To figure out which commits we can write a bitmap for, the multi-pack index/bitmap code does a reachability traversal, marking any commit which can be found in the MIDX as eligible to receive a bitmap.
This approach will cause a problem when multi-pack bitmaps are able to be generated from `git repack`, since the reference tips can change during the repack. Even though we ignore commits that don't exist in the MIDX (when doing a scan of the ref tips), it's possible that a commit in the MIDX reaches something that isn't.
This can happen when a multi-pack index contains some pack which refers to loose objects (which by definition aren't included in the multi-pack index).
By taking a snapshot of the references before we start repacking, we can close that race window. In the above scenario (where we have a packed object pointing at a loose one), we'll either (a) take a snapshot of the references before seeing the packed one, or (b) take it after, at which point we can guarantee that the loose object will be packed and included in the MIDX.
This patch does just that. It writes a temporary "reference snapshot", which is a list of OIDs that are at the ref tips before writing a multi-pack bitmap. References that are "preferred" (i.e,. are a suffix of at least one value of the 'pack.preferBitmapTips' configuration) are marked with a special '+'.
The format is simple: one line per commit at each tip, with an optional '+' at the beginning (for preferred references, as described above).
When provided, the reference snapshot is used to drive bitmap selection instead of the MIDX code doing its own traversal. When it isn't provided, the usual traversal takes place instead.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
---
Documentation/git-multi-pack-index.txt | 15 +++++
builtin/multi-pack-index.c | 11 +++-
builtin/repack.c | 2 +-
midx.c | 60 ++++++++++++++++---
midx.h | 4 +-
t/t5326-multi-pack-bitmaps.sh | 82 ++++++++++++++++++++++++++
6 files changed, 160 insertions(+), 14 deletions(-)
Show changes to 6 files +160 −14
Documentation/git-multi-pack-index.txt, builtin/multi-pack-index.c, builtin/repack.c, midx.c, midx.h, t/t5326-multi-pack-bitmaps.sh
diff --git a/Documentation/git-multi-pack-index.txt b/Documentation/git-multi-pack-index.txt
index 009c989ef8..27f83932e4 100644
--- a/Documentation/git-multi-pack-index.txt
+++ b/Documentation/git-multi-pack-index.txt
@@ -49,6 +49,21 @@ write::
--stdin-packs::
Write a multi-pack index containing only the set of
line-delimited pack index basenames provided over stdin.
+
+ --refs-snapshot=<path>::
+ With `--bitmap`, optionally specify a file which
+ contains a "refs snapshot" taken prior to repacking.
++
+A reference snapshot is composed of line-delimited OIDs corresponding to
+the reference tips, usually taken by `git repack` prior to generating a
+new pack. A line may optionally start with a `+` character to indicate
+that the reference which corresponds to that OID is "preferred" (see
+linkgit:git-config[1]'s `pack.preferBitmapTips`.)
++
+The file given at `<path>` is expected to be readable, and can contain
+duplicates. (If a given OID is given more than once, it is marked as
+preferred if at least one instance of it begins with the special `+`
+marker).
--
verify::
diff --git a/builtin/multi-pack-index.c b/builtin/multi-pack-index.c
index 77488b6b7b..65a242f5cf 100644
--- a/builtin/multi-pack-index.c
+++ b/builtin/multi-pack-index.c
@@ -7,7 +7,8 @@
#include "object-store.h"
#define BUILTIN_MIDX_WRITE_USAGE \
- N_("git multi-pack-index [<options>] write [--preferred-pack=<pack>]")
+ N_("git multi-pack-index [<options>] write [--preferred-pack=<pack>]" \
+ "[--refs-snapshot=<path>]")
#define BUILTIN_MIDX_VERIFY_USAGE \
N_("git multi-pack-index [<options>] verify")
@@ -45,6 +46,7 @@ static char const * const builtin_multi_pack_index_usage[] = {
static struct opts_multi_pack_index {
const char *object_dir;
const char *preferred_pack;
+ const char *refs_snapshot;
unsigned long batch_size;
unsigned flags;
int stdin_packs;
@@ -82,6 +84,8 @@ static int cmd_multi_pack_index_write(int argc, const char **argv)
MIDX_WRITE_BITMAP | MIDX_WRITE_REV_INDEX),
OPT_BOOL(0, "stdin-packs", &opts.stdin_packs,
N_("write multi-pack index containing only given indexes")),
+ OPT_FILENAME(0, "refs-snapshot", &opts.refs_snapshot,
+ N_("refs snapshot for selecting bitmap commits")),
OPT_END(),
};
@@ -105,7 +109,8 @@ static int cmd_multi_pack_index_write(int argc, const char **argv)
read_packs_from_stdin(&packs);
ret = write_midx_file_only(opts.object_dir, &packs,
- opts.preferred_pack, opts.flags);
+ opts.preferred_pack,
+ opts.refs_snapshot, opts.flags);
string_list_clear(&packs, 0);
@@ -113,7 +118,7 @@ static int cmd_multi_pack_index_write(int argc, const char **argv)
}
return write_midx_file(opts.object_dir, opts.preferred_pack,
- opts.flags);
+ opts.refs_snapshot, opts.flags);
}
static int cmd_multi_pack_index_verify(int argc, const char **argv)
diff --git a/builtin/repack.c b/builtin/repack.c
index 82ab668272..27158a897b 100644
--- a/builtin/repack.c
+++ b/builtin/repack.c
@@ -733,7 +733,7 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
unsigned flags = 0;
if (git_env_bool(GIT_TEST_MULTI_PACK_INDEX_WRITE_BITMAP, 0))
flags |= MIDX_WRITE_BITMAP | MIDX_WRITE_REV_INDEX;
- write_midx_file(get_object_directory(), NULL, flags);
+ write_midx_file(get_object_directory(), NULL, NULL, flags);
}
string_list_clear(&names, 0);
diff --git a/midx.c b/midx.c
index 29d1d107b3..46ded7a4cf 100644
--- a/midx.c
+++ b/midx.c
@@ -970,7 +970,42 @@ static void bitmap_show_commit(struct commit *commit, void *_data)
data->commits[data->commits_nr++] = commit;
}
+static int read_refs_snapshot(const char *refs_snapshot,
+ struct rev_info *revs)
+{
+ struct strbuf buf = STRBUF_INIT;
+ struct object_id oid;
+ FILE *f = xfopen(refs_snapshot, "r");
+
+ while (strbuf_getline(&buf, f) != EOF) {
+ struct object *object;
+ int preferred = 0;
+ char *hex = buf.buf;
+ const char *end = NULL;
+
+ if (buf.len && *buf.buf == '+') {
+ preferred = 1;
+ hex = &buf.buf[1];
+ }
+
+ if (parse_oid_hex(hex, &oid, &end) < 0)
+ die(_("could not parse line: %s"), buf.buf);
+ if (*end)
+ die(_("malformed line: %s"), buf.buf);
+
+ object = parse_object_or_die(&oid, NULL);
+ if (preferred)
+ object->flags |= NEEDS_BITMAP;
+
+ add_pending_object(revs, object, "");
+ }
+
+ fclose(f);
+ return 0;
+}
+
static struct commit **find_commits_for_midx_bitmap(uint32_t *indexed_commits_nr_p,
+ const char *refs_snapshot,
struct write_midx_context *ctx)
{
struct rev_info revs;
@@ -979,8 +1014,12 @@ static struct commit **find_commits_for_midx_bitmap(uint32_t *indexed_commits_nr
cb.ctx = ctx;
repo_init_revisions(the_repository, &revs, NULL);
- setup_revisions(0, NULL, &revs, NULL);
- for_each_ref(add_ref_to_pending, &revs);
+ if (refs_snapshot) {
+ read_refs_snapshot(refs_snapshot, &revs);
+ } else {
+ setup_revisions(0, NULL, &revs, NULL);
+ for_each_ref(add_ref_to_pending, &revs);
+ }
/*
* Skipping promisor objects here is intentional, since it only excludes
@@ -1009,6 +1048,7 @@ static struct commit **find_commits_for_midx_bitmap(uint32_t *indexed_commits_nr
static int write_midx_bitmap(char *midx_name, unsigned char *midx_hash,
struct write_midx_context *ctx,
+ const char *refs_snapshot,
unsigned flags)
{
struct packing_data pdata;
@@ -1020,7 +1060,7 @@ static int write_midx_bitmap(char *midx_name, unsigned char *midx_hash,
prepare_midx_packing_data(&pdata, ctx);
- commits = find_commits_for_midx_bitmap(&commits_nr, ctx);
+ commits = find_commits_for_midx_bitmap(&commits_nr, refs_snapshot, ctx);
/*
* Build the MIDX-order index based on pdata.objects (which is already
@@ -1068,6 +1108,7 @@ static int write_midx_internal(const char *object_dir,
struct string_list *packs_to_include,
struct string_list *packs_to_drop,
const char *preferred_pack_name,
+ const char *refs_snapshot,
unsigned flags)
{
char *midx_name;
@@ -1361,7 +1402,8 @@ static int write_midx_internal(const char *object_dir,
if (flags & MIDX_WRITE_REV_INDEX)
write_midx_reverse_index(midx_name, midx_hash, &ctx);
if (flags & MIDX_WRITE_BITMAP) {
- if (write_midx_bitmap(midx_name, midx_hash, &ctx, flags) < 0) {
+ if (write_midx_bitmap(midx_name, midx_hash, &ctx,
+ refs_snapshot, flags) < 0) {
error(_("could not write multi-pack bitmap"));
result = 1;
goto cleanup;
@@ -1396,19 +1438,21 @@ static int write_midx_internal(const char *object_dir,
int write_midx_file(const char *object_dir,
const char *preferred_pack_name,
+ const char *refs_snapshot,
unsigned flags)
{
return write_midx_internal(object_dir, NULL, NULL, preferred_pack_name,
- flags);
+ refs_snapshot, flags);
}
int write_midx_file_only(const char *object_dir,
struct string_list *packs_to_include,
const char *preferred_pack_name,
+ const char *refs_snapshot,
unsigned flags)
{
return write_midx_internal(object_dir, packs_to_include, NULL,
- preferred_pack_name, flags);
+ preferred_pack_name, refs_snapshot, flags);
}
struct clear_midx_data {
@@ -1688,7 +1732,7 @@ int expire_midx_packs(struct repository *r, const char *object_dir, unsigned fla
free(count);
if (packs_to_drop.nr) {
- result = write_midx_internal(object_dir, NULL, &packs_to_drop, NULL, flags);
+ result = write_midx_internal(object_dir, NULL, &packs_to_drop, NULL, NULL, flags);
m = NULL;
}
@@ -1879,7 +1923,7 @@ int midx_repack(struct repository *r, const char *object_dir, size_t batch_size,
goto cleanup;
}
- result = write_midx_internal(object_dir, NULL, NULL, NULL, flags);
+ result = write_midx_internal(object_dir, NULL, NULL, NULL, NULL, flags);
m = NULL;
cleanup:
diff --git a/midx.h b/midx.h
index aefa371c90..dc37b94ea1 100644
--- a/midx.h
+++ b/midx.h
@@ -62,8 +62,8 @@ int fill_midx_entry(struct repository *r, const struct object_id *oid, struct pa
int midx_contains_pack(struct multi_pack_index *m, const char *idx_or_pack_name);
int prepare_multi_pack_index_one(struct repository *r, const char *object_dir, int local);
-int write_midx_file(const char *object_dir, const char *preferred_pack_name, unsigned flags);
-int write_midx_file_only(const char *object_dir, struct string_list *packs_to_include, const char *preferred_pack_name, unsigned flags);
+int write_midx_file(const char *object_dir, const char *preferred_pack_name, const char *refs_snapshot, unsigned flags);
+int write_midx_file_only(const char *object_dir, struct string_list *packs_to_include, const char *preferred_pack_name, const char *refs_snapshot, unsigned flags);
void clear_midx_file(struct repository *r);
int verify_midx_file(struct repository *r, const char *object_dir, unsigned flags);
int expire_midx_packs(struct repository *r, const char *object_dir, unsigned flags);
diff --git a/t/t5326-multi-pack-bitmaps.sh b/t/t5326-multi-pack-bitmaps.sh
index 4ad7c2c969..069dab3e17 100755
--- a/t/t5326-multi-pack-bitmaps.sh
+++ b/t/t5326-multi-pack-bitmaps.sh
@@ -283,4 +283,86 @@ test_expect_success 'pack.preferBitmapTips' '
)
'
+test_expect_success 'writing a bitmap with --refs-snapshot' '
+ git init repo &&
+ test_when_finished "rm -fr repo" &&
+ (
+ cd repo &&
+
+ test_commit one &&
+ test_commit two &&
+
+ git rev-parse one >snapshot &&
+
+ git repack -ad &&
+
+ # First, write a MIDX which see both refs/tags/one and
+ # refs/tags/two (causing both of those commits to receive
+ # bitmaps).
+ git multi-pack-index write --bitmap &&
+
+ test_path_is_file $midx &&
+ test_path_is_file $midx-$(midx_checksum $objdir).bitmap &&
+
+ test-tool bitmap list-commits | sort >bitmaps &&
+ grep "$(git rev-parse one)" bitmaps &&
+ grep "$(git rev-parse two)" bitmaps &&
+
+ rm -fr $midx-$(midx_checksum $objdir).bitmap &&
+ rm -fr $midx-$(midx_checksum $objdir).rev &&
+ rm -fr $midx &&
+
+ # Then again, but with a refs snapshot which only sees
+ # refs/tags/one.
+ git multi-pack-index write --bitmap --refs-snapshot=snapshot &&
+
+ test_path_is_file $midx &&
+ test_path_is_file $midx-$(midx_checksum $objdir).bitmap &&
+
+ test-tool bitmap list-commits | sort >bitmaps &&
+ grep "$(git rev-parse one)" bitmaps &&
+ ! grep "$(git rev-parse two)" bitmaps
+ )
+'
+
+test_expect_success 'write a bitmap with --refs-snapshot (preferred tips)' '
+ git init repo &&
+ test_when_finished "rm -fr repo" &&
+ (
+ cd repo &&
+
+ test_commit_bulk --message="%s" 103 &&
+
+ git log --format="%H" >commits.raw &&
+ sort <commits.raw >commits &&
+
+ git log --format="create refs/tags/%s %H" HEAD >refs &&
+ git update-ref --stdin <refs &&
+
+ git multi-pack-index write --bitmap &&
+ test_path_is_file $midx &&
+ test_path_is_file $midx-$(midx_checksum $objdir).bitmap &&
+
+ test-tool bitmap list-commits | sort >bitmaps &&
+ comm -13 bitmaps commits >before &&
+ test_line_count = 1 before &&
+
+ (
+ grep -vf before commits.raw &&
+ # mark missing commits as preferred
+ sed "s/^/+/" before
+ ) >snapshot &&
+
+ rm -fr $midx-$(midx_checksum $objdir).bitmap &&
+ rm -fr $midx-$(midx_checksum $objdir).rev &&
+ rm -fr $midx &&
+
+ git multi-pack-index write --bitmap --refs-snapshot=snapshot &&
+ test-tool bitmap list-commits | sort >bitmaps &&
+ comm -13 bitmaps commits >after &&
+
+ ! test_cmp before after
+ )
+'
+
test_done
Taylor Blau
