As discovered by Ævar, we cannot increment graph version to
distinguish between generation numbers v1 and v2 [1]. Thus, one of
pre-requistes before implementing generation number v2 was to
distinguish between graph versions in a backwards compatible manner.
We are going to introduce a new chunk called Generation DATa chunk (or
GDAT). GDAT will store corrected committer date offsets whereas CDAT
will still store topological level.
Old Git does not understand GDAT chunk and would ignore it, reading
topological levels from CDAT. New Git can parse GDAT and take advantage
of newer generation numbers, falling back to topological levels when
GDAT chunk is missing (as it would happen with a commit-graph written
by old Git).
We introduce a test environment variable 'GIT_TEST_COMMIT_GRAPH_NO_GDAT'
which forces commit-graph file to be written without generation data
chunk to emulate a commit-graph file written by old Git.
To minimize the space required to store corrrected commit date, Git
stores corrected commit date offsets into the commit-graph file, instea
of corrected commit dates. This saves us 4 bytes per commit, decreasing
the GDAT chunk size by half, but it's possible for the offset to
overflow the 4-bytes allocated for storage. As such overflows are and
should be exceedingly rare, we use the following overflow management
scheme:
We introduce a new commit-graph chunk, Generation Data OVerflow ('GDOV')
to store corrected commit dates for commits with offsets greater than
GENERATION_NUMBER_V2_OFFSET_MAX.
If the offset is greater than GENERATION_NUMBER_V2_OFFSET_MAX, we set
the MSB of the offset and the other bits store the position of corrected
commit date in GDOV chunk, similar to how Extra Edge List is maintained.
We test the overflow-related code with the following repo history:
F - N - U
/ \
U - N - U N
\ /
N - F - N
Where the commits denoted by U have committer date of zero seconds
since Unix epoch, the commits denoted by N have committer date of
1112354055 (default committer date for the test suite) seconds since
Unix epoch and the commits denoted by F have committer date of
(2 ^ 31 - 2) seconds since Unix epoch.
The largest offset observed is 2 ^ 31, just large enough to overflow.
[1]: https://lore.kernel.org/git/87a7gdspo4.fsf@evledraar.gmail.com/
Signed-off-by: Abhishek Kumar <abhishekkumar8222@gmail.com>
Reviewed-by: Taylor Blau <me@ttaylorr.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
With most of preparations done, let's implement corrected commit date.
The corrected commit date for a commit is defined as:
* A commit with no parents (a root commit) has corrected commit date
equal to its committer date.
* A commit with at least one parent has corrected commit date equal to
the maximum of its commit date and one more than the largest corrected
commit date among its parents.
As a special case, a root commit with timestamp of zero (01.01.1970
00:00:00Z) has corrected commit date of one, to be able to distinguish
from GENERATION_NUMBER_ZERO (that is, an uncomputed corrected commit
date).
To minimize the space required to store corrected commit date, Git
stores corrected commit date offsets into the commit-graph file. The
corrected commit date offset for a commit is defined as the difference
between its corrected commit date and actual commit date.
Storing corrected commit date requires sizeof(timestamp_t) bytes, which
in most cases is 64 bits (uintmax_t). However, corrected commit date
offsets can be safely stored using only 32-bits. This halves the size
of GDAT chunk, which is a reduction of around 6% in the size of
commit-graph file.
However, using offsets be problematic if a commit is malformed but valid
and has committer date of 0 Unix time, as the offset would be the same
as corrected commit date and thus require 64-bits to be stored properly.
While Git does not write out offsets at this stage, Git stores the
corrected commit dates in member generation of struct commit_graph_data.
It will begin writing commit date offsets with the introduction of
generation data chunk.
Signed-off-by: Abhishek Kumar <abhishekkumar8222@gmail.com>
Reviewed-by: Taylor Blau <me@ttaylorr.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In a preparatory step for introducing corrected commit dates, let's
return timestamp_t values from commit_graph_generation(), use
timestamp_t for local variables and define GENERATION_NUMBER_INFINITY
as (2 ^ 63 - 1) instead.
We rename GENERATION_NUMBER_MAX to GENERATION_NUMBER_V1_MAX to
represent the largest topological level we can store in the commit data
chunk.
With corrected commit dates implemented, we will have two such *_MAX
variables to denote the largest offset and largest topological level
that can be stored.
Signed-off-by: Abhishek Kumar <abhishekkumar8222@gmail.com>
Reviewed-by: Taylor Blau <me@ttaylorr.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In a later commit we will introduce corrected commit date as the
generation number v2. Corrected commit dates will be stored in the new
seperate Generation Data chunk. However, to ensure backwards
compatibility with "Old" Git we need to continue to write generation
number v1 (topological levels) to the commit data chunk. Thus, we need
to compute and store both versions of generation numbers to write the
commit-graph file.
Therefore, let's introduce a commit-slab `topo_level_slab` to store
topological levels; corrected commit date will be stored in the member
`generation` of struct commit_graph_data.
The macros `GENERATION_NUMBER_INFINITY` and `GENERATION_NUMBER_ZERO`
mark commits not in the commit-graph file and commits written by a
version of Git that did not compute generation numbers respectively.
Generation numbers are computed identically for both kinds of commits.
A "slab-miss" should return `GENERATION_NUMBER_INFINITY` as the commit
is not in the commit-graph file. However, since the slab is
zero-initialized, it returns 0 (or rather `GENERATION_NUMBER_ZERO`).
Thus, we no longer need to check if the topological level of a commit is
`GENERATION_NUMBER_INFINITY`.
We will add a pointer to the slab in `struct write_commit_graph_context`
and `struct commit_graph` to populate the slab in
`fill_commit_graph_info` if the commit has a pre-computed topological
level as in case of split commit-graphs.
Signed-off-by: Abhishek Kumar <abhishekkumar8222@gmail.com>
Reviewed-by: Taylor Blau <me@ttaylorr.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In a preparatory step to implement generation number v2, we add tests to
ensure Git can read and parse commit-graph files without Generation Data
chunk. These files represent commit-graph files written by Old Git and
are neccesary for backward compatability.
We extend run_three_modes() and test_three_modes() to *_all_modes() with
the fourth mode being "commit-graph without generation data chunk".
Signed-off-by: Abhishek Kumar <abhishekkumar8222@gmail.com>
Reviewed-by: Taylor Blau <me@ttaylorr.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Both fill_commit_graph_info() and fill_commit_in_graph() parse
information present in commit data chunk. Let's simplify the
implementation by calling fill_commit_graph_info() within
fill_commit_in_graph().
fill_commit_graph_info() used to not load committer data from commit data
chunk. However, with the upcoming switch to using corrected committer
date as generation number v2, we will have to load committer date to
compute generation number value anyway.
e51217e15 (t5000: test tar files that overflow ustar headers,
30-06-2016) introduced a test 'generate tar with future mtime' that
creates a commit with committer date of (2^36 + 1) seconds since
EPOCH. The CDAT chunk provides 34-bits for storing committer date, thus
committer time overflows into generation number (within CDAT chunk) and
has undefined behavior.
The test used to pass as fill_commit_graph_info() would not set struct
member `date` of struct commit and load committer date from the object
database, generating a tar file with the expected mtime.
However, with corrected commit date, we will load the committer date
from CDAT chunk (truncated to lower 34-bits to populate the generation
number. Thus, Git sets date and generates tar file with the truncated
mtime.
The ustar format (the header format used by most modern tar programs)
only has room for 11 (or 12, depending on some implementations) octal
digits for the size and mtime of each file.
As the CDAT chunk is overflow by 12-octal digits but not 11-octal
digits, we split the existing tests to test both implementations
separately and add a new explicit test for 11-digit implementation.
To test the 11-octal digit implementation, we create a future commit
with committer date of 2^34 - 1, which overflows 11-octal digits without
overflowing 34-bits of the Commit Date chunks.
To test the 12-octal digit implementation, the smallest committer date
possible is 2^36 + 1, which overflows the CDAT chunk and thus
commit-graph must be disabled for the test.
Signed-off-by: Abhishek Kumar <abhishekkumar8222@gmail.com>
Reviewed-by: Taylor Blau <me@ttaylorr.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In indegree_walk_step(), we add unvisited parents to the indegree queue.
However, parents are not guaranteed to be parsed. As the indegree queue
sorts by generation number, let's parse parents before inserting them to
ensure the correct priority order.
Signed-off-by: Abhishek Kumar <abhishekkumar8222@gmail.com>
Reviewed-by: Taylor Blau <me@ttaylorr.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Before computing Bloom filters, the commit-graph machinery uses
commit_gen_cmp to sort commits by generation order for improved diff
performance. 3d11275505 (commit-graph: examine commits by generation
number, 2020-03-30) claims that this sort can reduce the time spent to
compute Bloom filters by nearly half.
But since c49c82aa4c (commit: move members graph_pos, generation to a
slab, 2020-06-17), this optimization is broken, since asking for a
'commit_graph_generation()' directly returns GENERATION_NUMBER_INFINITY
while writing.
Not all hope is lost, though: 'commit_gen_cmp()' falls back to
comparing commits by their date when they have equal generation number,
and so since c49c82aa4c is purely a date comparison function. This
heuristic is good enough that we don't seem to loose appreciable
performance while computing Bloom filters.
Applying this patch (compared with v2.30.0) speeds up computing Bloom
filters by factors ranging from 0.40% to 5.19% on various repositories [1].
So, avoid the useless 'commit_graph_generation()' while writing by
instead accessing the slab directly. This returns the newly-computed
generation numbers, and allows us to avoid the heuristic by directly
comparing generation numbers.
[1]: https://lore.kernel.org/git/20210105094535.GN8396@szeder.dev/
Signed-off-by: Abhishek Kumar <abhishekkumar8222@gmail.com>
Reviewed-by: Taylor Blau <me@ttaylorr.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Hotfix for a topic of this cycle.
* ma/maintenance-crontab-fix:
t7900-maintenance: test for magic markers
gc: fix handling of crontab magic markers
git-maintenance.txt: add missing word
Test coverage fix.
* js/no-more-prepare-for-main-in-test:
tests: drop the `PREPARE_FOR_MAIN_BRANCH` prereq
t9902: use `main` as initial branch name
t6302: use `main` as initial branch name
t5703: use `main` as initial branch name
t5510: use `main` as initial branch name
t5505: finalize transitioning to using the branch name `main`
t3205: finalize transitioning to using the branch name `main`
t3203: complete the transition to using the branch name `main`
t3201: finalize transitioning to using the branch name `main`
t3200: finish transitioning to the initial branch name `main`
t1400: use `main` as initial branch name
"git pack-redandant" when there is only one packfile used to crash,
which has been corrected.
* jx/pack-redundant-on-single-pack:
pack-redundant: fix crash when one packfile in repo
The 'linkgit' Asciidoc macro is misspelled as 'linkit' in the
description of 'GIT_SEQUENCE_EDITOR' since the addition of that variable
to git(1) in 902a126eca (doc: mention GIT_SEQUENCE_EDITOR and
'sequence.editor' more, 2020-08-31). Also, it uses two colons instead of
one.
Fix that.
Signed-off-by: Philippe Blain <levraiphilippeblain@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Comment did not adequately explain how the two loops work
together to achieve the goal of querying for matching of any
negative refspec.
Signed-off-by: Nipunn Koorapati <nipunn@dropbox.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The logic added to check for negative pathspec match by c0192df630
(refspec: add support for negative refspecs, 2020-09-30) looks at
refspec->src assuming it is never NULL, however when
remote.origin.push is set to ":", then refspec->src is NULL,
causing a segfault within strcmp.
Tell git to handle matching refspec by adding the needle to the
set of positively matched refspecs, since matching ":" refspecs
match anything as src.
Add test for matching refspec pushes fetch-negative-refspec
both individually and in combination with a negative refspec.
Signed-off-by: Nipunn Koorapati <nipunn@dropbox.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When we insert our "BEGIN" and "END" markers into the cron table, it's
so that a Git version from many years into the future would be able to
identify this region in the cron table. Let's add a test to make sure
that these markers don't ever change.
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Acked-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
On `git maintenance start`, we add a few entries to the user's cron
table. We wrap our entries using two magic markers, "# BEGIN GIT
MAINTENANCE SCHEDULE" and "# END GIT MAINTENANCE SCHEDULE". At a later
`git maintenance stop`, we will go through the table and remove these
lines. Or rather, we will remove the "BEGIN" marker, the "END" marker
and everything between them.
Alas, we have a bug in how we detect the "END" marker: we don't. As we
loop through all the lines of the crontab, if we are in the "old
region", i.e., the region we're aiming to remove, we make an early
`continue` and don't get as far as checking for the "END" marker. Thus,
once we've seen our "BEGIN", we remove everything until the end of the
file.
Rewrite the logic for identifying these markers. There are four cases
that are mutually exclusive: The current line starts a region or it ends
it, or it's firmly within the region, or it's outside of it (and should
be printed).
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Acked-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add a missing "a" before "bunch".
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Acked-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This fixes a segmentation fault.
The bug is caused by dereferencing `new_branch_info->commit` when it is
`NULL`, which is the case when the tree-ish argument is actually a tree,
not a commit-ish. This was introduced in 5602b500c3 (builtin/checkout:
fix `git checkout -p HEAD...` bug, 2020-10-07), where we tried to ensure
that the special tree-ish `HEAD...` is handled correctly.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
* github/master: (42 commits)
Git 2.30-rc1
git-gui: use gray background for inactive text widgets
Another batch before 2.30-rc1
git-gui: Fix selected text colors
Makefile: conditionally include GIT-VERSION-FILE
git-gui: fix colored label backgrounds when using themed widgets
config.mak.uname: remove old NonStop compatibility settings
diff: correct interaction between --exit-code and -I<pattern>
t/perf: fix test_export() failure with BSD `sed`
style: do not "break" in switch() after "return"
compat-util: pretend that stub setitimer() always succeeds
strmap: make callers of strmap_remove() to call it in void context
doc: mention Python 3.x supports
index-format.txt: document v2 format of file system monitor extension
docs: multi-pack-index: remove note about future 'verify' work
init: provide useful advice about init.defaultBranch
get_default_branch_name(): prepare for showing some advice
branch -m: allow renaming a yet-unborn branch
init: document `init.defaultBranch` better
t7900: use --fixed-value in git-maintenance tests
...
"git diff -I<pattern> -exit-code" should exit with 0 status when
all the changes match the ignored pattern, but it didn't.
* jc/diff-I-status-fix:
diff: correct interaction between --exit-code and -I<pattern>
Our users are going to be trained to prepare for future change of
init.defaultBranch configuration variable.
* js/init-defaultbranch-advice:
init: provide useful advice about init.defaultBranch
get_default_branch_name(): prepare for showing some advice
branch -m: allow renaming a yet-unborn branch
init: document `init.defaultBranch` better
