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pack-objects: support reachability bitmaps with --path-walk
When 'pack-objects' is invoked with '--path-walk', it prevents us from using reachability bitmaps. This behavior dates back to70664d2865(pack-objects: add --path-walk option, 2025-05-16), which included a comment in the relevant portion of the command-line arguments handling that read as follows: /* * We must disable the bitmaps because we are removing * the --objects / --objects-edge[-aggressive] options. */ Infb2c309b7d(pack-objects: pass --objects with --path-walk, 2026-05-02), path-walk learned to pass '--objects' again, but still kept bitmap traversal disabled. That leaves two useful cases unsupported: * A path-walk repack that writes bitmaps does not give the bitmap selector any commits, because path-walk reveals commits through `add_objects_by_path()` rather than through `show_commit()`, where `index_commit_for_bitmap()` is normally called. * An invocation like "git pack-objects --use-bitmap-index --path-walk" never tries an existing bitmap, even when one is available and could answer the request. Fortunately for us, neither restriction is required. * On the writing side: teach the path-walk object callback to call `index_commit_for_bitmap()` for commits that it adds to the pack. That gives the bitmap selector the commit candidates it would have seen from the regular traversal. * For bitmap reading, keep passing '--objects' to the internal rev_list machinery, but stop clearing `use_bitmap_index`. If an existing bitmap can answer the request, use it; otherwise fall back to path-walk's own enumeration. As a result, we can see significantly reduced pack sizes from p5311 before this commit: Test HEAD^ HEAD ---------------------------------------------------------------------------------- 5311.38: server (1 days, --path-walk) 2.56(2.52+0.03) 0.01(0.01+0.00) -99.6% 5311.39: size (1 days, --path-walk) 123.9K 123.9K +0.0% 5311.40: client (1 days, --path-walk) 0.00(0.01+0.00) 0.00(0.00+0.00) = 5311.42: server (2 days, --path-walk) 2.57(2.52+0.05) 0.01(0.01+0.00) -99.6% 5311.43: size (2 days, --path-walk) 123.9K 123.9K +0.0% 5311.44: client (2 days, --path-walk) 0.00(0.00+0.00) 0.00(0.00+0.00) = 5311.46: server (4 days, --path-walk) 2.58(2.51+0.07) 0.01(0.01+0.00) -99.6% 5311.47: size (4 days, --path-walk) 123.9K 123.9K +0.0% 5311.48: client (4 days, --path-walk) 0.00(0.00+0.00) 0.00(0.00+0.00) = 5311.50: server (8 days, --path-walk) 2.58(2.53+0.04) 0.02(0.02+0.00) -99.2% 5311.51: size (8 days, --path-walk) 152.4K 152.4K +0.0% 5311.52: client (8 days, --path-walk) 0.00(0.01+0.00) 0.00(0.01+0.00) = 5311.54: server (16 days, --path-walk) 2.58(2.52+0.05) 0.03(0.02+0.00) -98.8% 5311.55: size (16 days, --path-walk) 205.3K 205.3K +0.0% 5311.56: client (16 days, --path-walk) 0.01(0.01+0.00) 0.01(0.01+0.00) +0.0% 5311.58: server (32 days, --path-walk) 2.59(2.53+0.06) 0.03(0.03+0.00) -98.8% 5311.59: size (32 days, --path-walk) 209.3K 209.3K +0.0% 5311.60: client (32 days, --path-walk) 0.01(0.02+0.00) 0.01(0.02+0.00) +0.0% 5311.62: server (64 days, --path-walk) 2.70(2.76+0.06) 0.16(0.24+0.04) -94.1% 5311.63: size (64 days, --path-walk) 4.1M 4.1M +0.0% 5311.64: client (64 days, --path-walk) 0.44(0.50+0.02) 0.44(0.51+0.02) +0.0% 5311.66: server (128 days, --path-walk) 2.88(3.20+0.05) 0.34(0.65+0.05) -88.2% 5311.67: size (128 days, --path-walk) 9.0M 9.0M -0.0% 5311.68: client (128 days, --path-walk) 0.93(1.22+0.07) 0.93(1.20+0.08) +0.0% We get the same size of output pack, but this commit allows us to do so in a significantly shorter amount of time. Intuitively, we're generating the same pack (hence the unchanged 'test_size' output from run to run), but varying how we get there. Before this commit, pack-objects prefers '--path-walk' to '--use-bitmap-index', so we generate the output pack by performing a normal '--path-walk' traversal. With this commit, we are operating over a *repacked* state (that itself was done with a '--path-walk' traversal), but are able to perform pack-reuse on that repacked state via bitmaps. There is one wrinkle when it comes to '--boundary', which we must not pass into the bitmap walk in the presence of both '--path-walk' and '--use-bitmap-index'. Path-walk needs boundary commits when it performs its own traversal, in order to discover bases for thin packs, but the bitmap traversal does not expect this. Work around this by setting `revs->boundary` as late as possible within the '--path-walk' traversal, after any bitmap attempt has either succeeded or declined to answer the request. Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Taylor Blau
committed by
Junio C Hamano
Junio C Hamano
parent
7aebfd0e08
commit
ea78edbebe
@@ -402,8 +402,10 @@ will be automatically changed to version `1`.
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of filenames that cause collisions in Git's default name-hash
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algorithm.
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+
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Incompatible with `--delta-islands`. The `--use-bitmap-index` option is
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ignored in the presence of `--path-walk`. The `--path-walk` option
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Incompatible with `--delta-islands`. When `--use-bitmap-index` is
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specified with `--path-walk`, a successful bitmap traversal is used for
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object enumeration, with path-walk remaining as the fallback traversal
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when the bitmap cannot satisfy the request. The `--path-walk` option
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supports the `--filter=<spec>` forms `blob:none`, `blob:limit=<n>`,
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`tree:0`, `object:type=<type>`, and `sparse:<oid>`. These supported filter
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types can be combined with the `combine:<spec>+<spec>` form.
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@@ -4742,6 +4742,15 @@ static int add_objects_by_path(const char *path,
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continue;
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add_object_entry(oid, type, path, exclude);
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if (type == OBJ_COMMIT && write_bitmap_index) {
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struct commit *commit;
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commit = lookup_commit(the_repository, oid);
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if (!commit)
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die(_("could not find commit %s"), oid_to_hex(oid));
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index_commit_for_bitmap(commit);
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}
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}
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oe_end = to_pack.nr_objects;
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@@ -4774,6 +4783,13 @@ static int get_object_list_path_walk(struct rev_info *revs)
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info.path_fn = add_objects_by_path;
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info.path_fn_data = &processed;
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/*
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* Path-walk needs boundary commits to discover thin-pack bases, but
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* bitmap traversal does not understand the boundary state. Set it
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* here so any prior bitmap attempt sees the usual non-boundary walk.
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*/
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revs->boundary = 1;
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/*
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* Allow the --[no-]sparse option to be interesting here, if only
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* for testing purposes. Paths with no interesting objects will not
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@@ -5205,9 +5221,7 @@ int cmd_pack_objects(int argc,
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}
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}
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if (path_walk) {
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strvec_push(&rp, "--boundary");
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strvec_push(&rp, "--objects");
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use_bitmap_index = 0;
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} else if (thin) {
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use_internal_rev_list = 1;
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strvec_push(&rp, shallow
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@@ -4,15 +4,18 @@ test_description='performance of fetches from bitmapped packs'
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. ./perf-lib.sh
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test_fetch_bitmaps () {
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argv=$1
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export argv
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test_expect_success 'setup test directory' '
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rm -fr * .git
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'
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test_perf_default_repo
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test_expect_success 'create bitmapped server repo' '
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test_expect_success "create bitmapped server repo ${argv:+($argv)}" '
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git config pack.writebitmaps true &&
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git repack -ad
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git repack -ad $argv
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'
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# simulate a fetch from a repository that last fetched N days ago, for
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@@ -20,7 +23,7 @@ test_fetch_bitmaps () {
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# and assume the first entry in the chain that is N days older than the current
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# HEAD is where the HEAD would have been then.
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for days in 1 2 4 8 16 32 64 128; do
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title=$(printf '%10s' "($days days)")
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title=$(printf '%10s' "($days days${argv:+, $argv})")
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test_expect_success "setup revs from $days days ago" '
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now=$(git log -1 --format=%ct HEAD) &&
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then=$(($now - ($days * 86400))) &&
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@@ -47,6 +50,9 @@ test_fetch_bitmaps () {
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done
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}
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test_fetch_bitmaps
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for argv in '' --path-walk
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do
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test_fetch_bitmaps $argv || return 1
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done
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test_done
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@@ -577,6 +577,42 @@ test_bitmap_cases
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sane_unset GIT_TEST_PACK_USE_BITMAP_BOUNDARY_TRAVERSAL
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test_expect_success 'path-walk repack can write and use bitmap indexes' '
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test_when_finished "rm -rf path-walk-bitmap" &&
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git init path-walk-bitmap &&
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(
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cd path-walk-bitmap &&
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test_commit first &&
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test_commit second &&
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test_commit third &&
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git repack -a -d -b --path-walk &&
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git rev-list --test-bitmap --use-bitmap-index HEAD &&
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git rev-parse HEAD >in &&
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git rev-list --objects --no-object-names HEAD >expect.raw &&
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sort expect.raw >expect &&
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for reuse in true false
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do
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: >trace.txt &&
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GIT_TRACE2_EVENT="$(pwd)/trace.txt" \
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git -c pack.allowPackReuse=$reuse pack-objects \
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--stdout --revs --path-walk --use-bitmap-index \
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<in >out.pack &&
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grep "\"category\":\"bitmap\",\"key\":\"bitmap/hits\"" trace.txt &&
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git index-pack out.pack &&
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list_packed_objects out.idx >actual.raw &&
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sort actual.raw >actual &&
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test_cmp expect actual || return 1
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done
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)
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'
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test_expect_success 'incremental repack fails when bitmaps are requested' '
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test_commit more-1 &&
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test_must_fail git repack -d 2>err &&
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