current1180packfile and export the marks table. This allows the frontend1181developer to inspect the repository state and resume the import from1182the point where it crashed. The modified branches and tags are not1183updated during a crash, as the import did not complete successfully.1184Branch and tag information can be found in the crash report and1185must be applied manually if the update is needed.11861187An example crash:11881189====1190 $ cat >in <<END_OF_INPUT1191 # my very first test commit1192 commit refs/heads/master1193 committer Shawn O. Pearce <spearce> 19283 -04001194 # who is that guy anyway?1195 data <<EOF1196 this is my commit1197 EOF1198 M 644 inline .gitignore1199 data <<EOF1200 .gitignore1201 EOF1202 M 777 inline bob1203 END_OF_INPUT12041205 $ git fast-import <in1206 fatal: Corrupt mode: M 777 inline bob1207 fast-import: dumping crash report to .git/fast_import_crash_843412081209 $ cat .git/fast_import_crash_84341210 fast-import crash report:1211 fast-import process: 84341212 parent process : 13911213 at Sat Sep 1 00:58:12 200712141215 fatal: Corrupt mode: M 777 inline bob12161217 Most Recent Commands Before Crash1218 ---------------------------------1219 # my very first test commit1220 commit refs/heads/master1221 committer Shawn O. Pearce <spearce> 19283 -04001222 # who is that guy anyway?1223 data <<EOF1224 M 644 inline .gitignore1225 data <<EOF1226 * M 777 inline bob12271228 Active Branch LRU1229 -----------------1230 active_branches = 1 cur, 5 max12311232 pos clock name1233 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~1234 1) 0 refs/heads/master12351236 Inactive Branches1237 -----------------1238 refs/heads/master:1239 status : active loaded dirty1240 tip commit : 00000000000000000000000000000000000000001241 old tree : 00000000000000000000000000000000000000001242 cur tree : 00000000000000000000000000000000000000001243 commit clock: 01244 last pack :124512461247 -------------------1248 END OF CRASH REPORT1249====12501251TIPS AND TRICKS1252---------------1253The following tips and tricks have been collected from various1254users of fast-import, and are offered here as suggestions.12551256Use One Mark Per Commit1257~~~~~~~~~~~~~~~~~~~~~~~1258When doing a repository conversion, use a unique mark per commit1259(`mark :<n>`) and supply the --export-marks option on the command1260line. fast-import will dump a file which lists every mark and the Git1261object SHA-1 that corresponds to it. If the frontend can tie1262the marks back to the source repository, it is easy to verify the1263accuracy and completeness of the import by comparing each Git1264commit to the corresponding source revision.12651266Coming from a system such as Perforce or Subversion this should be1267quite simple, as the fast-import mark can also be the Perforce changeset1268number or the Subversion revision number.12691270Freely Skip Around Branches1271~~~~~~~~~~~~~~~~~~~~~~~~~~~1272Don't bother trying to optimize the frontend to stick to one branch1273at a time during an import. Although doing so might be slightly1274faster for fast-import, it tends to increase the complexity of the frontend1275code considerably.12761277The branch LRU builtin to fast-import tends to behave very well, and the1278cost of activating an inactive branch is so low that bouncing around1279between branches has virtually no impact on import performance.12801281Handling Renames1282~~~~~~~~~~~~~~~~1283When importing a renamed file or directory, simply delete the old1284name(s) and modify the new name(s) during the corresponding commit.1285Git performs rename detection after-the-fact, rather than explicitly1286during a commit.12871288Use Tag Fixup Branches1289~~~~~~~~~~~~~~~~~~~~~~1290Some other SCM systems let the user create a tag from multiple1291files which are not from the same commit/changeset. Or to create1292tags which are a subset of the files available in the repository.12931294Importing these tags as-is in Git is impossible without making at1295least one commit which ``fixes up'' the files to match the content1296of the tag. Use fast-import's `reset` command to reset a dummy branch1297outside of your normal branch space to the base commit for the tag,1298then commit one or more file fixup commits, and finally tag the1299dummy branch.13001301For example since all normal branches are stored under `refs/heads/`1302name the tag fixup branch `TAG_FIXUP`. This way it is impossible for1303the fixup branch used by the importer to have namespace conflicts1304with real branches imported from the source (the name `TAG_FIXUP`1305is not `refs/heads/TAG_FIXUP`).13061307When committing fixups, consider using `merge` to connect the1308commit(s) which are supplying file revisions to the fixup branch.1309Doing so will allow tools such as 'git blame' to track1310through the real commit history and properly annotate the source1311files.13121313After fast-import terminates the frontend will need to do `rm .git/TAG_FIXUP`1314to remove the dummy branch.13151316Import Now, Repack Later1317~~~~~~~~~~~~~~~~~~~~~~~~1318As soon as fast-import completes the Git repository is completely valid1319and ready for use. Typically this takes only a very short time,1320even for considerably large projects (100,000+ commits).13211322However repacking the repository is necessary to improve data1323locality and access performance. It can also take hours on extremely1324large projects (especially if -f and a large --window parameter is1325used). Since repacking is safe to run alongside readers and writers,1326run the repack in the background and let it finish when it finishes.1327There is no reason to wait to explore your new Git project!13281329If you choose to wait for the repack, don't try to run benchmarks1330or performance tests until repacking is completed. fast-import outputs1331suboptimal packfiles that are simply never seen in real use1332situations.13331334Repacking Historical Data1335~~~~~~~~~~~~~~~~~~~~~~~~~1336If you are repacking very old imported data (e.g. older than the1337last year), consider expending some extra CPU time and supplying1338--window=50 (or higher) when you run 'git repack'.1339This will take longer, but will also produce a smaller packfile.1340You only need to expend the effort once, and everyone using your1341project will benefit from the smaller repository.13421343Include Some Progress Messages1344~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~1345Every once in a while have your frontend emit a `progress` message1346to fast-import. The contents of the messages are entirely free-form,1347so one suggestion would be to output the current month and year1348each time the current commit date moves into the next month.1349Your users will feel better knowing how much of the data stream1350has been processed.135113521353PACKFILE OPTIMIZATION1354---------------------1355When packing a blob fast-import always attempts to deltify against the last1356blob written. Unless specifically arranged for by the frontend,1357this will probably not be a prior version of the same file, so the1358generated delta will not be the smallest possible. The resulting1359packfile will be compressed, but will not be optimal.13601361Frontends which have efficient access to all revisions of a1362single file (for example reading an RCS/CVS ,v file) can choose1363to supply all revisions of that file as a sequence of consecutive1364`blob` commands. This allows fast-import to deltify the different file1365revisions against each other, saving space in the final packfile.1366Marks can be used to later identify individual file revisions during1367a sequence of `commit` commands.13681369The packfile(s) created by fast-import do not encourage good disk access1370patterns. This is caused by fast-import writing the data in the order1371it is received on standard input, while Git typically organizes1372data within packfiles to make the most recent (current tip) data1373appear before historical data. Git also clusters commits together,1374speeding up revision traversal through better cache locality.13751376For this reason it is strongly recommended that users repack the1377repository with `git repack -a -d` after fast-import completes, allowing1378Git to reorganize the packfiles for faster data access. If blob1379deltas are suboptimal (see above) then also adding the `-f` option1380to force recomputation of all deltas can significantly reduce the1381final packfile size (30-50% smaller can be quite typical).138213831384MEMORY UTILIZATION1385------------------1386There are a number of factors which affect how much memory fast-import1387requires to perform an import. Like critical sections of core1388Git, fast-import uses its own memory allocators to amortize any overheads1389associated with malloc. In practice fast-import tends to amortize any1390malloc overheads to 0, due to its use of large block allocations.13911392per object1393~~~~~~~~~~1394fast-import maintains an in-memory structure for every object written in1395this execution. On a 32 bit system the structure is 32 bytes,1396on a 64 bit system the structure is 40 bytes (due to the larger1397pointer sizes). Objects in the table are not deallocated until1398fast-import terminates. Importing 2 million objects on a 32 bit system1399will require approximately 64 MiB of memory.14001401The object table is actually a hashtable keyed on the object name1402(the unique SHA-1). This storage configuration allows fast-import to reuse1403an existing or already written object and avoid writing duplicates1404to the output packfile. Duplicate blobs are surprisingly common1405in an import, typically due to branch merges in the source.14061407per mark1408~~~~~~~~1409Marks are stored in a sparse array, using 1 pointer (4 bytes or 81410bytes, depending on pointer size) per mark. Although the array1411is sparse, frontends are still strongly encouraged to use marks1412between 1 and n, where n is the total number of marks required for1413this import.14141415per branch1416~~~~~~~~~~1417Branches are classified as active and inactive. The memory usage1418of the two classes is significantly different.14191420Inactive branches are stored in a structure which uses 96 or 1201421bytes (32 bit or 64 bit systems, respectively), plus the length of1422the branch name (typically under 200 bytes), per branch. fast-import will1423easily handle as many as 10,000 inactive branches in under 2 MiB1424of memory.14251426Active branches have the same overhead as inactive branches, but1427also contain copies of every tree that has been recently modified on1428that branch. If subtree `include` has not been modified since the1429branch became active, its contents will not be loaded into memory,1430but if subtree `src` has been modified by a commit since the branch1431became active, then its contents will be loaded in memory.14321433As active branches store metadata about the files contained on that1434branch, their in-memory storage size can grow to a considerable size1435(see below).14361437fast-import automatically moves active branches to inactive status based on1438a simple least-recently-used algorithm. The LRU chain is updated on1439each `commit` command. The maximum number of active branches can be1440increased or decreased on the command line with --active-branches=.14411442per active tree1443~~~~~~~~~~~~~~~1444Trees (aka directories) use just 12 bytes of memory on top of the1445memory required for their entries (see ``per active file'' below).1446The cost of a tree is virtually 0, as its overhead amortizes out1447over the individual file entries.14481449per active file entry1450~~~~~~~~~~~~~~~~~~~~~1451Files (and pointers to subtrees) within active trees require 52 or 641452bytes (32/64 bit platforms) per entry. To conserve space, file and1453tree names are pooled in a common string table, allowing the filename1454``Makefile'' to use just 16 bytes (after including the string header1455overhead) no matter how many times it occurs within the project.14561457The active branch LRU, when coupled with the filename string pool1458and lazy loading of subtrees, allows fast-import to efficiently import1459projects with 2,000+ branches and 45,114+ files in a very limited1460memory footprint (less than 2.7 MiB per active branch).14611462SIGNALS1463-------1464Sending *SIGUSR1* to the 'git fast-import' process ends the current1465packfile early, simulating a `checkpoint` command. The impatient1466operator can use this facility to peek at the objects and refs from an1467import in progress, at the cost of some added running time and worse1468compression.14691470SEE ALSO1471--------1472linkgit:git-fast-export[1]14731474GIT1475---1476Part of the linkgit:git[1] suite