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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>
71 lines
1.8 KiB
C
71 lines
1.8 KiB
C
#ifndef COMMIT_GRAPH_H
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#define COMMIT_GRAPH_H
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#include "git-compat-util.h"
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#include "repository.h"
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#include "string-list.h"
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struct commit;
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char *get_commit_graph_filename(const char *obj_dir);
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/*
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* Given a commit struct, try to fill the commit struct info, including:
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* 1. tree object
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* 2. date
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* 3. parents.
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*
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* Returns 1 if and only if the commit was found in the packed graph.
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*
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* See parse_commit_buffer() for the fallback after this call.
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*/
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int parse_commit_in_graph(struct repository *r, struct commit *item);
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/*
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* It is possible that we loaded commit contents from the commit buffer,
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* but we also want to ensure the commit-graph content is correctly
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* checked and filled. Fill the graph_pos and generation members of
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* the given commit.
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*/
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void load_commit_graph_info(struct repository *r, struct commit *item);
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struct tree *get_commit_tree_in_graph(struct repository *r,
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const struct commit *c);
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struct commit_graph {
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int graph_fd;
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const unsigned char *data;
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size_t data_len;
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unsigned char hash_len;
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unsigned char num_chunks;
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uint32_t num_commits;
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struct object_id oid;
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const uint32_t *chunk_oid_fanout;
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const unsigned char *chunk_oid_lookup;
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const unsigned char *chunk_commit_data;
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const unsigned char *chunk_large_edges;
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};
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struct commit_graph *load_commit_graph_one(const char *graph_file);
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/*
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* Return 1 if and only if the repository has a commit-graph
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* file and generation numbers are computed in that file.
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*/
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int generation_numbers_enabled(struct repository *r);
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void write_commit_graph_reachable(const char *obj_dir, int append);
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void write_commit_graph(const char *obj_dir,
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struct string_list *pack_indexes,
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struct string_list *commit_hex,
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int append);
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int verify_commit_graph(struct repository *r, struct commit_graph *g);
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void free_commit_graph(struct commit_graph *);
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#endif
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