Merge branch 'master' of git://repo.or.cz/git/fastimport
* 'master' of git://repo.or.cz/git/fastimport:
Add a Tips and Tricks section to fast-import's manual.
Don't crash fast-import if the marks cannot be exported.
Dump all refs and marks during a checkpoint in fast-import.
Teach fast-import how to sit quietly in the corner.
Teach fast-import how to clear the internal branch content.
Minor timestamp related documentation corrections for fast-import.
Frontends can use this file to validate imports after they
have been completed.
--quiet::
Disable all non-fatal output, making gfi silent when it
is successful. This option disables the output shown by
\--stats.
--stats::
Display some basic statistics about the objects gfi has
created, the packfiles they were stored into, and the
memory used by gfi during this run. Showing this output
is currently the default, but can be disabled with \--quiet.
Performance
-----------
The design of gfi allows it to import large projects in a minimum
@ -106,8 +118,8 @@ fast-forward update, gfi will skip updating that ref and instead
@@ -106,8 +118,8 @@ fast-forward update, gfi will skip updating that ref and instead
prints a warning message. gfi will always attempt to update all
branch refs, and does not stop on the first failure.
Branch updates can be forced with `--force`, but its recommended that
this only be used on an otherwise quiet repository. Using `--force`
Branch updates can be forced with \--force, but its recommended that
this only be used on an otherwise quiet repository. Using \--force
is not necessary for an initial import into an empty repository.
@ -148,26 +160,28 @@ Date Formats
@@ -148,26 +160,28 @@ Date Formats
~~~~~~~~~~~~
The following date formats are supported. A frontend should select
the format it will use for this import by passing the format name
in the `--date-format=<fmt>` command line option.
in the \--date-format=<fmt> command line option.
`raw`::
This is the Git native format and is `<time> SP <tz>`.
It is also gfi's default format, if `--date-format` was
This is the Git native format and is `<time> SP <offutc>`.
It is also gfi's default format, if \--date-format was
not specified.
+
The time of the event is specified by `<time>` as the number of
seconds since the UNIX epoch (midnight, Jan 1, 1970, UTC) and is
written as an ASCII decimal integer.
+
The timezone is specified by `<tz>` as a positive or negative offset
from UTC. For example EST (which is typically 5 hours behind GMT)
would be expressed in `<tz>` by ``-0500'' while GMT is ``+0000''.
The local offset is specified by `<offutc>` as a positive or negative
offset from UTC. For example EST (which is 5 hours behind UTC)
would be expressed in `<tz>` by ``-0500'' while UTC is ``+0000''.
The local offset does not affect `<time>`; it is used only as an
advisement to help formatting routines display the timestamp.
+
If the timezone is not available in the source material, use
``+0000'', or the most common local timezone. For example many
If the local offset is not available in the source material, use
``+0000'', or the most common local offset. For example many
organizations have a CVS repository which has only ever been accessed
by users who are located in the same location and timezone. In this
case the user's timezone can be easily assumed.
case the offset from UTC can be easily assumed.
+
Unlike the `rfc2822` format, this format is very strict. Any
variation in formatting will cause gfi to reject the value.
@ -186,6 +200,11 @@ the malformed string. There are also some types of malformed
@@ -186,6 +200,11 @@ the malformed string. There are also some types of malformed
strings which Git will parse wrong, and yet consider valid.
Seriously malformed strings will be rejected.
+
Unlike the `raw` format above, the timezone/UTC offset information
contained in an RFC 2822 date string is used to adjust the date
value to UTC prior to storage. Therefore it is important that
this information be as accurate as possible.
+
If the source material is formatted in RFC 2822 style dates,
the frontend should let gfi handle the parsing and conversion
(rather than attempting to do it itself) as the Git parser has
@ -262,7 +281,7 @@ change to the project.
@@ -262,7 +281,7 @@ change to the project.
data
('from' SP <committish> LF)?
('merge' SP <committish> LF)?
(filemodify | filedelete)*
(filemodify | filedelete | filedeleteall)*
LF
....
@ -285,10 +304,12 @@ commit message use a 0 length data. Commit messages are free-form
@@ -285,10 +304,12 @@ commit message use a 0 length data. Commit messages are free-form
and are not interpreted by Git. Currently they must be encoded in
UTF-8, as gfi does not permit other encodings to be specified.
Zero or more `filemodify` and `filedelete` commands may be
included to update the contents of the branch prior to the commit.
These commands can be supplied in any order, gfi is not sensitive
to pathname or operation ordering.
Zero or more `filemodify`, `filedelete` 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`
wipes the branch clean (see below).
`author`
^^^^^^^^
@ -312,7 +333,7 @@ the email address from the other fields in the line. Note that
@@ -312,7 +333,7 @@ the email address from the other fields in the line. Note that
`LT` and `LF`. It is typically UTF-8 encoded.
The time of the change is specified by `<when>` using the date format
that was selected by the `--date-format=<fmt>` command line option.
that was selected by the \--date-format=<fmt> command line option.
See ``Date Formats'' above for the set of supported formats, and
their syntax.
@ -452,6 +473,30 @@ first non-empty directory or the root is reached.
@@ -452,6 +473,30 @@ first non-empty directory or the root is reached.
here `<path>` is the complete path of the file to be removed.
See `filemodify` above for a detailed description of `<path>`.
`filedeleteall`
^^^^^^^^^^^^^^^
Included in a `commit` command to remove all files (and also all
directories) from the branch. This command resets the internal
branch structure to have no files in it, allowing the frontend
to subsequently add all interesting files from scratch.
....
'deleteall' LF
....
This command is extremely useful if the frontend does not know
(or does not care to know) what files are currently on the branch,
and therefore cannot generate the proper `filedelete` commands to
update the content.
Issuing a `filedeleteall` followed by the needed `filemodify`
commands to set the correct content will produce the same results
as sending only the needed `filemodify` and `filedelete` commands.
The `filedeleteall` approach may however require gfi to use slightly
more memory per active branch (less than 1 MiB for even most large
projects); so frontends that can easily obtain only the affected
paths for a commit are encouraged to do so.
`mark`
~~~~~~
Arranges for gfi to save a reference to the current object, allowing
@ -605,17 +650,117 @@ a data chunk which does not have an LF as its last byte.
@@ -605,17 +650,117 @@ a data chunk which does not have an LF as its last byte.
`checkpoint`
~~~~~~~~~~~~
Forces gfi to close the current packfile and start a new one.
As this requires a significant amount of CPU time and disk IO
(to compute the overall pack SHA-1 checksum and generate the
corresponding index file) it can easily take several minutes for
a single `checkpoint` command to complete.
Forces gfi to close the current packfile, start a new one, and to
save out all current branch refs, tags and marks.
....
'checkpoint' LF
LF
....
Note that gfi automatically switches packfiles when the current
packfile reaches \--max-pack-size, or 4 GiB, whichever limit is
smaller. During an automatic packfile switch gfi does not update
the branch refs, tags or marks.
As a `checkpoint` can require a significant amount of CPU time and
disk IO (to compute the overall pack SHA-1 checksum, generate the
corresponding index file, and update the refs) it can easily take
several minutes for a single `checkpoint` command to complete.
Frontends may choose to issue checkpoints during extremely large
and long running imports, or when they need to allow another Git
process access to a branch. However given that a 30 GiB Subversion
repository can be loaded into Git through gfi in about 3 hours,
explicit checkpointing may not be necessary.
Tips and Tricks
---------------
The following tips and tricks have been collected from various
users of gfi, and are offered here as suggestions.
Use One 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
line. gfi will dump a file which lists every mark and the Git
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
accuracy and completeness of the import by comparing each Git
commit to the corresponding source revision.
Coming from a system such as Perforce or Subversion this should be
quite simple, as the gfi mark can also be the Perforce changeset
number or the Subversion revision number.
Freely Skip Around Branches
~~~~~~~~~~~~~~~~~~~~~~~~~~~
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
faster for gfi, it tends to increase the complexity of the frontend
code considerably.
The branch LRU builtin to gfi tends to behave very well, and the
cost of activating an inactive branch is so low that bouncing around
between branches has virtually no impact on import performance.
Use Tag Fixup Branches
~~~~~~~~~~~~~~~~~~~~~~
Some other SCM systems let the user create a tag from multiple
files which are not from the same commit/changeset. Or to create
tags which are a subset of the files available in the repository.
Importing these tags as-is in Git is impossible without making at
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
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
dummy branch.
For example since all normal branches are stored under `refs/heads/`
name the tag fixup branch `TAG_FIXUP`. This way it is impossible for
the fixup branch used by the importer to have namespace conflicts
with real branches imported from the source (the name `TAG_FIXUP`
is not `refs/heads/TAG_FIXUP`).
When committing fixups, consider using `merge` to connect the
commit(s) which are supplying file revisions to the fixup branch.
Doing so will allow tools such as gitlink:git-blame[1] to track
through the real commit history and properly annotate the source
files.
After gfi terminates the frontend will need to do `rm .git/TAG_FIXUP`
to remove the dummy branch.
Import Now, Repack Later
~~~~~~~~~~~~~~~~~~~~~~~~
As soon as gfi completes the Git repository is completely valid
and ready for use. Typicallly this takes only a very short time,
even for considerably large projects (100,000+ commits).
However repacking the repository is necessary to improve data
locality and access performance. It can also take hours on extremely
large projects (especially if -f and a large \--window parameter is
used). Since repacking is safe to run alongside readers and writers,
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!
If you choose to wait for the repack, don't try to run benchmarks
or performance tests until repacking is completed. gfi outputs
suboptimal packfiles that are simply never seen in real use
situations.
Repacking Historical Data
~~~~~~~~~~~~~~~~~~~~~~~~~
If you are repacking very old imported data (e.g. older than the
last year), consider expending some extra CPU time and supplying
\--window=50 (or higher) when you run gitlink:git-repack[1].
This will take longer, but will also produce a smaller packfile.
You only need to expend the effort once, and everyone using your
project will benefit from the smaller repository.
Packfile Optimization
---------------------
When packing a blob gfi always attempts to deltify against the last
@ -646,6 +791,7 @@ deltas are suboptimal (see above) then also adding the `-f` option
@@ -646,6 +791,7 @@ deltas are suboptimal (see above) then also adding the `-f` option
to force recomputation of all deltas can significantly reduce the
final packfile size (30-50% smaller can be quite typical).
Memory Utilization
------------------
There are a number of factors which affect how much memory gfi
@ -702,7 +848,7 @@ branch, their in-memory storage size can grow to a considerable size
@@ -702,7 +848,7 @@ branch, their in-memory storage size can grow to a considerable size
gfi automatically moves active branches to inactive status based on
a simple least-recently-used algorithm. The LRU chain is updated on
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=.
Junio C Hamano
18 years ago