From: Derrick Stolee <dstolee@xxxxxxxxxxxxx>
When computing a changed-path Bloom filter, we need to take the
files that changed from the diff computation and extract the parent
directories. That way, a directory pathspec such as "Documentation"
could match commits that change "Documentation/git.txt".
However, the current code does a poor job of this process. The paths
are added to a hashmap, but we do not check if an entry already
exists with that path. This can create many duplicate entries and
cause the filter to have a much larger length than it should. This
means that the filter is more sparse than intended, which helps the
false positive rate, but wastes a lot of space.
Properly use hashmap_get() before hashmap_add(). Also be sure to
include a comparison function so these can be matched correctly.
This has an effect on a test in t0095-bloom.sh. This makes sense,
there are ten changes inside "smallDir" so the total number of
paths in the filter should be 11. This would result in 11 * 10 bits
required, and with 8 bits per byte, this results in 14 bytes.
Signed-off-by: Derrick Stolee <dstolee@xxxxxxxxxxxxx>
---
bloom.c | 35 ++++++++++++++++++++++++++---------
t/t0095-bloom.sh | 4 ++--
2 files changed, 28 insertions(+), 11 deletions(-)
diff --git a/bloom.c b/bloom.c
index 2e3e0f5037b..eb08571c628 100644
--- a/bloom.c
+++ b/bloom.c
@@ -158,6 +158,19 @@ void init_bloom_filters(void)
init_bloom_filter_slab(&bloom_filters);
}
+static int pathmap_cmp(const void *hashmap_cmp_fn_data,
+ const struct hashmap_entry *eptr,
+ const struct hashmap_entry *entry_or_key,
+ const void *keydata)
+{
+ const struct pathmap_hash_entry *e1, *e2;
+
+ e1 = container_of(eptr, const struct pathmap_hash_entry, entry);
+ e2 = container_of(entry_or_key, const struct pathmap_hash_entry, entry);
+
+ return strcmp(e1->path, e2->path);
+}
+
struct bloom_filter *get_bloom_filter(struct repository *r,
struct commit *c,
int compute_if_not_present)
@@ -203,25 +216,29 @@ struct bloom_filter *get_bloom_filter(struct repository *r,
struct hashmap pathmap;
struct pathmap_hash_entry *e;
struct hashmap_iter iter;
- hashmap_init(&pathmap, NULL, NULL, 0);
+ hashmap_init(&pathmap, pathmap_cmp, NULL, 0);
for (i = 0; i < diff_queued_diff.nr; i++) {
const char *path = diff_queued_diff.queue[i]->two->path;
/*
- * Add each leading directory of the changed file, i.e. for
- * 'dir/subdir/file' add 'dir' and 'dir/subdir' as well, so
- * the Bloom filter could be used to speed up commands like
- * 'git log dir/subdir', too.
- *
- * Note that directories are added without the trailing '/'.
- */
+ * Add each leading directory of the changed file, i.e. for
+ * 'dir/subdir/file' add 'dir' and 'dir/subdir' as well, so
+ * the Bloom filter could be used to speed up commands like
+ * 'git log dir/subdir', too.
+ *
+ * Note that directories are added without the trailing '/'.
+ */
do {
char *last_slash = strrchr(path, '/');
FLEX_ALLOC_STR(e, path, path);
hashmap_entry_init(&e->entry, strhash(path));
- hashmap_add(&pathmap, &e->entry);
+
+ if (!hashmap_get(&pathmap, &e->entry, NULL))
+ hashmap_add(&pathmap, &e->entry);
+ else
+ free(e);
if (!last_slash)
last_slash = (char*)path;
diff --git a/t/t0095-bloom.sh b/t/t0095-bloom.sh
index 8f9eef116dc..6defeb544f1 100755
--- a/t/t0095-bloom.sh
+++ b/t/t0095-bloom.sh
@@ -89,8 +89,8 @@ test_expect_success 'get bloom filter for commit with 10 changes' '
git add smallDir &&
git commit -m "commit with 10 changes" &&
cat >expect <<-\EOF &&
- Filter_Length:25
- Filter_Data:82|a0|65|47|0c|92|90|c0|a1|40|02|a0|e2|40|e0|04|0a|9a|66|cf|80|19|85|42|23|
+ Filter_Length:14
+ Filter_Data:02|b3|c4|a0|34|e7|fe|eb|cb|47|fe|a0|e8|72|
EOF
test-tool bloom get_filter_for_commit "$(git rev-parse HEAD)" >actual &&
test_cmp expect actual
--
gitgitgadget
