When $GIT_USE_POC_BLOOM_FILTER is set to a non-empty value, the
revision walk will use the Bloom filter to speed up a path-limited
revision walk.
Load the Bloom filter in prepare_revision_walk(); probably not the
best place for it, but it should suffice for experiementing with 'git
rev-list'.
Checking the Bloom filter is plugged into rev_compare_tree(), the
function that compares the given paths in a commit to one of its
parents. If checking the Bloom filter returns that the interesting
paths did not change, then it won't bother with the running the
expensive diff.
Add a new field to 'struct pathspec' to hold the SHA of the path, so
that hash is computed only once and then reused when checking each
commit.
---
pathspec.h | 1 +
revision.c | 97 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 98 insertions(+)
diff --git a/pathspec.h b/pathspec.h
index a6525a6551..565a26d91e 100644
--- a/pathspec.h
+++ b/pathspec.h
@@ -47,6 +47,7 @@ struct pathspec {
} match_mode;
} *attr_match;
struct attr_check *attr_check;
+ unsigned char name_hash[GIT_MAX_RAWSZ];
} *items;
};
diff --git a/revision.c b/revision.c
index c5d0cb6599..3565785ca6 100644
--- a/revision.c
+++ b/revision.c
@@ -27,6 +27,7 @@
#include "commit-reach.h"
#include "commit-graph.h"
#include "prio-queue.h"
+#include "bloom-filter.h"
volatile show_early_output_fn_t show_early_output;
@@ -463,6 +464,62 @@ static void file_change(struct diff_options *options,
options->flags.has_changes = 1;
}
+/* Another static... */
+static struct bloom_filter bf;
+
+static int check_maybe_different_in_bloom_filter(struct rev_info *revs,
+ struct commit *parent,
+ struct commit *commit)
+{
+ unsigned char p_c_hash[GIT_MAX_RAWSZ];
+ int i;
+
+ if (!bf.bits)
+ return -1;
+ /*
+ * If a commit is not in the 'commit-graph' file, then it's not in
+ * the Bloom filter either, so any query into that would report
+ * back a false negative, which is unacceptable.
+ *
+ * The writer of the Bloom filter must ensure that all commits that
+ * go into the 'commit-graph' go into the Bloom filter as well.
+ *
+ * If we won't tie the Bloom filter to the commit-graph tightly,
+ * then we'll have to come up with another means to prevent such
+ * false negatives.
+ */
+ if (!the_repository->objects->commit_graph)
+ return -1;
+ if (commit->generation == GENERATION_NUMBER_INFINITY)
+ return -1;
+
+ hashxor(parent->object.oid.hash, commit->object.oid.hash, p_c_hash);
+
+ for (i = 0; i < revs->pruning.pathspec.nr; i++) {
+ struct pathspec_item *pi = &revs->pruning.pathspec.items[i];
+ unsigned char hash[GIT_MAX_RAWSZ];
+
+ hashxor(pi->name_hash, p_c_hash, hash);
+ if (bloom_filter_check_hash(&bf, hash)) {
+ /*
+ * At least one of the interesting pathspecs differs,
+ * so we can return early and let the diff machinery
+ * make sure that they indeed differ.
+ *
+ * Note: the diff machinery will look at all the given
+ * paths; a possible future optimization might bring
+ * the Bloom filter and the diff machinery closer to
+ * each other, so the diff won't waste time looking
+ * at those paths that the Bloom filter have found
+ * unchanged.
+ */
+ return 1;
+ }
+ }
+
+ return 0;
+}
+
static int rev_compare_tree(struct rev_info *revs,
struct commit *parent, struct commit *commit)
{
@@ -492,6 +549,9 @@ static int rev_compare_tree(struct rev_info *revs,
return REV_TREE_SAME;
}
+ if (!check_maybe_different_in_bloom_filter(revs, parent, commit))
+ return REV_TREE_SAME;
+
tree_difference = REV_TREE_SAME;
revs->pruning.flags.has_changes = 0;
if (diff_tree_oid(&t1->object.oid, &t2->object.oid, "",
@@ -3106,6 +3166,40 @@ static void expand_topo_walk(struct rev_info *revs,
struct commit *commit)
}
}
+void prepare_to_use_bloom_filter(struct rev_info *revs)
+{
+ const char *env = getenv("GIT_USE_POC_BLOOM_FILTER");
+ int i;
+
+ if (!env || !*env)
+ return;
+
+ for (i = 0; i < revs->pruning.pathspec.nr; i++) {
+ struct pathspec_item *pi = &revs->pruning.pathspec.items[i];
+ const char *path = pi->match;
+ git_hash_ctx ctx;
+ size_t len = strlen(path);
+
+ /*
+ * TODO: What about wildcards? We'd probably just want to
+ * ignore the Bloom filter then.
+ */
+ the_hash_algo->init_fn(&ctx);
+ the_hash_algo->update_fn(&ctx, path,
+ path[len - 1] == '/' ? len - 1 : len);
+ the_hash_algo->final_fn(pi->name_hash, &ctx);
+ }
+
+ if (bf.bits)
+ /* Already loaded. */
+ return;
+
+ if (bloom_filter_load(&bf) < 0) {
+ warning("you wanted to use the Bloom filter, but it couldn't be
loaded");
+ return;
+ }
+}
+
int prepare_revision_walk(struct rev_info *revs)
{
int i;
@@ -3155,6 +3249,9 @@ int prepare_revision_walk(struct rev_info *revs)
simplify_merges(revs);
if (revs->children.name)
set_children(revs);
+
+ prepare_to_use_bloom_filter(revs);
+
return 0;
}
--
2.19.1.409.g0a0ee5eb6b
