ref_newer() builds a commit_list to pass a single potential ancestor to
is_descendant_of(). The latter leaves the list intact. Release the
allocated memory after the call.
Signed-off-by: René Scharfe <l.s.r@web.de>
Acked-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The repo_is_descendant_of() method is aware of the existence of the
commit-graph file. It checks for generation_numbers_enabled() before
deciding on using can_all_from_reach() or repo_in_merge_bases()
depending on the situation. The reason here is that can_all_from_reach()
uses a depth-first search that is limited by the minimum generation
number of the target commits, and that algorithm can be very slow when
generation numbers are not present. The alternative uses
paint_down_to_common() which will walk the entire merge-base boundary,
which is typically slower.
This method is used by commands like "git tag --contains" and "git
branch --contains" for very fast results when a commit-graph file
exists. Unfortunately, it is _not_ used in commands like "git merge-base
--is-ancestor" which is doing an even simpler request.
This issue was raised recently [1] with respect to a change to how
generation numbers are stored, but was also reported much earlier [2]
before commit-reach.c existed to simplify these reachability queries.
[1] https://lore.kernel.org/git/20200607195347.GA8232@szeder.dev/
[2] https://lore.kernel.org/git/87608bawoa.fsf@evledraar.gmail.com/
The root cause is that builtin/merge-base.c has a method
handle_is_ancestor() that calls in_merge_bases(), an older version of
repo_in_merge_bases(). It would be better if we have every caller to
in_merge_bases() use the logic in can_all_from_reach() when possible.
This is where things get a little tricky: repo_is_descendant_of() calls
repo_in_merge_bases() in the non-generation numbers enabled case! If we
simply update repo_in_merge_bases() to call repo_is_descendant_of()
instead of repo_in_merge_bases_many(), then we will get a recursive call
loop. Thankfully, this is caught by the test suite in the default mode
(i.e. GIT_TEST_COMMIT_GRAPH=0).
The trick, then, is to make the non-generation number case for
repo_is_descendant_of() call repo_in_merge_bases_many() directly,
skipping the non-_many version. This allows us to take advantage of this
faster code path, when possible.
The easiest way to measure the performance impact is to test the
following command on the Linux kernel repository:
git merge-base --is-ancestor <A> <B>
| A | B | Time Before | Time After |
|------|------|-------------|------------|
| v3.0 | v5.7 | 0.459s | 0.028s |
| v4.0 | v5.7 | 0.267s | 0.021s |
| v5.0 | v5.7 | 0.074s | 0.013s |
Note that each of these samples return success. The old code performed
the same operation when <A> and <B> are swapped. However,
can_all_from_reach() will return immediately if the generation numbers
show that <A> has larger generation number than <B>. Thus, the time for
the swapped case is universally 0.004s in each case.
Reported-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Reported-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The next change will make repo_in_merge_bases() depend on the logic in
is_descendant_of(), but we need to make the method independent of
the_repository first.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The previous commit includes a failing test for an issue around
fetch.writeCommitGraph and fetching in a repo with a submodule. Here, we
fix that bug and set the test to "test_expect_success".
The problem arises with this set of commands when the remote repo at
<url> has a submodule. Note that --recurse-submodules is not needed to
demonstrate the bug.
$ git clone <url> test
$ cd test
$ git -c fetch.writeCommitGraph=true fetch origin
Computing commit graph generation numbers: 100% (12/12), done.
BUG: commit-graph.c:886: missing parent <hash1> for commit <hash2>
Aborted (core dumped)
As an initial fix, I converted the code in builtin/fetch.c that calls
write_commit_graph_reachable() to instead launch a "git commit-graph
write --reachable --split" process. That code worked, but is not how we
want the feature to work long-term.
That test did demonstrate that the issue must be something to do with
internal state of the 'git fetch' process.
The write_commit_graph() method in commit-graph.c ensures the commits we
plan to write are "closed under reachability" using close_reachable().
This method walks from the input commits, and uses the UNINTERESTING
flag to mark which commits have already been visited. This allows the
walk to take O(N) time, where N is the number of commits, instead of
O(P) time, where P is the number of paths. (The number of paths can be
exponential in the number of commits.)
However, the UNINTERESTING flag is used in lots of places in the
codebase. This flag usually means some barrier to stop a commit walk,
such as in revision-walking to compare histories. It is not often
cleared after the walk completes because the starting points of those
walks do not have the UNINTERESTING flag, and clear_commit_marks() would
stop immediately.
This is happening during a 'git fetch' call with a remote. The fetch
negotiation is comparing the remote refs with the local refs and marking
some commits as UNINTERESTING.
I tested running clear_commit_marks_many() to clear the UNINTERESTING
flag inside close_reachable(), but the tips did not have the flag, so
that did nothing.
It turns out that the calculate_changed_submodule_paths() method is at
fault. Thanks, Peff, for pointing out this detail! More specifically,
for each submodule, the collect_changed_submodules() runs a revision
walk to essentially do file-history on the list of submodules. That
revision walk marks commits UNININTERESTING if they are simplified away
by not changing the submodule.
Instead, I finally arrived on the conclusion that I should use a flag
that is not used in any other part of the code. In commit-reach.c, a
number of flags were defined for commit walk algorithms. The REACHABLE
flag seemed like it made the most sense, and it seems it was not
actually used in the file. The REACHABLE flag was used in early versions
of commit-reach.c, but was removed by 4fbcca4 (commit-reach: make
can_all_from_reach... linear, 2018-07-20).
Add the REACHABLE flag to commit-graph.c and use it instead of
UNINTERESTING in close_reachable(). This fixes the bug in manual
testing.
Reported-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Helped-by: Jeff King <peff@peff.net>
Helped-by: Szeder Gábor <szeder.dev@gmail.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The in-core repository instances are passed through more codepaths.
* sb/more-repo-in-api: (23 commits)
t/helper/test-repository: celebrate independence from the_repository
path.h: make REPO_GIT_PATH_FUNC repository agnostic
commit: prepare free_commit_buffer and release_commit_memory for any repo
commit-graph: convert remaining functions to handle any repo
submodule: don't add submodule as odb for push
submodule: use submodule repos for object lookup
pretty: prepare format_commit_message to handle arbitrary repositories
commit: prepare logmsg_reencode to handle arbitrary repositories
commit: prepare repo_unuse_commit_buffer to handle any repo
commit: prepare get_commit_buffer to handle any repo
commit-reach: prepare in_merge_bases[_many] to handle any repo
commit-reach: prepare get_merge_bases to handle any repo
commit-reach.c: allow get_merge_bases_many_0 to handle any repo
commit-reach.c: allow remove_redundant to handle any repo
commit-reach.c: allow merge_bases_many to handle any repo
commit-reach.c: allow paint_down_to_common to handle any repo
commit: allow parse_commit* to handle any repo
object: parse_object to honor its repository argument
object-store: prepare has_{sha1, object}_file to handle any repo
object-store: prepare read_object_file to deal with any repo
...
Similarly to previous patches, the get_merge_base functions are used
often in the code base, which makes migrating them hard.
Implement the new functions, prefixed with 'repo_' and hide the old
functions behind a wrapper macro.
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
As the function is file local and not widely used, migrate it all at once.
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The existing reachability algorithms in commit-reach.c focus on
finding merge-bases or determining if all commits in a set X can
reach at least one commit in a set Y. However, for two commits sets
X and Y, we may also care about which commits in Y are reachable
from at least one commit in X.
Implement get_reachable_subset() which answers this question. Given
two arrays of commits, 'from' and 'to', return a commit_list with
every commit from the 'to' array that is reachable from at least
one commit in the 'from' array.
The algorithm is a simple walk starting at the 'from' commits, using
the PARENT2 flag to indicate "this commit has already been added to
the walk queue". By marking the 'to' commits with the PARENT1 flag,
we can determine when we see a commit from the 'to' array. We remove
the PARENT1 flag as we add that commit to the result list to avoid
duplicates.
The order of the resulting list is a reverse of the order that the
commits are discovered in the walk.
There are a couple shortcuts to avoid walking more than we need:
1. We determine the minimum generation number of commits in the
'to' array. We do not walk commits with generation number
below this minimum.
2. We count how many distinct commits are in the 'to' array, and
decrement this count when we discover a 'to' commit during the
walk. If this number reaches zero, then we can terminate the
walk.
Tests will be added using the 'test-tool reach' helper in a
subsequent commit.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The elements of the array to be sorted are commit pointers, so the
comparison function gets handed references to these pointers, not
pointers to commit objects. Cast to the right type and dereference
once to correctly get the commit reference.
Found using Clang's ASan and t5500.
Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The algorithm in can_all_from_reach_with_flags() performs a depth-
first-search, terminated by generation number, intending to use
a hueristic that "important" commits are found in the first-parent
history. This heuristic is valuable in scenarios like fetch
negotiation.
However, there is a problem! After the search finds a target commit,
it should pop all commits off the stack and mark them as "can reach".
This logic is incorrect, so the algorithm instead walks all reachable
commits above the generation-number cutoff.
The existing algorithm is still an improvement over the previous
algorithm, as the worst-case complexity went from quadratic to linear.
The performance measurement at the time was good, but not dramatic.
By fixing this heuristic, we reduce the number of walked commits.
We can also re-run the performance tests from commit 4fbcca4e
"commit-reach: make can_all_from_reach... linear".
Performance was measured on the Linux repository using
'test-tool reach can_all_from_reach'. The input included rows seeded by
tag values. The "small" case included X-rows as v4.[0-9]* and Y-rows as
v3.[0-9]*. This mimics a (very large) fetch that says "I have all major
v3 releases and want all major v4 releases." The "large" case included
X-rows as "v4.*" and Y-rows as "v3.*". This adds all release-candidate
tags to the set, which does not greatly increase the number of objects
that are considered, but does increase the number of 'from' commits,
demonstrating the quadratic nature of the previous code.
Small Case:
4fbcca4e~1: 0.85 s
4fbcca4e: 0.26 s (num_walked: 1,011,035)
HEAD: 0.14 s (num_walked: 8,601)
Large Case:
4fbcca4e~1: 24.0 s
4fbcca4e: 0.12 s (num_walked: 503,925)
HEAD: 0.06 s (num_walked: 217,243)
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We added faster equality-comparison functions for hashes in
14438c4497 (introduce hasheq() and oideq(), 2018-08-28). A
few topics were in-flight at the time, and can now be
converted. This covers all spots found by "make coccicheck"
in master (the coccicheck results were tweaked by hand for
style).
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Due to a regression introduced by 4fbcca4e "commit-reach: make
can_all_from_reach... linear" the series including b67f6b26
"commit-reach: properly peel tags" was merged to master quickly.
There were a few more cleanups left to apply in the series, which
are included by this change:
1. Clean up a comment that is in the incorrect style.
2. Replace multiple calls to clear_commit_marks() with one call to
clear_commit_marks_many().
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Recent update broke the reachability algorithm when refs (e.g.
tags) that point at objects that are not commit were involved,
which has been fixed.
* ds/reachable:
commit-reach: fix memory and flag leaks
commit-reach: properly peel tags
The can_all_from_reach_with_flag() method uses 'assign_flag' as a
value we can use to mark objects temporarily during our commit walk.
The intent is that these flags are removed from all objects before
returning. However, this is not the case.
The 'from' array could also contain objects that are not commits, and
we mark those objects with 'assign_flag'. Add a loop to the 'cleanup'
section that removes these markers.
Also, we forgot to free() the memory for 'list', so add that to the
'cleanup' section.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The can_all_from_reach_with_flag() algorithm was refactored in 4fbcca4e
"commit-reach: make can_all_from_reach... linear" but incorrectly
assumed that all objects provided were commits. During a fetch
negotiation, ok_to_give_up() in upload-pack.c may provide unpeeled tags
to the 'from' array. The current code creates a segfault.
Add a direct call to can_all_from_reach_with_flag() in 'test-tool reach'
and add a test in t6600-test-reach.sh that demonstrates this segfault.
Correct the issue by peeling tags when investigating the initial list
of objects in the 'from' array.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The code for computing history reachability has been shuffled,
obtained a bunch of new tests to cover them, and then being
improved.
* ds/reachable:
commit-reach: correct accidental #include of C file
commit-reach: use can_all_from_reach
commit-reach: make can_all_from_reach... linear
commit-reach: replace ref_newer logic
test-reach: test commit_contains
test-reach: test can_all_from_reach_with_flags
test-reach: test reduce_heads
test-reach: test get_merge_bases_many
test-reach: test is_descendant_of
test-reach: test in_merge_bases
test-reach: create new test tool for ref_newer
commit-reach: move can_all_from_reach_with_flags
upload-pack: generalize commit date cutoff
upload-pack: refactor ok_to_give_up()
upload-pack: make reachable() more generic
commit-reach: move commit_contains from ref-filter
commit-reach: move ref_newer from remote.c
commit.h: remove method declarations
commit-reach: move walk methods from commit.c
Without this change, the build breaks with clang:
libgit/ref-filter.pic.o: multiple definition of 'filter_refs'
libgit/commit-reach.pic.o: previous definition here
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The is_descendant_of method previously used in_merge_bases() to check if
the commit can reach any of the commits in the provided list. This had
two performance problems:
1. The performance is quadratic in worst-case.
2. A single in_merge_bases() call requires walking beyond the target
commit in order to find the full set of boundary commits that may be
merge-bases.
The can_all_from_reach method avoids this quadratic behavior and can
limit the search beyond the target commits using generation numbers. It
requires a small prototype adjustment to stop using commit-date as a
cutoff, as that optimization is no longer appropriate here.
Since in_merge_bases() uses paint_down_to_common(), is_descendant_of()
naturally found cutoffs to avoid walking the entire commit graph. Since
we want to always return the correct result, we cannot use the
min_commit_date cutoff in can_all_from_reach. We then rely on generation
numbers to provide the cutoff.
Since not all repos will have a commit-graph file, nor will we always
have generation numbers computed for a commit-graph file, create a new
method, generation_numbers_enabled(), that checks for a commit-graph
file and sees if the first commit in the file has a non-zero generation
number. In the case that we do not have generation numbers, use the old
logic for is_descendant_of().
Performance was meausured on a copy of the Linux repository using the
'test-tool reach is_descendant_of' command using this input:
A:v4.9
X:v4.10
X:v4.11
X:v4.12
X:v4.13
X:v4.14
X:v4.15
X:v4.16
X:v4.17
X.v3.0
Note that this input is tailored to demonstrate the quadratic nature of
the previous method, as it will compute merge-bases for v4.9 versus all
of the later versions before checking against v4.1.
Before: 0.26 s
After: 0.21 s
Since we previously used the is_descendant_of method in the ref_newer
method, we also measured performance there using
'test-tool reach ref_newer' with this input:
A:v4.9
B:v3.19
Before: 0.10 s
After: 0.08 s
By adding a new commit with parent v3.19, we test the non-reachable case
of ref_newer:
Before: 0.09 s
After: 0.08 s
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The can_all_from_reach_with_flags() algorithm is currently quadratic in
the worst case, because it calls the reachable() method for every 'from'
without tracking which commits have already been walked or which can
already reach a commit in 'to'.
Rewrite the algorithm to walk each commit a constant number of times.
We also add some optimizations that should work for the main consumer of
this method: fetch negotitation (haves/wants).
The first step includes using a depth-first-search (DFS) from each
'from' commit, sorted by ascending generation number. We do not walk
beyond the minimum generation number or the minimum commit date. This
DFS is likely to be faster than the existing reachable() method because
we expect previous ref values to be along the first-parent history.
If we find a target commit, then we mark everything in the DFS stack as
a RESULT. This expands the set of targets for the other 'from' commits.
We also mark the visited commits using 'assign_flag' to prevent re-
walking the same commits.
We still need to clear our flags at the end, which is why we will have a
total of three visits to each commit.
Performance was measured on the Linux repository using
'test-tool reach can_all_from_reach'. The input included rows seeded by
tag values. The "small" case included X-rows as v4.[0-9]* and Y-rows as
v3.[0-9]*. This mimics a (very large) fetch that says "I have all major
v3 releases and want all major v4 releases." The "large" case included
X-rows as "v4.*" and Y-rows as "v3.*". This adds all release-candidate
tags to the set, which does not greatly increase the number of objects
that are considered, but does increase the number of 'from' commits,
demonstrating the quadratic nature of the previous code.
Small Case:
Before: 1.52 s
After: 0.26 s
Large Case:
Before: 3.50 s
After: 0.27 s
Note how the time increases between the two cases in the two versions.
The new code increases relative to the number of commits that need to be
walked, but not directly relative to the number of 'from' commits.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The ref_newer method is used by 'git push' to check if a force-push is
required. This method does not use any kind of cutoff when walking, so
in the case of a force-push will walk all reachable commits.
The is_descendant_of method already uses paint_down_to_common along with
cutoffs. By translating the ref_newer arguments into the commit and
commit_list required by is_descendant_of, we can have one fewer commit
walk and also improve our performance!
For a copy of the Linux repository, 'test-tool reach ref_newer' presents
the following improvements with the specified input. In the case that
ref_newer returns 1, there is no improvement. The improvement is in the
second case where ref_newer returns 0.
Input:
A:v4.9
B:v3.19
Before: 0.09 s
After: 0.09 s
To test the negative case, add a new commit with parent v3.19,
regenerate the commit-graph, and then run with B pointing at that
commit.
Before: 0.43 s
After: 0.09 s
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The can_all_from_reach_with_flags method is used by ok_to_give_up in
upload-pack.c to see if we have done enough negotiation during a fetch.
This method is intentionally created to preserve state between calls to
assist with stateful negotiation, such as over SSH.
To make this method testable, add a new can_all_from_reach method that
does the initial setup and final tear-down. We will later use this
method in production code. Call the method from 'test-tool reach' for
now.
Since this is a many-to-many reachability query, add a new type of input
to the 'test-tool reach' input format. Lines "Y:<committish>" create a
list of commits to be the reachability targets from the commits in the
'X' list. In the context of fetch negotiation, the 'X' commits are the
'want' commits and the 'Y' commits are the 'have' commits.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
There are several commit walks in the codebase. Group them together into
a new commit-reach.c file and corresponding header. After we group these
walks into one place, we can reduce duplicate logic by calling
equivalent methods.
The can_all_from_reach_with_flags method is used in a stateful way by
upload-pack.c. The parameters are very flexible, so we will be able to
use its commit walking logic for many other callers.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
There are several commit walks in the codebase. Group them together into
a new commit-reach.c file and corresponding header. After we group these
walks into one place, we can reduce duplicate logic by calling
equivalent methods.
All methods are direct moves, except we also make the commit_contains()
method public so its consumers in ref-filter.c can still call it. We can
also test this method in a test-tool in a later commit.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
There are several commit walks in the codebase. Group them together into
a new commit-reach.c file and corresponding header. After we group these
walks into one place, we can reduce duplicate logic by calling
equivalent methods.
The ref_newer() method is used by 'git push -f' to check if a force-push
is necessary. By making the method public, we make it possible to test
the method directly without setting up an envieronment where a 'git
push' call makes sense.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
There are several commit walks in the codebase. Group them together into
a new commit-reach.c file and corresponding header. After we group these
walks into one place, we can reduce duplicate logic by calling
equivalent methods.
The method declarations in commit.h are not touched by this commit and
will be moved in a following commit. Many consumers need to point to
commit-reach.h and that would bloat this commit.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
