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2018-06-25Merge branch 'ds/commit-graph-lockfile-fix'Libravatar Junio C Hamano1-32/+81
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commit-graph: compute generation numbers commit: add generation number to struct commit ref-filter: fix outdated comment on in_commit_list
2018-05-23Merge branch 'sb/oid-object-info'Libravatar Junio C Hamano1-1/+1
The codepath around object-info API has been taught to take the repository object (which in turn tells the API which object store the objects are to be located). * sb/oid-object-info: cache.h: allow oid_object_info to handle arbitrary repositories packfile: add repository argument to cache_or_unpack_entry packfile: add repository argument to unpack_entry packfile: add repository argument to read_object packfile: add repository argument to packed_object_info packfile: add repository argument to packed_to_object_type packfile: add repository argument to retry_bad_packed_offset cache.h: add repository argument to oid_object_info cache.h: add repository argument to oid_object_info_extended
2018-05-23Merge branch 'ds/lazy-load-trees'Libravatar Junio C Hamano1-4/+24
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
2018-05-22commit-graph: fix UX issue when .lock file existsLibravatar Derrick Stolee1-17/+5
We use the lockfile API to avoid multiple Git processes from writing to the commit-graph file in the .git/objects/info directory. In some cases, this directory may not exist, so we check for its existence. The existing code does the following when acquiring the lock: 1. Try to acquire the lock. 2. If it fails, try to create the .git/object/info directory. 3. Try to acquire the lock, failing if necessary. The problem is that if the lockfile exists, then the mkdir fails, giving an error that doesn't help the user: "fatal: cannot mkdir .git/objects/info: File exists" While technically this honors the lockfile, it does not help the user. Instead, do the following: 1. Check for existence of .git/objects/info; create if necessary. 2. Try to acquire the lock, failing if necessary. The new output looks like: fatal: Unable to create '<dir>/.git/objects/info/commit-graph.lock': File exists. Another git process seems to be running in this repository, e.g. an editor opened by 'git commit'. Please make sure all processes are terminated then try again. If it still fails, a git process may have crashed in this repository earlier: remove the file manually to continue. Helped-by: Jeff King <peff@peff.net> Signed-off-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-05-22commit-graph: always load commit-graph informationLibravatar Derrick Stolee1-15/+31
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>
2018-05-22commit-graph: compute generation numbersLibravatar Derrick Stolee1-0/+43
While preparing commits to be written into a commit-graph file, compute the generation numbers using a depth-first strategy. The only commits that are walked in this depth-first search are those without a precomputed generation number. Thus, computation time will be relative to the number of new commits to the commit-graph file. If a computed generation number would exceed GENERATION_NUMBER_MAX, then use GENERATION_NUMBER_MAX instead. Signed-off-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-05-22commit: add generation number to struct commitLibravatar Derrick Stolee1-0/+2
The generation number of a commit is defined recursively as follows: * If a commit A has no parents, then the generation number of A is one. * If a commit A has parents, then the generation number of A is one more than the maximum generation number among the parents of A. Add a uint32_t generation field to struct commit so we can pass this information to revision walks. We use three special values to signal the generation number is invalid: GENERATION_NUMBER_INFINITY 0xFFFFFFFF GENERATION_NUMBER_MAX 0x3FFFFFFF GENERATION_NUMBER_ZERO 0 The first (_INFINITY) means the generation number has not been loaded or computed. The second (_MAX) means the generation number is too large to store in the commit-graph file. The third (_ZERO) means the generation number was loaded from a commit graph file that was written by a version of git that did not support generation numbers. Signed-off-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-05-08Merge branch 'ds/commit-graph'Libravatar Junio C Hamano1-0/+741
Precompute and store information necessary for ancestry traversal in a separate file to optimize graph walking. * ds/commit-graph: commit-graph: implement "--append" option commit-graph: build graph from starting commits commit-graph: read only from specific pack-indexes commit: integrate commit graph with commit parsing commit-graph: close under reachability commit-graph: add core.commitGraph setting commit-graph: implement git commit-graph read commit-graph: implement git-commit-graph write commit-graph: implement write_commit_graph() commit-graph: create git-commit-graph builtin graph: add commit graph design document commit-graph: add format document csum-file: refactor finalize_hashfile() method csum-file: rename hashclose() to finalize_hashfile()
2018-04-11commit-graph: lazy-load trees for commitsLibravatar Derrick Stolee1-3/+23
The commit-graph file provides quick access to commit data, including the OID of the root tree for each commit in the graph. When performing a deep commit-graph walk, we may not need to load most of the trees for these commits. Delay loading the tree object for a commit loaded from the graph until requested via get_commit_tree(). Do not lazy-load trees for commits not in the graph, since that requires duplicate parsing and the relative peformance improvement when trees are not needed is small. On the Linux repository, performance tests were run for the following command: git log --graph --oneline -1000 Before: 0.92s After: 0.66s Rel %: -28.3% Adding '-- kernel/' to the command requires loading the root tree for every commit that is walked. There was no measureable performance change as a result of this patch. Signed-off-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-04-11treewide: replace maybe_tree with accessor methodsLibravatar Derrick Stolee1-1/+1
In anticipation of making trees load lazily, create a Coccinelle script (contrib/coccinelle/commit.cocci) to ensure that all references to the 'maybe_tree' member of struct commit are either mutations or accesses through get_commit_tree() or get_commit_tree_oid(). Apply the Coccinelle script to create the rest of the patch. Signed-off-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-04-11treewide: rename tree to maybe_treeLibravatar Derrick Stolee1-2/+2
Using the commit-graph file to walk commit history removes the large cost of parsing commits during the walk. This exposes a performance issue: lookup_tree() takes a large portion of the computation time, even when Git never uses those trees. In anticipation of lazy-loading these trees, rename the 'tree' member of struct commit to 'maybe_tree'. This serves two purposes: it hints at the future role of possibly being NULL even if the commit has a valid tree, and it allows for unambiguous transformation from simple member access (i.e. commit->maybe_tree) to method access. Signed-off-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-04-11commit-graph: implement "--append" optionLibravatar Derrick Stolee1-1/+16
Teach git-commit-graph to add all commits from the existing commit-graph file to the file about to be written. This should be used when adding new commits without performing garbage collection. Signed-off-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-04-11commit-graph: build graph from starting commitsLibravatar Derrick Stolee1-2/+25
Teach git-commit-graph to read commits from stdin when the --stdin-commits flag is specified. Commits reachable from these commits are added to the graph. This is a much faster way to construct the graph than inspecting all packed objects, but is restricted to known tips. For the Linux repository, 700,000+ commits were added to the graph file starting from 'master' in 7-9 seconds, depending on the number of packfiles in the repo (1, 24, or 120). Signed-off-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-04-11commit-graph: read only from specific pack-indexesLibravatar Derrick Stolee1-2/+24
Teach git-commit-graph to inspect the objects only in a certain list of pack-indexes within the given pack directory. This allows updating the commit graph iteratively. Signed-off-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-04-11commit: integrate commit graph with commit parsingLibravatar Derrick Stolee1-1/+140
Teach Git to inspect a commit graph file to supply the contents of a struct commit when calling parse_commit_gently(). This implementation satisfies all post-conditions on the struct commit, including loading parents, the root tree, and the commit date. If core.commitGraph is false, then do not check graph files. In test script t5318-commit-graph.sh, add output-matching conditions on read-only graph operations. By loading commits from the graph instead of parsing commit buffers, we save a lot of time on long commit walks. Here are some performance results for a copy of the Linux repository where 'master' has 678,653 reachable commits and is behind 'origin/master' by 59,929 commits. | Command | Before | After | Rel % | |----------------------------------|--------|--------|-------| | log --oneline --topo-order -1000 | 8.31s | 0.94s | -88% | | branch -vv | 1.02s | 0.14s | -86% | | rev-list --all | 5.89s | 1.07s | -81% | | rev-list --all --objects | 66.15s | 58.45s | -11% | Signed-off-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-04-11commit-graph: close under reachabilityLibravatar Derrick Stolee1-0/+45
Teach write_commit_graph() to walk all parents from the commits discovered in packfiles. This prevents gaps given by loose objects or previously-missed packfiles. Also automatically add commits from the existing graph file, if it exists. Signed-off-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-04-11commit-graph: implement git commit-graph readLibravatar Derrick Stolee1-1/+136
Teach git-commit-graph to read commit graph files and summarize their contents. Use the read subcommand to verify the contents of a commit graph file in the tests. Signed-off-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-04-02commit-graph: implement write_commit_graph()Libravatar Derrick Stolee1-0/+359
Teach Git to write a commit graph file by checking all packed objects to see if they are commits, then store the file in the given object directory. Helped-by: Jeff King <peff@peff.net> Signed-off-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>