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Merge branch 'master' of git://repo.or.cz/git/fastimport

Browse Source 
* 'master' of git://repo.or.cz/git/fastimport:
  tar archive frontend for fast-import.
  Correct spelling of fast-import in docs.
  Correct some language in fast-import documentation.
  Correct ^0 asciidoc syntax in fast-import docs.
This commit is contained in:
Junio C Hamano
2007-02-08 15:47:08 -08:00
parent cf39f54efc 590dd4bfd2
commit 05b07ab963
2 changed files with 190 additions and 84 deletions
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169
Documentation/git-fast-import.txt
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@ -15,15 +15,15 @@ DESCRIPTION
This program is usually not what the end user wants to run directly. This program is usually not what the end user wants to run directly.
Most end users want to use one of the existing frontend programs, Most end users want to use one of the existing frontend programs,
which parses a specific type of foreign source and feeds the contents which parses a specific type of foreign source and feeds the contents
stored there to git-fast-import (gfi). stored there to git-fast-import.
gfi reads a mixed command/data stream from standard input and fast-import reads a mixed command/data stream from standard input and
writes one or more packfiles directly into the current repository. writes one or more packfiles directly into the current repository.
When EOF is received on standard input, fast import writes out When EOF is received on standard input, fast import writes out
updated branch and tag refs, fully updating the current repository updated branch and tag refs, fully updating the current repository
with the newly imported data. with the newly imported data.
The gfi backend itself can import into an empty repository (one that The fast-import backend itself can import into an empty repository (one that
has already been initialized by gitlink:git-init[1]) or incrementally has already been initialized by gitlink:git-init[1]) or incrementally
update an existing populated repository. Whether or not incremental update an existing populated repository. Whether or not incremental
imports are supported from a particular foreign source depends on imports are supported from a particular foreign source depends on
@ -34,7 +34,7 @@ OPTIONS
------- -------
--date-format=<fmt>:: --date-format=<fmt>::
Specify the type of dates the frontend will supply to Specify the type of dates the frontend will supply to
gfi within `author`, `committer` and `tagger` commands. fast-import within `author`, `committer` and `tagger` commands.
See ``Date Formats'' below for details about which formats See ``Date Formats'' below for details about which formats
are supported, and their syntax. are supported, and their syntax.
@ -65,28 +65,28 @@ OPTIONS
have been completed. have been completed.
--quiet:: --quiet::
Disable all non-fatal output, making gfi silent when it Disable all non-fatal output, making fast-import silent when it
is successful. This option disables the output shown by is successful. This option disables the output shown by
\--stats. \--stats.
--stats:: --stats::
Display some basic statistics about the objects gfi has Display some basic statistics about the objects fast-import has
created, the packfiles they were stored into, and the created, the packfiles they were stored into, and the
memory used by gfi during this run. Showing this output memory used by fast-import during this run. Showing this output
is currently the default, but can be disabled with \--quiet. is currently the default, but can be disabled with \--quiet.
Performance Performance
----------- -----------
The design of gfi allows it to import large projects in a minimum The design of fast-import allows it to import large projects in a minimum
amount of memory usage and processing time. Assuming the frontend amount of memory usage and processing time. Assuming the frontend
is able to keep up with gfi and feed it a constant stream of data, is able to keep up with fast-import and feed it a constant stream of data,
import times for projects holding 10+ years of history and containing import times for projects holding 10+ years of history and containing
100,000+ individual commits are generally completed in just 1-2 100,000+ individual commits are generally completed in just 1-2
hours on quite modest (~$2,000 USD) hardware. hours on quite modest (~$2,000 USD) hardware.
Most bottlenecks appear to be in foreign source data access (the Most bottlenecks appear to be in foreign source data access (the
source just cannot extract revisions fast enough) or disk IO (gfi source just cannot extract revisions fast enough) or disk IO (fast-import
writes as fast as the disk will take the data). Imports will run writes as fast as the disk will take the data). Imports will run
faster if the source data is stored on a different drive than the faster if the source data is stored on a different drive than the
destination Git repository (due to less IO contention). destination Git repository (due to less IO contention).
@ -94,28 +94,28 @@ destination Git repository (due to less IO contention).
Development Cost Development Cost
---------------- ----------------
A typical frontend for gfi tends to weigh in at approximately 200 A typical frontend for fast-import tends to weigh in at approximately 200
lines of Perl/Python/Ruby code. Most developers have been able to lines of Perl/Python/Ruby code. Most developers have been able to
create working importers in just a couple of hours, even though it create working importers in just a couple of hours, even though it
is their first exposure to gfi, and sometimes even to Git. This is is their first exposure to fast-import, and sometimes even to Git. This is
an ideal situation, given that most conversion tools are throw-away an ideal situation, given that most conversion tools are throw-away
(use once, and never look back). (use once, and never look back).
Parallel Operation Parallel Operation
------------------ ------------------
Like `git-push` or `git-fetch`, imports handled by gfi are safe to Like `git-push` or `git-fetch`, imports handled by fast-import are safe to
run alongside parallel `git repack -a -d` or `git gc` invocations, run alongside parallel `git repack -a -d` or `git gc` invocations,
or any other Git operation (including `git prune`, as loose objects or any other Git operation (including `git prune`, as loose objects
are never used by gfi). are never used by fast-import).
gfi does not lock the branch or tag refs it is actively importing. fast-import does not lock the branch or tag refs it is actively importing.
After the import, during its ref update phase, gfi tests each After the import, during its ref update phase, fast-import tests each
existing branch ref to verify the update will be a fast-forward existing branch ref to verify the update will be a fast-forward
update (the commit stored in the ref is contained in the new update (the commit stored in the ref is contained in the new
history of the commit to be written). If the update is not a history of the commit to be written). If the update is not a
fast-forward update, gfi will skip updating that ref and instead fast-forward update, fast-import will skip updating that ref and instead
prints a warning message. gfi will always attempt to update all prints a warning message. fast-import will always attempt to update all
branch refs, and does not stop on the first failure. branch refs, and does not stop on the first failure.
Branch updates can be forced with \--force, but its recommended that Branch updates can be forced with \--force, but its recommended that
@ -125,35 +125,35 @@ is not necessary for an initial import into an empty repository.
Technical Discussion Technical Discussion
-------------------- --------------------
gfi tracks a set of branches in memory. Any branch can be created fast-import tracks a set of branches in memory. Any branch can be created
or modified at any point during the import process by sending a or modified at any point during the import process by sending a
`commit` command on the input stream. This design allows a frontend `commit` command on the input stream. This design allows a frontend
program to process an unlimited number of branches simultaneously, program to process an unlimited number of branches simultaneously,
generating commits in the order they are available from the source generating commits in the order they are available from the source
data. It also simplifies the frontend programs considerably. data. It also simplifies the frontend programs considerably.
gfi does not use or alter the current working directory, or any fast-import does not use or alter the current working directory, or any
file within it. (It does however update the current Git repository, file within it. (It does however update the current Git repository,
as referenced by `GIT_DIR`.) Therefore an import frontend may use as referenced by `GIT_DIR`.) Therefore an import frontend may use
the working directory for its own purposes, such as extracting file the working directory for its own purposes, such as extracting file
revisions from the foreign source. This ignorance of the working revisions from the foreign source. This ignorance of the working
directory also allows gfi to run very quickly, as it does not directory also allows fast-import to run very quickly, as it does not
need to perform any costly file update operations when switching need to perform any costly file update operations when switching
between branches. between branches.
Input Format Input Format
------------ ------------
With the exception of raw file data (which Git does not interpret) With the exception of raw file data (which Git does not interpret)
the gfi input format is text (ASCII) based. This text based the fast-import input format is text (ASCII) based. This text based
format simplifies development and debugging of frontend programs, format simplifies development and debugging of frontend programs,
especially when a higher level language such as Perl, Python or especially when a higher level language such as Perl, Python or
Ruby is being used. Ruby is being used.
gfi is very strict about its input. Where we say SP below we mean fast-import is very strict about its input. Where we say SP below we mean
*exactly* one space. Likewise LF means one (and only one) linefeed. *exactly* one space. Likewise LF means one (and only one) linefeed.
Supplying additional whitespace characters will cause unexpected Supplying additional whitespace characters will cause unexpected
results, such as branch names or file names with leading or trailing results, such as branch names or file names with leading or trailing
spaces in their name, or early termination of gfi when it encounters spaces in their name, or early termination of fast-import when it encounters
unexpected input. unexpected input.
Date Formats Date Formats
@ -164,7 +164,7 @@ in the \--date-format=<fmt> command line option.
`raw`:: `raw`::
This is the Git native format and is `<time> SP <offutc>`. This is the Git native format and is `<time> SP <offutc>`.
It is also gfi's default format, if \--date-format was It is also fast-import's default format, if \--date-format was
not specified. not specified.
+ +
The time of the event is specified by `<time>` as the number of The time of the event is specified by `<time>` as the number of
@ -181,16 +181,16 @@ If the local offset is not available in the source material, use
``+0000'', or the most common local offset. For example many ``+0000'', or the most common local offset. For example many
organizations have a CVS repository which has only ever been accessed organizations have a CVS repository which has only ever been accessed
by users who are located in the same location and timezone. In this by users who are located in the same location and timezone. In this
case the offset from UTC can be easily assumed. case a reasonable offset from UTC could be assumed.
+ +
Unlike the `rfc2822` format, this format is very strict. Any Unlike the `rfc2822` format, this format is very strict. Any
variation in formatting will cause gfi to reject the value. variation in formatting will cause fast-import to reject the value.
`rfc2822`:: `rfc2822`::
This is the standard email format as described by RFC 2822. This is the standard email format as described by RFC 2822.
+ +
An example value is ``Tue Feb 6 11:22:18 2007 -0500''. The Git An example value is ``Tue Feb 6 11:22:18 2007 -0500''. The Git
parser is accurate, but a little on the lenient side. Its the parser is accurate, but a little on the lenient side. It is the
same parser used by gitlink:git-am[1] when applying patches same parser used by gitlink:git-am[1] when applying patches
received from email. received from email.
+ +
@ -205,14 +205,15 @@ contained in an RFC 2822 date string is used to adjust the date
value to UTC prior to storage. Therefore it is important that value to UTC prior to storage. Therefore it is important that
this information be as accurate as possible. this information be as accurate as possible.
+ +
If the source material is formatted in RFC 2822 style dates, If the source material uses RFC 2822 style dates,
the frontend should let gfi handle the parsing and conversion the frontend should let fast-import handle the parsing and conversion
(rather than attempting to do it itself) as the Git parser has (rather than attempting to do it itself) as the Git parser has
been well tested in the wild. been well tested in the wild.
+ +
Frontends should prefer the `raw` format if the source material Frontends should prefer the `raw` format if the source material
is already in UNIX-epoch format, or is easily convertible to already uses UNIX-epoch format, can be coaxed to give dates in that
that format, as there is no ambiguity in parsing. format, or its format is easiliy convertible to it, as there is no
ambiguity in parsing.
`now`:: `now`::
Always use the current time and timezone. The literal Always use the current time and timezone. The literal
@ -220,7 +221,7 @@ that format, as there is no ambiguity in parsing.
+ +
This is a toy format. The current time and timezone of this system This is a toy format. The current time and timezone of this system
is always copied into the identity string at the time it is being is always copied into the identity string at the time it is being
created by gfi. There is no way to specify a different time or created by fast-import. There is no way to specify a different time or
timezone. timezone.
+ +
This particular format is supplied as its short to implement and This particular format is supplied as its short to implement and
@ -237,7 +238,7 @@ date format other than `now`.
Commands Commands
~~~~~~~~ ~~~~~~~~
gfi accepts several commands to update the current repository fast-import accepts several commands to update the current repository
and control the current import process. More detailed discussion and control the current import process. More detailed discussion
(with examples) of each command follows later. (with examples) of each command follows later.
@ -263,7 +264,7 @@ and control the current import process. More detailed discussion
needed to perform an import. needed to perform an import.
`checkpoint`:: `checkpoint`::
Forces gfi to close the current packfile, generate its Forces fast-import to close the current packfile, generate its
unique SHA-1 checksum and index, and start a new packfile. unique SHA-1 checksum and index, and start a new packfile.
This command is optional and is not needed to perform This command is optional and is not needed to perform
an import. an import.
@ -292,7 +293,7 @@ Git, so importing the CVS branch symbol `RELENG-1_0` would use
`<ref>` must be a valid refname in Git. As `LF` is not valid in `<ref>` must be a valid refname in Git. As `LF` is not valid in
a Git refname, no quoting or escaping syntax is supported here. a Git refname, no quoting or escaping syntax is supported here.
A `mark` command may optionally appear, requesting gfi to save a A `mark` command may optionally appear, requesting fast-import to save a
reference to the newly created commit for future use by the frontend reference to the newly created commit for future use by the frontend
(see below for format). It is very common for frontends to mark (see below for format). It is very common for frontends to mark
every commit they create, thereby allowing future branch creation every commit they create, thereby allowing future branch creation
@ -302,7 +303,7 @@ The `data` command following `committer` must supply the commit
message (see below for `data` command syntax). To import an empty message (see below for `data` command syntax). To import an empty
commit message use a 0 length data. Commit messages are free-form commit message use a 0 length data. Commit messages are free-form
and are not interpreted by Git. Currently they must be encoded in and are not interpreted by Git. Currently they must be encoded in
UTF-8, as gfi does not permit other encodings to be specified. UTF-8, as fast-import does not permit other encodings to be specified.
Zero or more `filemodify`, `filedelete` and `filedeleteall` commands Zero or more `filemodify`, `filedelete` and `filedeleteall` commands
may be included to update the contents of the branch prior to may be included to update the contents of the branch prior to
@ -315,7 +316,7 @@ wipes the branch clean (see below).
^^^^^^^^ ^^^^^^^^
An `author` command may optionally appear, if the author information An `author` command may optionally appear, if the author information
might differ from the committer information. If `author` is omitted might differ from the committer information. If `author` is omitted
then gfi will automatically use the committer's information for then fast-import will automatically use the committer's information for
the author portion of the commit. See below for a description of the author portion of the commit. See below for a description of
the fields in `author`, as they are identical to `committer`. the fields in `author`, as they are identical to `committer`.
@ -340,12 +341,12 @@ their syntax.
`from` `from`
^^^^^^ ^^^^^^
Only valid for the first commit made on this branch by this Only valid for the first commit made on this branch by this
gfi process. The `from` command is used to specify the commit fast-import process. The `from` command is used to specify the commit
to initialize this branch from. This revision will be the first to initialize this branch from. This revision will be the first
ancestor of the new commit. ancestor of the new commit.
Omitting the `from` command in the first commit of a new branch will Omitting the `from` command in the first commit of a new branch will
cause gfi to create that commit with no ancestor. This tends to be cause fast-import to create that commit with no ancestor. This tends to be
desired only for the initial commit of a project. Omitting the desired only for the initial commit of a project. Omitting the
`from` command on existing branches is required, as the current `from` command on existing branches is required, as the current
commit on that branch is automatically assumed to be the first commit on that branch is automatically assumed to be the first
@ -356,13 +357,13 @@ quoting or escaping syntax is supported within `<committish>`.
Here `<committish>` is any of the following: Here `<committish>` is any of the following:
* The name of an existing branch already in gfi's internal branch * The name of an existing branch already in fast-import's internal branch
table. If gfi doesn't know the name, its treated as a SHA-1 table. If fast-import doesn't know the name, its treated as a SHA-1
expression. expression.
* A mark reference, `:<idnum>`, where `<idnum>` is the mark number. * A mark reference, `:<idnum>`, where `<idnum>` is the mark number.
+ +
The reason gfi uses `:` to denote a mark reference is this character The reason fast-import uses `:` to denote a mark reference is this character
is not legal in a Git branch name. The leading `:` makes it easy is not legal in a Git branch name. The leading `:` makes it easy
to distingush between the mark 42 (`:42`) and the branch 42 (`42` to distingush between the mark 42 (`:42`) and the branch 42 (`42`
or `refs/heads/42`), or an abbreviated SHA-1 which happened to or `refs/heads/42`), or an abbreviated SHA-1 which happened to
@ -380,10 +381,10 @@ current branch value should be written as:
---- ----
from refs/heads/branch^0 from refs/heads/branch^0
---- ----
The `^0` suffix is necessary as gfi does not permit a branch to The `{caret}0` suffix is necessary as fast-import does not permit a branch to
start from itself, and the branch is created in memory before the start from itself, and the branch is created in memory before the
`from` command is even read from the input. Adding `^0` will force `from` command is even read from the input. Adding `{caret}0` will force
gfi to resolve the commit through Git's revision parsing library, fast-import to resolve the commit through Git's revision parsing library,
rather than its internal branch table, thereby loading in the rather than its internal branch table, thereby loading in the
existing value of the branch. existing value of the branch.
@ -391,7 +392,7 @@ existing value of the branch.
^^^^^^^ ^^^^^^^
Includes one additional ancestor commit, and makes the current Includes one additional ancestor commit, and makes the current
commit a merge commit. An unlimited number of `merge` commands per commit a merge commit. An unlimited number of `merge` commands per
commit are permitted by gfi, thereby establishing an n-way merge. commit are permitted by fast-import, thereby establishing an n-way merge.
However Git's other tools never create commits with more than 15 However Git's other tools never create commits with more than 15
additional ancestors (forming a 16-way merge). For this reason additional ancestors (forming a 16-way merge). For this reason
it is suggested that frontends do not use more than 15 `merge` it is suggested that frontends do not use more than 15 `merge`
@ -492,14 +493,14 @@ update the content.
Issuing a `filedeleteall` followed by the needed `filemodify` Issuing a `filedeleteall` followed by the needed `filemodify`
commands to set the correct content will produce the same results commands to set the correct content will produce the same results
as sending only the needed `filemodify` and `filedelete` commands. as sending only the needed `filemodify` and `filedelete` commands.
The `filedeleteall` approach may however require gfi to use slightly The `filedeleteall` approach may however require fast-import to use slightly
more memory per active branch (less than 1 MiB for even most large more memory per active branch (less than 1 MiB for even most large
projects); so frontends that can easily obtain only the affected projects); so frontends that can easily obtain only the affected
paths for a commit are encouraged to do so. paths for a commit are encouraged to do so.
`mark` `mark`
~~~~~~ ~~~~~~
Arranges for gfi to save a reference to the current object, allowing Arranges for fast-import to save a reference to the current object, allowing
the frontend to recall this object at a future point in time, without the frontend to recall this object at a future point in time, without
knowing its SHA-1. Here the current object is the object creation knowing its SHA-1. Here the current object is the object creation
command the `mark` command appears within. This can be `commit`, command the `mark` command appears within. This can be `commit`,
@ -535,7 +536,7 @@ where `<name>` is the name of the tag to create.
Tag names are automatically prefixed with `refs/tags/` when stored Tag names are automatically prefixed with `refs/tags/` when stored
in Git, so importing the CVS branch symbol `RELENG-1_0-FINAL` would in Git, so importing the CVS branch symbol `RELENG-1_0-FINAL` would
use just `RELENG-1_0-FINAL` for `<name>`, and gfi will write the use just `RELENG-1_0-FINAL` for `<name>`, and fast-import will write the
corresponding ref as `refs/tags/RELENG-1_0-FINAL`. corresponding ref as `refs/tags/RELENG-1_0-FINAL`.
The value of `<name>` must be a valid refname in Git and therefore The value of `<name>` must be a valid refname in Git and therefore
@ -552,13 +553,13 @@ The `data` command following `tagger` must supply the annotated tag
message (see below for `data` command syntax). To import an empty message (see below for `data` command syntax). To import an empty
tag message use a 0 length data. Tag messages are free-form and are tag message use a 0 length data. Tag messages are free-form and are
not interpreted by Git. Currently they must be encoded in UTF-8, not interpreted by Git. Currently they must be encoded in UTF-8,
as gfi does not permit other encodings to be specified. as fast-import does not permit other encodings to be specified.
Signing annotated tags during import from within gfi is not Signing annotated tags during import from within fast-import is not
supported. Trying to include your own PGP/GPG signature is not supported. Trying to include your own PGP/GPG signature is not
recommended, as the frontend does not (easily) have access to the recommended, as the frontend does not (easily) have access to the
complete set of bytes which normally goes into such a signature. complete set of bytes which normally goes into such a signature.
If signing is required, create lightweight tags from within gfi with If signing is required, create lightweight tags from within fast-import with
`reset`, then create the annotated versions of those tags offline `reset`, then create the annotated versions of those tags offline
with the standard gitlink:git-tag[1] process. with the standard gitlink:git-tag[1] process.
@ -610,11 +611,11 @@ however, as marks are inexpensive to store and easy to use.
`data` `data`
~~~~~~ ~~~~~~
Supplies raw data (for use as blob/file content, commit messages, or Supplies raw data (for use as blob/file content, commit messages, or
annotated tag messages) to gfi. Data can be supplied using an exact annotated tag messages) to fast-import. Data can be supplied using an exact
byte count or delimited with a terminating line. Real frontends byte count or delimited with a terminating line. Real frontends
intended for production-quality conversions should always use the intended for production-quality conversions should always use the
exact byte count format, as it is more robust and performs better. exact byte count format, as it is more robust and performs better.
The delimited format is intended primarily for testing gfi. The delimited format is intended primarily for testing fast-import.
Exact byte count format:: Exact byte count format::
The frontend must specify the number of bytes of data. The frontend must specify the number of bytes of data.
@ -631,7 +632,7 @@ included in `<count>` and will not be included in the imported data.
Delimited format:: Delimited format::
A delimiter string is used to mark the end of the data. A delimiter string is used to mark the end of the data.
gfi will compute the length by searching for the delimiter. fast-import will compute the length by searching for the delimiter.
This format is primarly useful for testing and is not This format is primarly useful for testing and is not
recommended for real data. recommended for real data.
+ +
@ -643,14 +644,14 @@ Delimited format::
+ +
where `<delim>` is the chosen delimiter string. The string `<delim>` where `<delim>` is the chosen delimiter string. The string `<delim>`
must not appear on a line by itself within `<raw>`, as otherwise must not appear on a line by itself within `<raw>`, as otherwise
gfi will think the data ends earlier than it really does. The `LF` fast-import will think the data ends earlier than it really does. The `LF`
immediately trailing `<raw>` is part of `<raw>`. This is one of immediately trailing `<raw>` is part of `<raw>`. This is one of
the limitations of the delimited format, it is impossible to supply the limitations of the delimited format, it is impossible to supply
a data chunk which does not have an LF as its last byte. a data chunk which does not have an LF as its last byte.
`checkpoint` `checkpoint`
~~~~~~~~~~~~ ~~~~~~~~~~~~
Forces gfi to close the current packfile, start a new one, and to Forces fast-import to close the current packfile, start a new one, and to
save out all current branch refs, tags and marks. save out all current branch refs, tags and marks.
.... ....
@ -658,9 +659,9 @@ save out all current branch refs, tags and marks.
LF LF
.... ....
Note that gfi automatically switches packfiles when the current Note that fast-import automatically switches packfiles when the current
packfile reaches \--max-pack-size, or 4 GiB, whichever limit is packfile reaches \--max-pack-size, or 4 GiB, whichever limit is
smaller. During an automatic packfile switch gfi does not update smaller. During an automatic packfile switch fast-import does not update
the branch refs, tags or marks. the branch refs, tags or marks.
As a `checkpoint` can require a significant amount of CPU time and As a `checkpoint` can require a significant amount of CPU time and
@ -671,37 +672,37 @@ several minutes for a single `checkpoint` command to complete.
Frontends may choose to issue checkpoints during extremely large Frontends may choose to issue checkpoints during extremely large
and long running imports, or when they need to allow another Git and long running imports, or when they need to allow another Git
process access to a branch. However given that a 30 GiB Subversion process access to a branch. However given that a 30 GiB Subversion
repository can be loaded into Git through gfi in about 3 hours, repository can be loaded into Git through fast-import in about 3 hours,
explicit checkpointing may not be necessary. explicit checkpointing may not be necessary.
Tips and Tricks Tips and Tricks
--------------- ---------------
The following tips and tricks have been collected from various The following tips and tricks have been collected from various
users of gfi, and are offered here as suggestions. users of fast-import, and are offered here as suggestions.
Use One Mark Per Commit Use One Mark Per Commit
~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~
When doing a repository conversion, use a unique mark per commit When doing a repository conversion, use a unique mark per commit
(`mark :<n>`) and supply the \--export-marks option on the command (`mark :<n>`) and supply the \--export-marks option on the command
line. gfi will dump a file which lists every mark and the Git line. fast-import will dump a file which lists every mark and the Git
object SHA-1 that corresponds to it. If the frontend can tie object SHA-1 that corresponds to it. If the frontend can tie
the marks back to the source repository, it is easy to verify the the marks back to the source repository, it is easy to verify the
accuracy and completeness of the import by comparing each Git accuracy and completeness of the import by comparing each Git
commit to the corresponding source revision. commit to the corresponding source revision.
Coming from a system such as Perforce or Subversion this should be Coming from a system such as Perforce or Subversion this should be
quite simple, as the gfi mark can also be the Perforce changeset quite simple, as the fast-import mark can also be the Perforce changeset
number or the Subversion revision number. number or the Subversion revision number.
Freely Skip Around Branches Freely Skip Around Branches
~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~
Don't bother trying to optimize the frontend to stick to one branch Don't bother trying to optimize the frontend to stick to one branch
at a time during an import. Although doing so might be slightly at a time during an import. Although doing so might be slightly
faster for gfi, it tends to increase the complexity of the frontend faster for fast-import, it tends to increase the complexity of the frontend
code considerably. code considerably.
The branch LRU builtin to gfi tends to behave very well, and the The branch LRU builtin to fast-import tends to behave very well, and the
cost of activating an inactive branch is so low that bouncing around cost of activating an inactive branch is so low that bouncing around
between branches has virtually no impact on import performance. between branches has virtually no impact on import performance.
@ -713,7 +714,7 @@ tags which are a subset of the files available in the repository.
Importing these tags as-is in Git is impossible without making at Importing these tags as-is in Git is impossible without making at
least one commit which ``fixes up'' the files to match the content least one commit which ``fixes up'' the files to match the content
of the tag. Use gfi's `reset` command to reset a dummy branch of the tag. Use fast-import's `reset` command to reset a dummy branch
outside of your normal branch space to the base commit for the tag, outside of your normal branch space to the base commit for the tag,
then commit one or more file fixup commits, and finally tag the then commit one or more file fixup commits, and finally tag the
dummy branch. dummy branch.
@ -730,12 +731,12 @@ Doing so will allow tools such as gitlink:git-blame[1] to track
through the real commit history and properly annotate the source through the real commit history and properly annotate the source
files. files.
After gfi terminates the frontend will need to do `rm .git/TAG_FIXUP` After fast-import terminates the frontend will need to do `rm .git/TAG_FIXUP`
to remove the dummy branch. to remove the dummy branch.
Import Now, Repack Later Import Now, Repack Later
~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~
As soon as gfi completes the Git repository is completely valid As soon as fast-import completes the Git repository is completely valid
and ready for use. Typicallly this takes only a very short time, and ready for use. Typicallly this takes only a very short time,
even for considerably large projects (100,000+ commits). even for considerably large projects (100,000+ commits).
@ -747,7 +748,7 @@ run the repack in the background and let it finish when it finishes.
There is no reason to wait to explore your new Git project! There is no reason to wait to explore your new Git project!
If you choose to wait for the repack, don't try to run benchmarks If you choose to wait for the repack, don't try to run benchmarks
or performance tests until repacking is completed. gfi outputs or performance tests until repacking is completed. fast-import outputs
suboptimal packfiles that are simply never seen in real use suboptimal packfiles that are simply never seen in real use
situations. situations.
@ -763,7 +764,7 @@ project will benefit from the smaller repository.
Packfile Optimization Packfile Optimization
--------------------- ---------------------
When packing a blob gfi always attempts to deltify against the last When packing a blob fast-import always attempts to deltify against the last
blob written. Unless specifically arranged for by the frontend, blob written. Unless specifically arranged for by the frontend,
this will probably not be a prior version of the same file, so the this will probably not be a prior version of the same file, so the
generated delta will not be the smallest possible. The resulting generated delta will not be the smallest possible. The resulting
@ -772,20 +773,20 @@ packfile will be compressed, but will not be optimal.
Frontends which have efficient access to all revisions of a Frontends which have efficient access to all revisions of a
single file (for example reading an RCS/CVS ,v file) can choose single file (for example reading an RCS/CVS ,v file) can choose
to supply all revisions of that file as a sequence of consecutive to supply all revisions of that file as a sequence of consecutive
`blob` commands. This allows gfi to deltify the different file `blob` commands. This allows fast-import to deltify the different file
revisions against each other, saving space in the final packfile. revisions against each other, saving space in the final packfile.
Marks can be used to later identify individual file revisions during Marks can be used to later identify individual file revisions during
a sequence of `commit` commands. a sequence of `commit` commands.
The packfile(s) created by gfi do not encourage good disk access The packfile(s) created by fast-import do not encourage good disk access
patterns. This is caused by gfi writing the data in the order patterns. This is caused by fast-import writing the data in the order
it is received on standard input, while Git typically organizes it is received on standard input, while Git typically organizes
data within packfiles to make the most recent (current tip) data data within packfiles to make the most recent (current tip) data
appear before historical data. Git also clusters commits together, appear before historical data. Git also clusters commits together,
speeding up revision traversal through better cache locality. speeding up revision traversal through better cache locality.
For this reason it is strongly recommended that users repack the For this reason it is strongly recommended that users repack the
repository with `git repack -a -d` after gfi completes, allowing repository with `git repack -a -d` after fast-import completes, allowing
Git to reorganize the packfiles for faster data access. If blob Git to reorganize the packfiles for faster data access. If blob
deltas are suboptimal (see above) then also adding the `-f` option deltas are suboptimal (see above) then also adding the `-f` option
to force recomputation of all deltas can significantly reduce the to force recomputation of all deltas can significantly reduce the
@ -794,23 +795,23 @@ final packfile size (30-50% smaller can be quite typical).
Memory Utilization Memory Utilization
------------------ ------------------
There are a number of factors which affect how much memory gfi There are a number of factors which affect how much memory fast-import
requires to perform an import. Like critical sections of core requires to perform an import. Like critical sections of core
Git, gfi uses its own memory allocators to ammortize any overheads Git, fast-import uses its own memory allocators to ammortize any overheads
associated with malloc. In practice gfi tends to ammoritize any associated with malloc. In practice fast-import tends to ammoritize any
malloc overheads to 0, due to its use of large block allocations. malloc overheads to 0, due to its use of large block allocations.
per object per object
~~~~~~~~~~ ~~~~~~~~~~
gfi maintains an in-memory structure for every object written in fast-import maintains an in-memory structure for every object written in
this execution. On a 32 bit system the structure is 32 bytes, this execution. On a 32 bit system the structure is 32 bytes,
on a 64 bit system the structure is 40 bytes (due to the larger on a 64 bit system the structure is 40 bytes (due to the larger
pointer sizes). Objects in the table are not deallocated until pointer sizes). Objects in the table are not deallocated until
gfi terminates. Importing 2 million objects on a 32 bit system fast-import terminates. Importing 2 million objects on a 32 bit system
will require approximately 64 MiB of memory. will require approximately 64 MiB of memory.
The object table is actually a hashtable keyed on the object name The object table is actually a hashtable keyed on the object name
(the unique SHA-1). This storage configuration allows gfi to reuse (the unique SHA-1). This storage configuration allows fast-import to reuse
an existing or already written object and avoid writing duplicates an existing or already written object and avoid writing duplicates
to the output packfile. Duplicate blobs are surprisingly common to the output packfile. Duplicate blobs are surprisingly common
in an import, typically due to branch merges in the source. in an import, typically due to branch merges in the source.
@ -830,7 +831,7 @@ of the two classes is significantly different.
Inactive branches are stored in a structure which uses 96 or 120 Inactive branches are stored in a structure which uses 96 or 120
bytes (32 bit or 64 bit systems, respectively), plus the length of bytes (32 bit or 64 bit systems, respectively), plus the length of
the branch name (typically under 200 bytes), per branch. gfi will the branch name (typically under 200 bytes), per branch. fast-import will
easily handle as many as 10,000 inactive branches in under 2 MiB easily handle as many as 10,000 inactive branches in under 2 MiB
of memory. of memory.
@ -845,7 +846,7 @@ As active branches store metadata about the files contained on that
branch, their in-memory storage size can grow to a considerable size branch, their in-memory storage size can grow to a considerable size
(see below). (see below).
gfi automatically moves active branches to inactive status based on fast-import automatically moves active branches to inactive status based on
a simple least-recently-used algorithm. The LRU chain is updated on a simple least-recently-used algorithm. The LRU chain is updated on
each `commit` command. The maximum number of active branches can be each `commit` command. The maximum number of active branches can be
increased or decreased on the command line with \--active-branches=. increased or decreased on the command line with \--active-branches=.
@ -866,7 +867,7 @@ tree names are pooled in a common string table, allowing the filename
overhead) no matter how many times it occurs within the project. overhead) no matter how many times it occurs within the project.
The active branch LRU, when coupled with the filename string pool The active branch LRU, when coupled with the filename string pool
and lazy loading of subtrees, allows gfi to efficiently import and lazy loading of subtrees, allows fast-import to efficiently import
projects with 2,000+ branches and 45,114+ files in a very limited projects with 2,000+ branches and 45,114+ files in a very limited
memory footprint (less than 2.7 MiB per active branch). memory footprint (less than 2.7 MiB per active branch).

105
contrib/fast-import/import-tars.perl Executable file
View File

@ -0,0 +1,105 @@
#!/usr/bin/perl
## tar archive frontend for git-fast-import
##
## For example:
##
## mkdir project; cd project; git init
## perl import-tars.perl *.tar.bz2
## git whatchanged import-tars
##
use strict;
die "usage: import-tars *.tar.{gz,bz2,Z}\n" unless @ARGV;
my $branch_name = 'import-tars';
my $branch_ref = "refs/heads/$branch_name";
my $committer_name = 'T Ar Creator';
my $committer_email = 'tar@example.com';
open(FI, '|-', 'git', 'fast-import', '--quiet')
or die "Unable to start git fast-import: $!\n";
foreach my $tar_file (@ARGV)
{
$tar_file =~ m,([^/]+)$,;
my $tar_name = $1;
if ($tar_name =~ s/\.(tar\.gz|tgz)$//) {
open(I, '-|', 'gzcat', $tar_file) or die "Unable to gzcat $tar_file: $!\n";
} elsif ($tar_name =~ s/\.(tar\.bz2|tbz2)$//) {
open(I, '-|', 'bzcat', $tar_file) or die "Unable to bzcat $tar_file: $!\n";
} elsif ($tar_name =~ s/\.tar\.Z$//) {
open(I, '-|', 'zcat', $tar_file) or die "Unable to zcat $tar_file: $!\n";
} elsif ($tar_name =~ s/\.tar$//) {
open(I, $tar_file) or die "Unable to open $tar_file: $!\n";
} else {
die "Unrecognized compression format: $tar_file\n";
}
my $commit_time = 0;
my $next_mark = 1;
my $have_top_dir = 1;
my ($top_dir, %files);
while (read(I, $_, 512) == 512) {
my ($name, $mode, $uid, $gid, $size, $mtime,
$chksum, $typeflag, $linkname, $magic,
$version, $uname, $gname, $devmajor, $devminor,
$prefix) = unpack 'Z100 Z8 Z8 Z8 Z12 Z12
Z8 Z1 Z100 Z6
Z2 Z32 Z32 Z8 Z8 Z*', $_;
last unless $name;
$mode = oct $mode;
$size = oct $size;
$mtime = oct $mtime;
next if $mode & 0040000;
print FI "blob\n", "mark :$next_mark\n", "data $size\n";
while ($size > 0 && read(I, $_, 512) == 512) {
print FI substr($_, 0, $size);
$size -= 512;
}
print FI "\n";
my $path = "$prefix$name";
$files{$path} = [$next_mark++, $mode];
$commit_time = $mtime if $mtime > $commit_time;
$path =~ m,^([^/]+)/,;
$top_dir = $1 unless $top_dir;
$have_top_dir = 0 if $top_dir ne $1;
}
print FI <<EOF;
commit $branch_ref
committer $committer_name <$committer_email> $commit_time +0000
data <<END_OF_COMMIT_MESSAGE
Imported from $tar_file.
END_OF_COMMIT_MESSAGE
deleteall
EOF
foreach my $path (keys %files)
{
my ($mark, $mode) = @{$files{$path}};
my $git_mode = 0644;
$git_mode |= 0700 if $mode & 0111;
$path =~ s,^([^/]+)/,, if $have_top_dir;
printf FI "M %o :%i %s\n", $git_mode, $mark, $path;
}
print FI "\n";
print FI <<EOF;
tag $tar_name
from $branch_ref
tagger $committer_name <$committer_email> $commit_time +0000
data <<END_OF_TAG_MESSAGE
Package $tar_name
END_OF_TAG_MESSAGE
EOF
close I;
}
close FI;