[PATCH] builtin/refs: add '--skip-reflog' flag to bypass reflog migration

[Karthik Nayak <karthik.188@gmail.com>]

The 'git-refs(1)' migrate subcommand, which transfers repositories
between reference backends, currently migrates reflogs by default as of
In 246cebe320 (refs: add support for migrating reflogs, 2024-12-16).
While this behavior is desirable for most client-side repositories,
server-side repositories typically don't use reflogs and the migration
of these entries is unnecessary overhead.

Add a '--skip-reflog' flag to the migrate subcommand to make reflog
migration optional. This is particularly useful for server-side
migrations where reflogs are not needed, improving migration performance
in these scenarios.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
---
---
 builtin/refs.c          |  3 +++
 refs.c                  |  8 +++++---
 refs.h                  |  5 ++++-
 t/t1460-refs-migrate.sh | 17 +++++++++++++++--
 4 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/builtin/refs.c b/builtin/refs.c
index a29f19583474518ee0942ea53c39cbdf9661c5e2..30be0254c14dd3d07693d70c25dddc9990756e9c 100644
--- a/builtin/refs.c
+++ b/builtin/refs.c
@@ -30,6 +30,9 @@ static int cmd_refs_migrate(int argc, const char **argv, const char *prefix,
 		OPT_BIT(0, "dry-run", &flags,
 			N_("perform a non-destructive dry-run"),
 			REPO_MIGRATE_REF_STORAGE_FORMAT_DRYRUN),
+		OPT_BIT(0, "skip-reflog", &flags,
+			N_("skip migrating reflogs"),
+			REPO_MIGRATE_REF_STORAGE_FORMAT_SKIP_REFLOG),
 		OPT_END(),
 	};
 	struct strbuf errbuf = STRBUF_INIT;
diff --git a/refs.c b/refs.c
index f4094a326a9f88f979654b668cc9c3d27d83cb5d..5e8f5c06fa68d16c93ee11edd9742995eea994b6 100644
--- a/refs.c
+++ b/refs.c
@@ -3035,9 +3035,11 @@ int repo_migrate_ref_storage_format(struct repository *repo,
 	if (ret < 0)
 		goto done;
 
-	ret = refs_for_each_reflog(old_refs, migrate_one_reflog, &data);
-	if (ret < 0)
-		goto done;
+	if (!(flags & REPO_MIGRATE_REF_STORAGE_FORMAT_SKIP_REFLOG)) {
+		ret = refs_for_each_reflog(old_refs, migrate_one_reflog, &data);
+		if (ret < 0)
+			goto done;
+	}
 
 	ret = ref_transaction_commit(transaction, errbuf);
 	if (ret < 0)
diff --git a/refs.h b/refs.h
index a0cdd99250e8286b55808b697b0a94afac5d8319..ccee8fc6705e6e93a1c6234e7395180f8dfd815b 100644
--- a/refs.h
+++ b/refs.h
@@ -1157,8 +1157,11 @@ int is_pseudo_ref(const char *refname);
  *   - REPO_MIGRATE_REF_STORAGE_FORMAT_DRYRUN: perform a dry-run migration
  *     without touching the main repository. The result will be written into a
  *     temporary ref storage directory.
+ *
+ *   - REPO_MIGRATE_REF_STORAGE_FORMAT_SKIP_REFLOG: skip migration of reflogs.
  */
-#define REPO_MIGRATE_REF_STORAGE_FORMAT_DRYRUN (1 << 0)
+#define REPO_MIGRATE_REF_STORAGE_FORMAT_DRYRUN      (1 << 0)
+#define REPO_MIGRATE_REF_STORAGE_FORMAT_SKIP_REFLOG (1 << 1)
 
 /*
  * Migrate the ref storage format used by the repository to the
diff --git a/t/t1460-refs-migrate.sh b/t/t1460-refs-migrate.sh
index a6d9b35a46eb59350aa0d59d982a2fbfaecf1448..9059d4c4121842a9d2e77dc4e54c537eeff8afab 100755
--- a/t/t1460-refs-migrate.sh
+++ b/t/t1460-refs-migrate.sh
@@ -9,14 +9,16 @@ export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
 # Migrate the provided repository from one format to the other and
 # verify that the references and logs are migrated over correctly.
-# Usage: test_migration <repo> <format> <skip_reflog_verify>
+# Usage: test_migration <repo> <format> <skip_reflog_verify> <...options>
 #   <repo> is the relative path to the repo to be migrated.
 #   <format> is the ref format to be migrated to.
 #   <skip_reflog_verify> (true or false) whether to skip reflog verification.
+#   <...options> are other options be passed directly to 'git refs migrate'.
 test_migration () {
 	repo=$1 &&
 	format=$2 &&
 	skip_reflog_verify=${3:-false} &&
+	shift $(( $# >= 3 ? 3 : 2 )) &&
 	git -C "$repo" for-each-ref --include-root-refs \
 		--format='%(refname) %(objectname) %(symref)' >expect &&
 	if ! $skip_reflog_verify
@@ -25,7 +27,7 @@ test_migration () {
 	   git -C "$repo" reflog list >expect_log_list
 	fi &&
 
-	git -C "$repo" refs migrate --ref-format="$2" &&
+	git -C "$repo" refs migrate --ref-format="$format" $@ &&
 
 	git -C "$repo" for-each-ref --include-root-refs \
 		--format='%(refname) %(objectname) %(symref)' >actual &&
@@ -241,6 +243,17 @@ do
 				test_cmp expect.reflog actual.reflog
 			)
 		'
+
+		test_expect_success "$from_format -> $to_format: skip reflog with --skip-reflog" '
+			test_when_finished "rm -rf repo" &&
+			git init --ref-format=$from_format repo &&
+			test_commit -C repo initial &&
+			# we see that the repository contains reflogs.
+			test 2 = $(git -C repo reflog --all | wc -l) &&
+			test_migration repo "$to_format" true --skip-reflog &&
+			# there should be no reflogs post migration.
+			test 0 = $(git -C repo reflog --all | wc -l)
+		'
 	done
 done
 

---

base-commit: bc204b742735ae06f65bb20291c95985c9633b7f
change-id: 20250207-477-refs-migrate-add-a-flag-to-ignore-reflogs-during-migration-8066f6df50ac

Thanks
- Karthik