@matheusbsbs / matheus-bagliano / commits / 55088ac8a4

describe: limit default ref iteration to tags

Without --all, git describe ignores refs outside refs/tags/. Commit 8a5a1884e9 (Avoid accessing non-tag refs in git-describe unless --all is requested, 2008-02-24) moved this check ahead of object lookup. That avoided loading objects for irrelevant refs, but the backend still has to yield every ref before get_name() can reject it. Pass refs/tags/ to the iterator so the backend can avoid visiting those refs in the first place. The new perf test creates 10,000 unrelated packed refs. It measures: git describe --exact-match HEAD The runtime drops from 0.03(0.01+0.01) to 0.02(0.00+0.00). In a repository with 120,532 refs but only 330 tags, the same command went from 171.7 ms to 9.9 ms. Signed-off-by: Tamir Duberstein <tamird@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Tamir Duberstein committed Jun 10, 2026 at 11:50 UTC 55088ac8a480d94ccf37bc53b6b2ddc7475b269b

2 files changed +15

builtin/describe.c

@@ -740,6 +740,9 @@ int cmd_describe(int argc,

740 return ret;

741 }

742

743 + if (!all)

744 + for_each_ref_opts.prefix = "refs/tags/";

745 +

746 hashmap_init(&names, commit_name_neq, NULL, 0);

747 refs_for_each_ref_ext(get_main_ref_store(the_repository),

748 get_name, NULL, &for_each_ref_opts);

t/perf/p6100-describe.sh

+12

@@ -27,4 +27,16 @@ test_perf 'describe HEAD with one tag' '

27 git describe --match=new HEAD

28 '

30 +test_expect_success 'set up many unrelated refs' '

31 + ref_count=10000 &&

32 + git tag -m tip tip HEAD &&

33 + test_seq -f "create refs/heads/describe-perf/%05d HEAD" $ref_count |

34 + git update-ref --stdin &&

35 + git pack-refs --all

36 +'

37 +

38 +test_perf 'describe exact tag with many unrelated refs' '

39 + git describe --exact-match HEAD

40 +'

41 +

42 test_done