"git merge-base" in 2.19-rc1 has performance regression when the
(experimental) commit-graph feature is in use, which has been
mitigated.
* ds/commit-graph-lockfile-fix:
commit: don't use generation numbers if not needed
In 3afc679b "commit: use generations in paint_down_to_common()",
the queue in paint_down_to_common() was changed to use a priority
order based on generation number before commit date. This served
two purposes:
1. When generation numbers are present, the walk guarantees
correct topological relationships, regardless of clock skew in
commit dates.
2. It enables short-circuiting the walk when the min_generation
parameter is added in d7c1ec3e "commit: add short-circuit to
paint_down_to_common()". This short-circuit helps commands
like 'git branch --contains' from needing to walk to a merge
base when we know the result is false.
The commit message for 3afc679b includes the following sentence:
This change does not affect the number of commits that are
walked during the execution of paint_down_to_common(), only
the order that those commits are inspected.
This statement is incorrect. Because it changes the order in which
the commits are inspected, it changes the order they are added to
the queue, and hence can change the number of loops before the
queue_has_nonstale() method returns true.
This change makes a concrete difference depending on the topology
of the commit graph. For instance, computing the merge-base between
consecutive versions of the Linux kernel has no effect for versions
after v4.9, but 'git merge-base v4.8 v4.9' presents a performance
regression:
v2.18.0: 0.122s
v2.19.0-rc1: 0.547s
HEAD: 0.127s
To determine that this was simply an ordering issue, I inserted
a counter within the while loop of paint_down_to_common() and
found that the loop runs 167,468 times in v2.18.0 and 635,579
times in v2.19.0-rc1.
The topology of this case can be described in a simplified way
here:
v4.9
| \
| \
v4.8 \
| \ \
| \ |
... A B
| / /
| / /
|/__/
C
Here, the "..." means "a very long line of commits". By generation
number, A and B have generation one more than C. However, A and B
have commit date higher than most of the commits reachable from
v4.8. When the walk reaches v4.8, we realize that it has PARENT1
and PARENT2 flags, so everything it can reach is marked as STALE,
including A. B has only the PARENT1 flag, so is not STALE.
When paint_down_to_common() is run using
compare_commits_by_commit_date, A and B are removed from the queue
early and C is inserted into the queue. At this point, C and the
rest of the queue entries are marked as STALE. The loop then
terminates.
When paint_down_to_common() is run using
compare_commits_by_gen_then_commit_date, B is removed from the
queue only after the many commits reachable from v4.8 are explored.
This causes the loop to run longer. The reason for this regression
is simple: the queue order is intended to not explore a commit
until everything that _could_ reach that commit is explored. From
the information gathered by the original ordering, we have no
guarantee that there is not a commit D reachable from v4.8 that
can also reach B. We gained absolute correctness in exchange for
a performance regression.
The performance regression is probably the worse option, since
these incorrect results in paint_down_to_common() are rare. The
topology required for the performance regression are less rare,
but still require multiple merge commits where the parents differ
greatly in generation number. In our example above, the commit A
is as important as the commit B to demonstrate the problem, since
otherwise the commit C will sit in the queue as non-stale just as
long in both orders.
The solution provided uses the min_generation parameter to decide
if we should use generation numbers in our ordering. When
min_generation is equal to zero, it means that the caller has no
known cutoff for the walk, so we should rely on our commit-date
heuristic as before; this is the case with merge_bases_many().
When min_generation is non-zero, then the caller knows a valuable
cutoff for the short-circuit mechanism; this is the case with
remove_redundant() and in_merge_bases_many().
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The author_date_slab is used to store the author date of a commit
when walking with the --author-date flag in rev-list or log. This
was added as an 'unsigned long' in
81c6b38b "log: --author-date-order"
Since 'unsigned long' is ambiguous in its bit-ness across platforms
(64-bit in Linux, 32-bit in Windows, for example), most references
to the author dates in commit.c were converted to timestamp_t in
dddbad72 "timestamp_t: a new data type for timestamps"
However, the slab definition was missed, leading to a mismatch in
the data types in Windows. This would not reveal itself as a bug
unless someone authors a commit after February 2106, but commits
can store anything as their author date.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
"git fsck" learns to make sure the optional commit-graph file is in
a sane state.
* ds/commit-graph-fsck: (23 commits)
coccinelle: update commit.cocci
commit-graph: update design document
gc: automatically write commit-graph files
commit-graph: add '--reachable' option
commit-graph: use string-list API for input
fsck: verify commit-graph
commit-graph: verify contents match checksum
commit-graph: test for corrupted octopus edge
commit-graph: verify commit date
commit-graph: verify generation number
commit-graph: verify parent list
commit-graph: verify root tree OIDs
commit-graph: verify objects exist
commit-graph: verify corrupt OID fanout and lookup
commit-graph: verify required chunks are present
commit-graph: verify catches corrupt signature
commit-graph: add 'verify' subcommand
commit-graph: load a root tree from specific graph
commit: force commit to parse from object database
commit-graph: parse commit from chosen graph
...
Conversion from uchar[40] to struct object_id continues.
* bc/object-id:
pretty: switch hard-coded constants to the_hash_algo
sha1-file: convert constants to uses of the_hash_algo
log-tree: switch GIT_SHA1_HEXSZ to the_hash_algo->hexsz
diff: switch GIT_SHA1_HEXSZ to use the_hash_algo
builtin/merge-recursive: make hash independent
builtin/merge: switch to use the_hash_algo
builtin/fmt-merge-msg: make hash independent
builtin/update-index: simplify parsing of cacheinfo
builtin/update-index: convert to using the_hash_algo
refs/files-backend: use the_hash_algo for writing refs
sha1-name: use the_hash_algo when parsing object names
strbuf: allocate space with GIT_MAX_HEXSZ
commit: express tree entry constants in terms of the_hash_algo
hex: switch to using the_hash_algo
tree-walk: replace hard-coded constants with the_hash_algo
cache: update object ID functions for the_hash_algo
The conversion to pass "the_repository" and then "a_repository"
throughout the object access API continues.
* sb/object-store-grafts:
commit: allow lookup_commit_graft to handle arbitrary repositories
commit: allow prepare_commit_graft to handle arbitrary repositories
shallow: migrate shallow information into the object parser
path.c: migrate global git_path_* to take a repository argument
cache: convert get_graft_file to handle arbitrary repositories
commit: convert read_graft_file to handle arbitrary repositories
commit: convert register_commit_graft to handle arbitrary repositories
commit: convert commit_graft_pos() to handle arbitrary repositories
shallow: add repository argument to is_repository_shallow
shallow: add repository argument to check_shallow_file_for_update
shallow: add repository argument to register_shallow
shallow: add repository argument to set_alternate_shallow_file
commit: add repository argument to lookup_commit_graft
commit: add repository argument to prepare_commit_graft
commit: add repository argument to read_graft_file
commit: add repository argument to register_commit_graft
commit: add repository argument to commit_graft_pos
object: move grafts to object parser
object-store: move object access functions to object-store.h
Add a struct repository argument to the functions in commit-graph.h that
read the commit graph. (This commit does not affect functions that write
commit graphs.)
Because the commit graph functions can now read the commit graph of any
repository, the global variable core_commit_graph has been removed.
Instead, the config option core.commitGraph is now read on the first
time in a repository that a commit is attempted to be parsed using its
commit graph.
This commit includes a test that exercises the functionality on an
arbitrary repository that is not the_repository.
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Specify these constants in terms of the size of the hash algorithm
currently in use.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add a repository argument to allow the callers of deref_tag
to be more specific about which repository to act on. This is a small
mechanical change; it doesn't change the implementation to handle
repositories other than the_repository yet.
As with the previous commits, use a macro to catch callers passing a
repository other than the_repository at compile time.
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add a repository argument to allow callers of get_cached_commit_buffer to
be more specific about which repository to handle. This is a small
mechanical change; it doesn't change the implementation to handle
repositories other than the_repository yet.
As with the previous commits, use a macro to catch callers passing a
repository other than the_repository at compile time.
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add a repository argument to allow callers of set_commit_buffer to
be more specific about which repository to handle. This is a small
mechanical change; it doesn't change the implementation to handle
repositories other than the_repository yet.
As with the previous commits, use a macro to catch callers passing a
repository other than the_repository at compile time.
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add a repository argument to allow the callers of parse_commit_buffer
to be more specific about which repository to act on. This is a small
mechanical change; it doesn't change the implementation to handle
repositories other than the_repository yet.
As with the previous commits, use a macro to catch callers passing a
repository other than the_repository at compile time.
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add a repository argument to allow callers of lookup_commit to be more
specific about which repository to handle. This is a small mechanical
change; it doesn't change the implementation to handle repositories
other than the_repository yet.
As with the previous commits, use a macro to catch callers passing a
repository other than the_repository at compile time.
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add a repository argument to allow callers of lookup_commit_reference
to be more specific about which repository to handle. This is a small
mechanical change; it doesn't change the implementation to handle
repositories other than the_repository yet.
As with the previous commits, use a macro to catch callers passing a
repository other than the_repository at compile time.
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add a repository argument to allow callers of
lookup_commit_reference_gently to be more specific about which
repository to handle. This is a small mechanical change; it doesn't
change the implementation to handle repositories other than
the_repository yet.
As with the previous commits, use a macro to catch callers passing a
repository other than the_repository at compile time.
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add a repository argument to allow the callers of lookup_tree
to be more specific about which repository to act on. This is a small
mechanical change; it doesn't change the implementation to handle
repositories other than the_repository yet.
As with the previous commits, use a macro to catch callers passing a
repository other than the_repository at compile time.
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add a repository argument to allow callers of lookup_object to be more
specific about which repository to handle. This is a small mechanical
change; it doesn't change the implementation to handle repositories
other than the_repository yet.
As with the previous commits, use a macro to catch callers passing a
repository other than the_repository at compile time.
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add a repository argument to allow the callers of parse_object
to be more specific about which repository to act on. This is a small
mechanical change; it doesn't change the implementation to handle
repositories other than the_repository yet.
As with the previous commits, use a macro to catch callers passing a
repository other than the_repository at compile time.
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In anticipation of verifying commit-graph file contents against the
object database, create parse_commit_internal() to allow side-stepping
the commit-graph file and parse directly from the object database.
Due to the use of generation numbers, this method should not be called
unless the intention is explicit in avoiding commits from the
commit-graph file.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The conversion to pass "the_repository" and then "a_repository"
throughout the object access API continues.
* sb/object-store-alloc:
alloc: allow arbitrary repositories for alloc functions
object: allow create_object to handle arbitrary repositories
object: allow grow_object_hash to handle arbitrary repositories
alloc: add repository argument to alloc_commit_index
alloc: add repository argument to alloc_report
alloc: add repository argument to alloc_object_node
alloc: add repository argument to alloc_tag_node
alloc: add repository argument to alloc_commit_node
alloc: add repository argument to alloc_tree_node
alloc: add repository argument to alloc_blob_node
object: add repository argument to grow_object_hash
object: add repository argument to create_object
repository: introduce parsed objects field
Update to ds/generation-numbers topic.
* ds/commit-graph-lockfile-fix:
commit-graph: fix UX issue when .lock file exists
commit-graph.txt: update design document
merge: check config before loading commits
commit: use generation number in remove_redundant()
commit: add short-circuit to paint_down_to_common()
commit: use generation numbers for in_merge_bases()
ref-filter: use generation number for --contains
commit-graph: always load commit-graph information
commit: use generations in paint_down_to_common()
commit-graph: compute generation numbers
commit: add generation number to struct commit
ref-filter: fix outdated comment on in_commit_list
The in-core "commit" object had an all-purpose "void *util" field,
which was tricky to use especially in library-ish part of the
code. All of the existing uses of the field has been migrated to a
more dedicated "commit-slab" mechanism and the field is eliminated.
* nd/commit-util-to-slab:
commit.h: delete 'util' field in struct commit
merge: use commit-slab in merge remote desc instead of commit->util
log: use commit-slab in prepare_bases() instead of commit->util
show-branch: note about its object flags usage
show-branch: use commit-slab for commit-name instead of commit->util
name-rev: use commit-slab for rev-name instead of commit->util
bisect.c: use commit-slab for commit weight instead of commit->util
revision.c: use commit-slab for show_source
sequencer.c: use commit-slab to associate todo items to commits
sequencer.c: use commit-slab to mark seen commits
shallow.c: use commit-slab for commit depth instead of commit->util
describe: use commit-slab for commit names instead of commit->util
blame: use commit-slab for blame suspects instead of commit->util
commit-slab: support shared commit-slab
commit-slab.h: code split
"index-pack --strict" has been taught to make sure that it runs the
final object integrity checks after making the freshly indexed
packfile available to itself.
* jk/index-pack-maint:
index-pack: correct install_packed_git() args
index-pack: handle --strict checks of non-repo packs
prepare_commit_graft: treat non-repository as a noop
The parse_commit_buffer() function consults lookup_commit_graft()
to see if we need to rewrite parents. The latter will look
at $GIT_DIR/info/grafts. If you're outside of a repository,
then this will trigger a BUG() as of b1ef400eec (setup_git_env:
avoid blind fall-back to ".git", 2016-10-20).
It's probably uncommon to actually parse a commit outside of
a repository, but you can see it in action with:
cd /not/a/git/repo
git index-pack --strict /some/file.pack
This works fine without --strict, but the fsck checks will
try to parse any commits, triggering the BUG(). We can fix
that by teaching the graft code to behave as if there are no
grafts when we aren't in a repository.
Arguably index-pack (and fsck) are wrong to consider grafts
at all. So another solution is to disable grafts entirely
for those commands. But given that the graft feature is
deprecated anyway, it's not worth even thinking through the
ramifications that might have.
There is one other corner case I considered here. What
should:
cd /not/a/git/repo
export GIT_GRAFT_FILE=/file/with/grafts
git index-pack --strict /some/file.pack
do? We don't have a repository, but the user has pointed us
directly at a graft file, which we could respect. I believe
this case did work that way prior to b1ef400eec. However,
fixing it now would be pretty invasive. Back then we would
just call into setup_git_env() even without a repository.
But these days it actually takes a git_dir argument. So
there would be a fair bit of refactoring of the setup code
involved.
Given the obscurity of this case, plus the fact that grafts
are deprecated and probably shouldn't work under index-pack
anyway, it's not worth pursuing further. This patch at least
un-breaks the common case where you're _not_ using grafts,
but we BUG() anyway trying to even find that out.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Conversion from uchar[20] to struct object_id continues.
* bc/object-id: (42 commits)
merge-one-file: compute empty blob object ID
add--interactive: compute the empty tree value
Update shell scripts to compute empty tree object ID
sha1_file: only expose empty object constants through git_hash_algo
dir: use the_hash_algo for empty blob object ID
sequencer: use the_hash_algo for empty tree object ID
cache-tree: use is_empty_tree_oid
sha1_file: convert cached object code to struct object_id
builtin/reset: convert use of EMPTY_TREE_SHA1_BIN
builtin/receive-pack: convert one use of EMPTY_TREE_SHA1_HEX
wt-status: convert two uses of EMPTY_TREE_SHA1_HEX
submodule: convert several uses of EMPTY_TREE_SHA1_HEX
sequencer: convert one use of EMPTY_TREE_SHA1_HEX
merge: convert empty tree constant to the_hash_algo
builtin/merge: switch tree functions to use object_id
builtin/am: convert uses of EMPTY_TREE_SHA1_BIN to the_hash_algo
sha1-file: add functions for hex empty tree and blob OIDs
builtin/receive-pack: avoid hard-coded constants for push certs
diff: specify abbreviation size in terms of the_hash_algo
upload-pack: replace use of several hard-coded constants
...
The functionality of "$GIT_DIR/info/grafts" has been superseded by
the "refs/replace/" mechanism for some time now, but the internal
code had support for it in many places, which has been cleaned up
in order to drop support of the "grafts" mechanism.
* js/deprecate-grafts:
Remove obsolete script to convert grafts to replace refs
technical/shallow: describe why shallow cannot use replace refs
technical/shallow: stop referring to grafts
filter-branch: stop suggesting to use grafts
Deprecate support for .git/info/grafts
Add a test for `git replace --convert-graft-file`
replace: introduce --convert-graft-file
replace: prepare create_graft() for converting graft files wholesale
replace: "libify" create_graft() and callees
replace: avoid using die() to indicate a bug
commit: Let the callback of for_each_mergetag return on error
argv_array: offer to split a string by whitespace
The code has been taught to use the duplicated information stored
in the commit-graph file to learn the tree object name for a commit
to avoid opening and parsing the commit object when it makes sense
to do so.
* ds/lazy-load-trees:
coccinelle: avoid wrong transformation suggestions from commit.cocci
commit-graph: lazy-load trees for commits
treewide: replace maybe_tree with accessor methods
commit: create get_commit_tree() method
treewide: rename tree to maybe_tree
The static remove_redundant() method is used to filter a list
of commits by removing those that are reachable from another
commit in the list. This is used to remove all possible merge-
bases except a maximal, mutually independent set.
To determine these commits are independent, we use a number of
paint_down_to_common() walks and use the PARENT1, PARENT2 flags
to determine reachability. Since we only care about reachability
and not the full set of merge-bases between 'one' and 'twos', we
can use the 'min_generation' parameter to short-circuit the walk.
When no commit-graph exists, there is no change in behavior.
For a copy of the Linux repository, we measured the following
performance improvements:
git merge-base v3.3 v4.5
Before: 234 ms
After: 208 ms
Rel %: -11%
git merge-base v4.3 v4.5
Before: 102 ms
After: 83 ms
Rel %: -19%
The experiments above were chosen to demonstrate that we are
improving the filtering of the merge-base set. In the first
example, more time is spent walking the history to find the
set of merge bases before the remove_redundant() call. The
starting commits are closer together in the second example,
therefore more time is spent in remove_redundant(). The relative
change in performance differs as expected.
Reported-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When running 'git branch --contains', the in_merge_bases_many()
method calls paint_down_to_common() to discover if a specific
commit is reachable from a set of branches. Commits with lower
generation number are not needed to correctly answer the
containment query of in_merge_bases_many().
Add a new parameter, min_generation, to paint_down_to_common() that
prevents walking commits with generation number strictly less than
min_generation. If 0 is given, then there is no functional change.
For in_merge_bases_many(), we can pass commit->generation as the
cutoff, and this saves time during 'git branch --contains' queries
that would otherwise walk "around" the commit we are inspecting.
For a copy of the Linux repository, where HEAD is checked out at
v4.13~100, we get the following performance improvement for
'git branch --contains' over the previous commit:
Before: 0.21s
After: 0.13s
Rel %: -38%
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The containment algorithm for 'git branch --contains' is different
from that for 'git tag --contains' in that it uses is_descendant_of()
instead of contains_tag_algo(). The expensive portion of the branch
algorithm is computing merge bases.
When a commit-graph file exists with generation numbers computed,
we can avoid this merge-base calculation when the target commit has
a larger generation number than the initial commits.
Performance tests were run on a copy of the Linux repository where
HEAD is contained in v4.13 but no earlier tag. Also, all tags were
copied to branches and 'git branch --contains' was tested:
Before: 60.0s
After: 0.4s
Rel %: -99.3%
Reported-by: Jeff King <peff@peff.net>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Most code paths load commits using lookup_commit() and then
parse_commit(). In some cases, including some branch lookups, the commit
is parsed using parse_object_buffer() which side-steps parse_commit() in
favor of parse_commit_buffer().
With generation numbers in the commit-graph, we need to ensure that any
commit that exists in the commit-graph file has its generation number
loaded.
Create new load_commit_graph_info() method to fill in the information
for a commit that exists only in the commit-graph file. Call it from
parse_commit_buffer() after loading the other commit information from
the given buffer. Only fill this information when specified by the
'check_graph' parameter.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Define compare_commits_by_gen_then_commit_date(), which uses generation
numbers as a primary comparison and commit date to break ties (or as a
comparison when both commits do not have computed generation numbers).
Since the commit-graph file is closed under reachability, we know that
all commits in the file have generation at most GENERATION_NUMBER_MAX
which is less than GENERATION_NUMBER_INFINITY.
This change does not affect the number of commits that are walked during
the execution of paint_down_to_common(), only the order that those
commits are inspected. In the case that commit dates violate topological
order (i.e. a parent is "newer" than a child), the previous code could
walk a commit twice: if a commit is reached with the PARENT1 bit, but
later is re-visited with the PARENT2 bit, then that PARENT2 bit must be
propagated to its parents. Using generation numbers avoids this extra
effort, even if it is somewhat rare.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
It's done so that commit->util can be removed. See more explanation in
the commit that removes commit->util.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Move the global variable 'commit_graft_prepared' into the object
pool and convert the function prepare_commit_graft to work
an arbitrary repositories.
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This conversion was done without the #define trick used in the earlier
series refactoring to have better repository access, because this function
is easy to review, as all lines are converted and it has only one caller.
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
