commit: integrate commit graph with commit parsing

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>

Author: derrickstolee

alloc.c

@@ -93,6 +93,7 @@ void *alloc_commit_node(void)
 struct commit *c = alloc_node(&commit_state, sizeof(struct commit));
 c->object.type = OBJ_COMMIT;
 c->index = alloc_commit_index();
+c->graph_pos = COMMIT_NOT_FROM_GRAPH;
 return c;
 }
 

commit-graph.c

@@ -38,7 +38,6 @@
 #define GRAPH_MIN_SIZE (5 * GRAPH_CHUNKLOOKUP_WIDTH + GRAPH_FANOUT_SIZE + \
 GRAPH_OID_LEN + 8)
 
-
 char *get_commit_graph_filename(const char *obj_dir)
 {
 return xstrfmt("%s/info/commit-graph", obj_dir);
@@ -179,6 +178,145 @@ struct commit_graph *load_commit_graph_one(const char *graph_file)
 exit(1);
 }
 
+/* global storage */
+struct commit_graph *commit_graph = NULL;
+
+static void prepare_commit_graph_one(const char *obj_dir)
+{
+char *graph_name;
+
+if (commit_graph)
+return;
+
+graph_name = get_commit_graph_filename(obj_dir);
+commit_graph = load_commit_graph_one(graph_name);
+
+FREE_AND_NULL(graph_name);
+}
+
+static int prepare_commit_graph_run_once = 0;
+static void prepare_commit_graph(void)
+{
+struct alternate_object_database *alt;
+char *obj_dir;
+
+if (prepare_commit_graph_run_once)
+return;
+prepare_commit_graph_run_once = 1;
+
+obj_dir = get_object_directory();
+prepare_commit_graph_one(obj_dir);
+prepare_alt_odb();
+for (alt = alt_odb_list; !commit_graph && alt; alt = alt->next)
+prepare_commit_graph_one(alt->path);
+}
+
+static void close_commit_graph(void)
+{
+if (!commit_graph)
+return;
+
+if (commit_graph->graph_fd >= 0) {
+munmap((void *)commit_graph->data, commit_graph->data_len);
+commit_graph->data = NULL;
+close(commit_graph->graph_fd);
+}
+
+FREE_AND_NULL(commit_graph);
+}
+
+static int bsearch_graph(struct commit_graph *g, struct object_id *oid, uint32_t *pos)
+{
+return bsearch_hash(oid->hash, g->chunk_oid_fanout,
+ g->chunk_oid_lookup, g->hash_len, pos);
+}
+
+static struct commit_list **insert_parent_or_die(struct commit_graph *g,
+ uint64_t pos,
+ struct commit_list **pptr)
+{
+struct commit *c;
+struct object_id oid;
+hashcpy(oid.hash, g->chunk_oid_lookup + g->hash_len * pos);
+c = lookup_commit(&oid);
+if (!c)
+die("could not find commit %s", oid_to_hex(&oid));
+c->graph_pos = pos;
+return &commit_list_insert(c, pptr)->next;
+}
+
+static int fill_commit_in_graph(struct commit *item, struct commit_graph *g, uint32_t pos)
+{
+struct object_id oid;
+uint32_t edge_value;
+uint32_t *parent_data_ptr;
+uint64_t date_low, date_high;
+struct commit_list **pptr;
+const unsigned char *commit_data = g->chunk_commit_data + (g->hash_len + 16) * pos;
+
+item->object.parsed = 1;
+item->graph_pos = pos;
+
+hashcpy(oid.hash, commit_data);
+item->tree = lookup_tree(&oid);
+
+date_high = get_be32(commit_data + g->hash_len + 8) & 0x3;
+date_low = get_be32(commit_data + g->hash_len + 12);
+item->date = (timestamp_t)((date_high << 32) | date_low);
+
+pptr = &item->parents;
+
+edge_value = get_be32(commit_data + g->hash_len);
+if (edge_value == GRAPH_PARENT_NONE)
+return 1;
+pptr = insert_parent_or_die(g, edge_value, pptr);
+
+edge_value = get_be32(commit_data + g->hash_len + 4);
+if (edge_value == GRAPH_PARENT_NONE)
+return 1;
+if (!(edge_value & GRAPH_OCTOPUS_EDGES_NEEDED)) {
+pptr = insert_parent_or_die(g, edge_value, pptr);
+return 1;
+}
+
+parent_data_ptr = (uint32_t*)(g->chunk_large_edges +
+ 4 * (uint64_t)(edge_value & GRAPH_EDGE_LAST_MASK));
+do {
+edge_value = get_be32(parent_data_ptr);
+pptr = insert_parent_or_die(g,
+ edge_value & GRAPH_EDGE_LAST_MASK,
+ pptr);
+parent_data_ptr++;
+} while (!(edge_value & GRAPH_LAST_EDGE));
+
+return 1;
+}
+
+int parse_commit_in_graph(struct commit *item)
+{
+if (!core_commit_graph)
+return 0;
+if (item->object.parsed)
+return 1;
+
+prepare_commit_graph();
+if (commit_graph) {
+uint32_t pos;
+int found;
+if (item->graph_pos != COMMIT_NOT_FROM_GRAPH) {
+pos = item->graph_pos;
+found = 1;
+} else {
+found = bsearch_graph(commit_graph, &(item->object.oid), &pos);
+}
+
+if (found)
+return fill_commit_in_graph(item, commit_graph, pos);
+}
+
+return 0;
+}
+
 static void write_graph_chunk_fanout(struct hashfile *f,
  struct commit **commits,
  int nr_commits)
@@ -530,6 +668,7 @@ void write_commit_graph(const char *obj_dir)
 write_graph_chunk_data(f, GRAPH_OID_LEN, commits.list, commits.nr);
 write_graph_chunk_large_edges(f, commits.list, commits.nr);
 
+close_commit_graph();
 finalize_hashfile(f, NULL, CSUM_HASH_IN_STREAM | CSUM_FSYNC);
 commit_lock_file(&lk);
 

commit-graph.h

@@ -5,6 +5,18 @@
 
 char *get_commit_graph_filename(const char *obj_dir);
 
+/*
+ * Given a commit struct, try to fill the commit struct info, including:
+ * 1. tree object
+ * 2. date
+ * 3. parents.
+ *
+ * Returns 1 if and only if the commit was found in the packed graph.
+ *
+ * See parse_commit_buffer() for the fallback after this call.
+ */
+int parse_commit_in_graph(struct commit *item);
+
 struct commit_graph {
 int graph_fd;
 

commit.c

@@ -1,6 +1,7 @@
 #include "cache.h"
 #include "tag.h"
 #include "commit.h"
+#include "commit-graph.h"
 #include "pkt-line.h"
 #include "utf8.h"
 #include "diff.h"
@@ -383,6 +384,8 @@ int parse_commit_gently(struct commit *item, int quiet_on_missing)
 return -1;
 if (item->object.parsed)
 return 0;
+if (parse_commit_in_graph(item))
+return 0;
 buffer = read_sha1_file(item->object.oid.hash, &type, &size);
 if (!buffer)
 return quiet_on_missing ? -1 :

commit.h

@@ -9,6 +9,8 @@
 #include "string-list.h"
 #include "pretty.h"
 
+#define COMMIT_NOT_FROM_GRAPH 0xFFFFFFFF
+
 struct commit_list {
 struct commit *item;
 struct commit_list *next;
@@ -21,6 +23,7 @@ struct commit {
 timestamp_t date;
 struct commit_list *parents;
 struct tree *tree;
+uint32_t graph_pos;
 };
 
 extern int save_commit_buffer;

t/t5318-commit-graph.sh

@@ -7,6 +7,7 @@ test_expect_success 'setup full repo' '
 mkdir full &&
 cd "$TRASH_DIRECTORY/full" &&
 git init &&
+git config core.commitGraph true &&
 objdir=".git/objects"
 '
 
@@ -26,6 +27,29 @@ test_expect_success 'create commits and repack' '
 git repack
 '
 
+graph_git_two_modes() {
+git -c core.graph=true $1 >output
+git -c core.graph=false $1 >expect
+test_cmp output expect
+}
+
+graph_git_behavior() {
+MSG=$1
+DIR=$2
+BRANCH=$3
+COMPARE=$4
+test_expect_success "check normal git operations: $MSG" '
+cd "$TRASH_DIRECTORY/$DIR" &&
+graph_git_two_modes "log --oneline $BRANCH" &&
+graph_git_two_modes "log --topo-order $BRANCH" &&
+graph_git_two_modes "log --graph $COMPARE..$BRANCH" &&
+graph_git_two_modes "branch -vv" &&
+graph_git_two_modes "merge-base -a $BRANCH $COMPARE"
+'
+}
+
+graph_git_behavior 'no graph' full commits/3 commits/1
+
 graph_read_expect() {
 OPTIONAL=""
 NUM_CHUNKS=3
@@ -50,6 +74,8 @@ test_expect_success 'write graph' '
 graph_read_expect "3"
 '
 
+graph_git_behavior 'graph exists' full commits/3 commits/1
+
 test_expect_success 'Add more commits' '
 cd "$TRASH_DIRECTORY/full" &&
 git reset --hard commits/1 &&
@@ -86,14 +112,17 @@ test_expect_success 'Add more commits' '
 # |___/____/
 # 1
 
-
 test_expect_success 'write graph with merges' '
 cd "$TRASH_DIRECTORY/full" &&
 git commit-graph write &&
 test_path_is_file $objdir/info/commit-graph &&
 graph_read_expect "10" "large_edges"
 '
 
+graph_git_behavior 'merge 1 vs 2' full merge/1 merge/2
+graph_git_behavior 'merge 1 vs 3' full merge/1 merge/3
+graph_git_behavior 'merge 2 vs 3' full merge/2 merge/3
+
 test_expect_success 'Add one more commit' '
 cd "$TRASH_DIRECTORY/full" &&
 test_commit 8 &&
@@ -115,32 +144,48 @@ test_expect_success 'Add one more commit' '
 # |___/____/
 # 1
 
+graph_git_behavior 'mixed mode, commit 8 vs merge 1' full commits/8 merge/1
+graph_git_behavior 'mixed mode, commit 8 vs merge 2' full commits/8 merge/2
+
 test_expect_success 'write graph with new commit' '
 cd "$TRASH_DIRECTORY/full" &&
 git commit-graph write &&
 test_path_is_file $objdir/info/commit-graph &&
 graph_read_expect "11" "large_edges"
 '
 
+graph_git_behavior 'full graph, commit 8 vs merge 1' full commits/8 merge/1
+graph_git_behavior 'full graph, commit 8 vs merge 2' full commits/8 merge/2
+
 test_expect_success 'write graph with nothing new' '
 cd "$TRASH_DIRECTORY/full" &&
 git commit-graph write &&
 test_path_is_file $objdir/info/commit-graph &&
 graph_read_expect "11" "large_edges"
 '
 
+graph_git_behavior 'cleared graph, commit 8 vs merge 1' full commits/8 merge/1
+graph_git_behavior 'cleared graph, commit 8 vs merge 2' full commits/8 merge/2
+
 test_expect_success 'setup bare repo' '
 cd "$TRASH_DIRECTORY" &&
 git clone --bare --no-local full bare &&
 cd bare &&
+git config core.commitGraph true &&
 baredir="./objects"
 '
 
+graph_git_behavior 'bare repo, commit 8 vs merge 1' bare commits/8 merge/1
+graph_git_behavior 'bare repo, commit 8 vs merge 2' bare commits/8 merge/2
+
 test_expect_success 'write graph in bare repo' '
 cd "$TRASH_DIRECTORY/bare" &&
 git commit-graph write &&
 test_path_is_file $baredir/info/commit-graph &&
 graph_read_expect "11" "large_edges"
 '
 
+graph_git_behavior 'bare repo with graph, commit 8 vs merge 1' bare commits/8 merge/1
+graph_git_behavior 'bare repo with graph, commit 8 vs merge 2' bare commits/8 merge/2
+
 test_done