goto cleanup;
}
backend_data->packed_refs_locked = 1;
- ret = ref_transaction_prepare(packed_transaction, err);
+
+ if (is_packed_transaction_needed(refs->packed_ref_store,
+ packed_transaction)) {
+ ret = ref_transaction_prepare(packed_transaction, err);
+ } else {
+ /*
+ * We can skip rewriting the `packed-refs`
+ * file. But we do need to leave it locked, so
+ * that somebody else doesn't pack a reference
+ * that we are trying to delete.
+ */
+ if (ref_transaction_abort(packed_transaction, err)) {
+ ret = TRANSACTION_GENERIC_ERROR;
+ goto cleanup;
+ }
+ backend_data->packed_transaction = NULL;
+ }
}
cleanup:
return -1;
}
+int is_packed_transaction_needed(struct ref_store *ref_store,
+ struct ref_transaction *transaction)
+{
+ struct packed_ref_store *refs = packed_downcast(
+ ref_store,
+ REF_STORE_READ,
+ "is_packed_transaction_needed");
+ struct strbuf referent = STRBUF_INIT;
+ size_t i;
+ int ret;
+
+ if (!is_lock_file_locked(&refs->lock))
+ BUG("is_packed_transaction_needed() called while unlocked");
+
+ /*
+ * We're only going to bother returning false for the common,
+ * trivial case that references are only being deleted, their
+ * old values are not being checked, and the old `packed-refs`
+ * file doesn't contain any of those reference(s). This gives
+ * false positives for some other cases that could
+ * theoretically be optimized away:
+ *
+ * 1. It could be that the old value is being verified without
+ * setting a new value. In this case, we could verify the
+ * old value here and skip the update if it agrees. If it
+ * disagrees, we could either let the update go through
+ * (the actual commit would re-detect and report the
+ * problem), or come up with a way of reporting such an
+ * error to *our* caller.
+ *
+ * 2. It could be that a new value is being set, but that it
+ * is identical to the current packed value of the
+ * reference.
+ *
+ * Neither of these cases will come up in the current code,
+ * because the only caller of this function passes to it a
+ * transaction that only includes `delete` updates with no
+ * `old_id`. Even if that ever changes, false positives only
+ * cause an optimization to be missed; they do not affect
+ * correctness.
+ */
+
+ /*
+ * Start with the cheap checks that don't require old
+ * reference values to be read:
+ */
+ for (i = 0; i < transaction->nr; i++) {
+ struct ref_update *update = transaction->updates[i];
+
+ if (update->flags & REF_HAVE_OLD)
+ /* Have to check the old value -> needed. */
+ return 1;
+
+ if ((update->flags & REF_HAVE_NEW) && !is_null_oid(&update->new_oid))
+ /* Have to set a new value -> needed. */
+ return 1;
+ }
+
+ /*
+ * The transaction isn't checking any old values nor is it
+ * setting any nonzero new values, so it still might be able
+ * to be skipped. Now do the more expensive check: the update
+ * is needed if any of the updates is a delete, and the old
+ * `packed-refs` file contains a value for that reference.
+ */
+ ret = 0;
+ for (i = 0; i < transaction->nr; i++) {
+ struct ref_update *update = transaction->updates[i];
+ unsigned int type;
+ struct object_id oid;
+
+ if (!(update->flags & REF_HAVE_NEW))
+ /*
+ * This reference isn't being deleted -> not
+ * needed.
+ */
+ continue;
+
+ if (!refs_read_raw_ref(ref_store, update->refname,
+ oid.hash, &referent, &type) ||
+ errno != ENOENT) {
+ /*
+ * We have to actually delete that reference
+ * -> this transaction is needed.
+ */
+ ret = 1;
+ break;
+ }
+ }
+
+ strbuf_release(&referent);
+ return ret;
+}
+
struct packed_transaction_backend_data {
/* True iff the transaction owns the packed-refs lock. */
int own_lock;
void packed_refs_unlock(struct ref_store *ref_store);
int packed_refs_is_locked(struct ref_store *ref_store);
+/*
+ * Return true if `transaction` really needs to be carried out against
+ * the specified packed_ref_store, or false if it can be skipped
+ * (i.e., because it is an obvious NOOP). `ref_store` must be locked
+ * before calling this function.
+ */
+int is_packed_transaction_needed(struct ref_store *ref_store,
+ struct ref_transaction *transaction);
+
#endif /* REFS_PACKED_BACKEND_H */
--- /dev/null
+#!/bin/sh
+
+test_description='avoid rewriting packed-refs unnecessarily'
+
+. ./test-lib.sh
+
+# Add an identifying mark to the packed-refs file header line. This
+# shouldn't upset readers, and it should be omitted if the file is
+# ever rewritten.
+mark_packed_refs () {
+ sed -e "s/^\(#.*\)/\1 t1409 /" <.git/packed-refs >.git/packed-refs.new &&
+ mv .git/packed-refs.new .git/packed-refs
+}
+
+# Verify that the packed-refs file is still marked.
+check_packed_refs_marked () {
+ grep -q '^#.* t1409 ' .git/packed-refs
+}
+
+test_expect_success 'setup' '
+ git commit --allow-empty -m "Commit A" &&
+ A=$(git rev-parse HEAD) &&
+ git commit --allow-empty -m "Commit B" &&
+ B=$(git rev-parse HEAD) &&
+ git commit --allow-empty -m "Commit C" &&
+ C=$(git rev-parse HEAD)
+'
+
+test_expect_success 'do not create packed-refs file gratuitously' '
+ test_must_fail test -f .git/packed-refs &&
+ git update-ref refs/heads/foo $A &&
+ test_must_fail test -f .git/packed-refs &&
+ git update-ref refs/heads/foo $B &&
+ test_must_fail test -f .git/packed-refs &&
+ git update-ref refs/heads/foo $C $B &&
+ test_must_fail test -f .git/packed-refs &&
+ git update-ref -d refs/heads/foo &&
+ test_must_fail test -f .git/packed-refs
+'
+
+test_expect_success 'check that marking the packed-refs file works' '
+ git for-each-ref >expected &&
+ git pack-refs --all &&
+ mark_packed_refs &&
+ check_packed_refs_marked &&
+ git for-each-ref >actual &&
+ test_cmp expected actual &&
+ git pack-refs --all &&
+ test_must_fail check_packed_refs_marked &&
+ git for-each-ref >actual2 &&
+ test_cmp expected actual2
+'
+
+test_expect_success 'leave packed-refs untouched on update of packed' '
+ git update-ref refs/heads/packed-update $A &&
+ git pack-refs --all &&
+ mark_packed_refs &&
+ git update-ref refs/heads/packed-update $B &&
+ check_packed_refs_marked
+'
+
+test_expect_success 'leave packed-refs untouched on checked update of packed' '
+ git update-ref refs/heads/packed-checked-update $A &&
+ git pack-refs --all &&
+ mark_packed_refs &&
+ git update-ref refs/heads/packed-checked-update $B $A &&
+ check_packed_refs_marked
+'
+
+test_expect_success 'leave packed-refs untouched on verify of packed' '
+ git update-ref refs/heads/packed-verify $A &&
+ git pack-refs --all &&
+ mark_packed_refs &&
+ echo "verify refs/heads/packed-verify $A" | git update-ref --stdin &&
+ check_packed_refs_marked
+'
+
+test_expect_success 'touch packed-refs on delete of packed' '
+ git update-ref refs/heads/packed-delete $A &&
+ git pack-refs --all &&
+ mark_packed_refs &&
+ git update-ref -d refs/heads/packed-delete &&
+ test_must_fail check_packed_refs_marked
+'
+
+test_expect_success 'leave packed-refs untouched on update of loose' '
+ git pack-refs --all &&
+ git update-ref refs/heads/loose-update $A &&
+ mark_packed_refs &&
+ git update-ref refs/heads/loose-update $B &&
+ check_packed_refs_marked
+'
+
+test_expect_success 'leave packed-refs untouched on checked update of loose' '
+ git pack-refs --all &&
+ git update-ref refs/heads/loose-checked-update $A &&
+ mark_packed_refs &&
+ git update-ref refs/heads/loose-checked-update $B $A &&
+ check_packed_refs_marked
+'
+
+test_expect_success 'leave packed-refs untouched on verify of loose' '
+ git pack-refs --all &&
+ git update-ref refs/heads/loose-verify $A &&
+ mark_packed_refs &&
+ echo "verify refs/heads/loose-verify $A" | git update-ref --stdin &&
+ check_packed_refs_marked
+'
+
+test_expect_success 'leave packed-refs untouched on delete of loose' '
+ git pack-refs --all &&
+ git update-ref refs/heads/loose-delete $A &&
+ mark_packed_refs &&
+ git update-ref -d refs/heads/loose-delete &&
+ check_packed_refs_marked
+'
+
+test_done