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index eaba6fd4c168564f43ce2db3994dcb7b70bd4b54..d5119678b59492db4651006391fd693a1a12601a 100644 (file)
spaces in their name, or early termination of fast-import when it encounters
unexpected input.
+Stream Comments
+~~~~~~~~~~~~~~~
+To aid in debugging frontends fast-import ignores any line that
+begins with `#` (ASCII pound/hash) up to and including the line
+ending `LF`. A comment line may contain any sequence of bytes
+that does not contain an LF and therefore may be used to include
+any detailed debugging information that might be specific to the
+frontend and useful when inspecting a fast-import data stream.
+
Date Formats
~~~~~~~~~~~~
The following date formats are supported. A frontend should select
+
Frontends should prefer the `raw` format if the source material
already uses UNIX-epoch format, can be coaxed to give dates in that
-format, or its format is easiliy convertible to it, as there is no
+format, or its format is easily convertible to it, as there is no
ambiguity in parsing.
`now`::
This command is optional and is not needed to perform
an import.
+`progress`::
+ Causes fast-import to echo the entire line to its own
+ standard output. This command is optional and is not needed
+ to perform an import.
+
`commit`
~~~~~~~~
Create or update a branch with a new commit, recording one logical
data
('from' SP <committish> LF)?
('merge' SP <committish> LF)?
- (filemodify | filedelete | filedeleteall)*
- LF
+ (filemodify | filedelete | filecopy | filerename | filedeleteall)*
+ LF?
....
where `<ref>` is the name of the branch to make the commit on.
and are not interpreted by Git. Currently they must be encoded in
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`, `filecopy`, `filerename`
+and `filedeleteall` commands
may be included to update the contents of the branch prior to
creating the commit. These commands may be supplied in any order.
-However it is recommended that a `filedeleteall` command preceed
-all `filemodify` commands in the same commit, as `filedeleteall`
+However it is recommended that a `filedeleteall` command precede
+all `filemodify`, `filecopy` and `filerename` commands in the same
+commit, as `filedeleteall`
wipes the branch clean (see below).
+The `LF` after the command is optional (it used to be required).
+
`author`
^^^^^^^^
An `author` command may optionally appear, if the author information
+
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
-to distingush between the mark 42 (`:42`) and the branch 42 (`42`
+to distinguish between the mark 42 (`:42`) and the branch 42 (`42`
or `refs/heads/42`), or an abbreviated SHA-1 which happened to
consist only of base-10 digits.
+
If an `LF` or double quote must be encoded into `<path>` shell-style
quoting should be used, e.g. `"path/with\n and \" in it"`.
-The value of `<path>` must be in canoncial form. That is it must not:
+The value of `<path>` must be in canonical form. That is it must not:
* contain an empty directory component (e.g. `foo//bar` is invalid),
* end with a directory separator (e.g. `foo/` is invalid),
`filedelete`
^^^^^^^^^^^^
-Included in a `commit` command to remove a file from the branch.
-If the file removal makes its directory empty, the directory will
+Included in a `commit` command to remove a file or recursively
+delete an entire directory from the branch. If the file or directory
+removal makes its parent directory empty, the parent directory will
be automatically removed too. This cascades up the tree until the
first non-empty directory or the root is reached.
'D' SP <path> LF
....
-here `<path>` is the complete path of the file to be removed.
+here `<path>` is the complete path of the file or subdirectory to
+be removed from the branch.
See `filemodify` above for a detailed description of `<path>`.
+`filecopy`
+^^^^^^^^^^^^
+Recursively copies an existing file or subdirectory to a different
+location within the branch. The existing file or directory must
+exist. If the destination exists it will be completely replaced
+by the content copied from the source.
+
+....
+ 'C' SP <path> SP <path> LF
+....
+
+here the first `<path>` is the source location and the second
+`<path>` is the destination. See `filemodify` above for a detailed
+description of what `<path>` may look like. To use a source path
+that contains SP the path must be quoted.
+
+A `filecopy` command takes effect immediately. Once the source
+location has been copied to the destination any future commands
+applied to the source location will not impact the destination of
+the copy.
+
+`filerename`
+^^^^^^^^^^^^
+Renames an existing file or subdirectory to a different location
+within the branch. The existing file or directory must exist. If
+the destination exists it will be replaced by the source directory.
+
+....
+ 'R' SP <path> SP <path> LF
+....
+
+here the first `<path>` is the source location and the second
+`<path>` is the destination. See `filemodify` above for a detailed
+description of what `<path>` may look like. To use a source path
+that contains SP the path must be quoted.
+
+A `filerename` command takes effect immediately. Once the source
+location has been renamed to the destination any future commands
+applied to the source location will create new files there and not
+impact the destination of the rename.
+
+Note that a `filerename` is the same as a `filecopy` followed by a
+`filedelete` of the source location. There is a slight performance
+advantage to using `filerename`, but the advantage is so small
+that it is never worth trying to convert a delete/add pair in
+source material into a rename for fast-import. This `filerename`
+command is provided just to simplify frontends that already have
+rename information and don't want bother with decomposing it into a
+`filecopy` followed by a `filedelete`.
+
`filedeleteall`
^^^^^^^^^^^^^^^
Included in a `commit` command to remove all files (and also all
'from' SP <committish> LF
'tagger' SP <name> SP LT <email> GT SP <when> LF
data
- LF
....
where `<name>` is the name of the tag to create.
....
'reset' SP <ref> LF
('from' SP <committish> LF)?
- LF
+ LF?
....
For a detailed description of `<ref>` and `<committish>` see above
under `commit` and `from`.
+The `LF` after the command is optional (it used to be required).
+
The `reset` command can also be used to create lightweight
(non-annotated) tags. For example:
exact byte count format, as it is more robust and performs better.
The delimited format is intended primarily for testing fast-import.
+Comment lines appearing within the `<raw>` part of `data` commands
+are always taken to be part of the body of the data and are therefore
+never ignored by fast-import. This makes it safe to import any
+file/message content whose lines might start with `#`.
+
Exact byte count format::
The frontend must specify the number of bytes of data.
+
....
'data' SP <count> LF
- <raw> LF
+ <raw> LF?
....
+
where `<count>` is the exact number of bytes appearing within
`<raw>`. The value of `<count>` is expressed as an ASCII decimal
integer. The `LF` on either side of `<raw>` is not
included in `<count>` and will not be included in the imported data.
++
+The `LF` after `<raw>` is optional (it used to be required) but
+recommended. Always including it makes debugging a fast-import
+stream easier as the next command always starts in column 0
+of the next line, even if `<raw>` did not end with an `LF`.
Delimited format::
A delimiter string is used to mark the end of the data.
fast-import will compute the length by searching for the delimiter.
- This format is primarly useful for testing and is not
+ This format is primarily useful for testing and is not
recommended for real data.
+
....
'data' SP '<<' <delim> LF
<raw> LF
<delim> LF
+ LF?
....
+
where `<delim>` is the chosen delimiter string. The string `<delim>`
immediately trailing `<raw>` is part of `<raw>`. This is one of
the limitations of the delimited format, it is impossible to supply
a data chunk which does not have an LF as its last byte.
++
+The `LF` after `<delim> LF` is optional (it used to be required).
`checkpoint`
~~~~~~~~~~~~
....
'checkpoint' LF
- LF
+ LF?
....
Note that fast-import automatically switches packfiles when the current
repository can be loaded into Git through fast-import in about 3 hours,
explicit checkpointing may not be necessary.
+The `LF` after the command is optional (it used to be required).
+
+`progress`
+~~~~~~~~~~
+Causes fast-import to print the entire `progress` line unmodified to
+its standard output channel (file descriptor 1) when the command is
+processed from the input stream. The command otherwise has no impact
+on the current import, or on any of fast-import's internal state.
+
+....
+ 'progress' SP <any> LF
+ LF?
+....
+
+The `<any>` part of the command may contain any sequence of bytes
+that does not contain `LF`. The `LF` after the command is optional.
+Callers may wish to process the output through a tool such as sed to
+remove the leading part of the line, for example:
+
+====
+ frontend | git-fast-import | sed 's/^progress //'
+====
+
+Placing a `progress` command immediately after a `checkpoint` will
+inform the reader when the `checkpoint` has been completed and it
+can safely access the refs that fast-import updated.
Tips and Tricks
---------------
Import Now, Repack Later
~~~~~~~~~~~~~~~~~~~~~~~~
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. Typically this takes only a very short time,
even for considerably large projects (100,000+ commits).
However repacking the repository is necessary to improve data
You only need to expend the effort once, and everyone using your
project will benefit from the smaller repository.
+Include Some Progress Messages
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Every once in a while have your frontend emit a `progress` message
+to fast-import. The contents of the messages are entirely free-form,
+so one suggestion would be to output the current month and year
+each time the current commit date moves into the next month.
+Your users will feel better knowing how much of the data stream
+has been processed.
+
Packfile Optimization
---------------------
------------------
There are a number of factors which affect how much memory fast-import
requires to perform an import. Like critical sections of core
-Git, fast-import uses its own memory allocators to ammortize any overheads
-associated with malloc. In practice fast-import tends to ammoritize any
+Git, fast-import uses its own memory allocators to amortize any overheads
+associated with malloc. In practice fast-import tends to amortize any
malloc overheads to 0, due to its use of large block allocations.
per object
~~~~~~~~~~~~~~~
Trees (aka directories) use just 12 bytes of memory on top of the
memory required for their entries (see ``per active file'' below).
-The cost of a tree is virtually 0, as its overhead ammortizes out
+The cost of a tree is virtually 0, as its overhead amortizes out
over the individual file entries.
per active file entry
GIT
---
Part of the gitlink:git[7] suite
-