Karthik Nayak <karthik.188@xxxxxxxxx> writes: > The 'git bundle create' command has non-linear performance with the > number of refs in the repository. Benchmarking the command shows that > a large portion of the time (~75%) is spent in the > `object_array_remove_duplicates()` function. > > The `object_array_remove_duplicates()` function was added in > b2a6d1c686 (bundle: allow the same ref to be given more than once, > 2009-01-17) to skip duplicate refs provided by the user from being > written to the bundle. Since this is an O(N^2) algorithm, in repos with > large number of references, this can take up a large amount of time. > > Let's instead use a 'strset' to skip duplicates inside > `write_bundle_refs()`. This improves the performance by around 6 times > when tested against in repository with 100000 refs: > > Benchmark 1: bundle (refcount = 100000, revision = master) > Time (mean ± σ): 14.653 s ± 0.203 s [User: 13.940 s, System: 0.762 s] > Range (min … max): 14.237 s … 14.920 s 10 runs > > Benchmark 2: bundle (refcount = 100000, revision = HEAD) > Time (mean ± σ): 2.394 s ± 0.023 s [User: 1.684 s, System: 0.798 s] > Range (min … max): 2.364 s … 2.425 s 10 runs > > Summary > bundle (refcount = 100000, revision = HEAD) ran > 6.12 ± 0.10 times faster than bundle (refcount = 100000, revision = master) That's a good find! > Previously, `object_array_remove_duplicates()` ensured that both the > refname and the object it pointed to were checked for duplicates. The > new approach, implemented within `write_bundle_refs()`, eliminates > duplicate refnames without comparing the objects they reference. This > works because, for bundle creation, we only need to prevent duplicate > refs from being written to the bundle header. The `revs->pending` array > can contain duplicates of multiple types. Makes sense to me. > First, references which resolve to the same refname. For e.g. "git > bundle create out.bdl master master" or "git bundle create out.bdl > refs/heads/master refs/heads/master" or "git bundle create out.bdl > master refs/heads/master". In these scenarios we want to prevent writing > "refs/heads/master" twice to the bundle header. Since both the refnames > here would point to the same object (unless there is a race), we do not > need to check equality of the object. Yeah, we can never be sure about the changes that happen while the bundle is being created. I fixed another race[1] recently which also was comparing equality of the object, that causes the ref to be omitted. We can only act by "best effort" and having the ref point to /some/ object is the best we can do. [1]: https://lore.kernel.org/git/20241211-fix-bundle-create-race-v3-1-0587f6f9db1b@xxxxxxxxx/ > Second, refnames which are duplicates but do not point to the same > object. This can happen when we use an exclusion criteria. For e.g. "git > bundle create out.bdl master master^!", Here `revs->pending` would > contain two elements, both with refname set to "master". However, each > of them would be pointing to an INTERESTING and UNINTERESTING object > respectively. Since we only write refnames with INTERESTING objects to > the bundle header, we perform our duplicate checks only on such > objects. Thanks for that context, I didn't consider that. > Signed-off-by: Karthik Nayak <karthik.188@xxxxxxxxx> > --- > bundle.c | 10 +++++++++- > object.c | 33 --------------------------------- > object.h | 6 ------ > t/t6020-bundle-misc.sh | 4 ---- > 4 files changed, 9 insertions(+), 44 deletions(-) > > diff --git a/bundle.c b/bundle.c > index d7ad690843..30cfba0be2 100644 > --- a/bundle.c > +++ b/bundle.c > @@ -384,6 +384,9 @@ static int write_bundle_refs(int bundle_fd, struct rev_info *revs) > { > int i; > int ref_count = 0; > + struct strset objects; > + > + strset_init(&objects); Any reason why you're not using the `STRMAP_INIT` macro? > > for (i = 0; i < revs->pending.nr; i++) { > struct object_array_entry *e = revs->pending.objects + i; > @@ -401,6 +404,9 @@ static int write_bundle_refs(int bundle_fd, struct rev_info *revs) > flag = 0; > display_ref = (flag & REF_ISSYMREF) ? e->name : ref; > > + if (strset_contains(&objects, display_ref)) > + goto skip_write_ref; > + > if (e->item->type == OBJ_TAG && > !is_tag_in_date_range(e->item, revs)) { > e->item->flags |= UNINTERESTING; > @@ -423,6 +429,7 @@ static int write_bundle_refs(int bundle_fd, struct rev_info *revs) > } > > ref_count++; > + strset_add(&objects, display_ref); > write_or_die(bundle_fd, oid_to_hex(&e->item->oid), the_hash_algo->hexsz); > write_or_die(bundle_fd, " ", 1); > write_or_die(bundle_fd, display_ref, strlen(display_ref)); > @@ -431,6 +438,8 @@ static int write_bundle_refs(int bundle_fd, struct rev_info *revs) > free(ref); > } > > + strset_clear(&objects); > + > /* end header */ > write_or_die(bundle_fd, "\n", 1); > return ref_count; > @@ -566,7 +575,6 @@ int create_bundle(struct repository *r, const char *path, > */ > revs.blob_objects = revs.tree_objects = 0; > traverse_commit_list(&revs, write_bundle_prerequisites, NULL, &bpi); > - object_array_remove_duplicates(&revs_copy.pending); > > /* write bundle refs */ > ref_count = write_bundle_refs(bundle_fd, &revs_copy); > diff --git a/object.c b/object.c > index 100bf9b8d1..a2c5986178 100644 > --- a/object.c > +++ b/object.c > @@ -491,39 +491,6 @@ void object_array_clear(struct object_array *array) > array->nr = array->alloc = 0; > } > > -/* > - * Return true if array already contains an entry. > - */ > -static int contains_object(struct object_array *array, > - const struct object *item, const char *name) > -{ > - unsigned nr = array->nr, i; > - struct object_array_entry *object = array->objects; > - > - for (i = 0; i < nr; i++, object++) > - if (item == object->item && !strcmp(object->name, name)) > - return 1; > - return 0; > -} > - > -void object_array_remove_duplicates(struct object_array *array) > -{ > - unsigned nr = array->nr, src; > - struct object_array_entry *objects = array->objects; > - > - array->nr = 0; > - for (src = 0; src < nr; src++) { > - if (!contains_object(array, objects[src].item, > - objects[src].name)) { > - if (src != array->nr) > - objects[array->nr] = objects[src]; > - array->nr++; > - } else { > - object_array_release_entry(&objects[src]); > - } > - } > -} > - > void clear_object_flags(unsigned flags) > { > int i; > diff --git a/object.h b/object.h > index 17f32f1103..0e12c75922 100644 > --- a/object.h > +++ b/object.h > @@ -324,12 +324,6 @@ typedef int (*object_array_each_func_t)(struct object_array_entry *, void *); > void object_array_filter(struct object_array *array, > object_array_each_func_t want, void *cb_data); > > -/* > - * Remove from array all but the first entry with a given name. > - * Warning: this function uses an O(N^2) algorithm. Funny this has been here for more than 10 years. Thanks for this cleanup. > - */ > -void object_array_remove_duplicates(struct object_array *array); > - > /* > * Remove any objects from the array, freeing all used memory; afterwards > * the array is ready to store more objects with add_object_array(). > diff --git a/t/t6020-bundle-misc.sh b/t/t6020-bundle-misc.sh > index dd09df1287..500c81b8a1 100755 > --- a/t/t6020-bundle-misc.sh > +++ b/t/t6020-bundle-misc.sh > @@ -684,7 +684,6 @@ test_expect_success 'create bundle with duplicate refnames' ' > test_cmp expect actual > ' > > -# This exhibits a bug, since the same refname is now added to the bundle twice. > test_expect_success 'create bundle with duplicate refnames and --all' ' > git bundle create out.bdl --all "main" "main" && > > @@ -701,7 +700,6 @@ test_expect_success 'create bundle with duplicate refnames and --all' ' > <TAG-2> refs/tags/v2 > <TAG-3> refs/tags/v3 > <COMMIT-P> HEAD > - <COMMIT-P> refs/heads/main > EOF > test_cmp expect actual > ' > @@ -717,7 +715,6 @@ test_expect_success 'create bundle with duplicate exlusion refnames' ' > test_cmp expect actual > ' > > -# This exhibits a bug, since the same refname is now added to the bundle twice. > test_expect_success 'create bundle with duplicate refname short-form' ' > git bundle create out.bdl "main" "main" "refs/heads/main" "refs/heads/main" && > > @@ -725,7 +722,6 @@ test_expect_success 'create bundle with duplicate refname short-form' ' > make_user_friendly_and_stable_output >actual && > cat >expect <<-\EOF && > <COMMIT-P> refs/heads/main > - <COMMIT-P> refs/heads/main > EOF > test_cmp expect actual > ' Great work on the alternative implmentation. And thanks for adding these tests and actually fixing them. I've been manually testing a few more edge cases, I couldn't find any other scenario that's not covered by the current implementation. I approve. -- Toon
