storage: prepare for kv.atomic_replication_changes=true

pkg/roachpb/api.proto

@@ -720,6 +720,7 @@ message AdminUnsplitResponse {
 // now encompass all keys from its original start key to the end key
 // of the subsumed range. If AdminMerge is called on the final range
 // in the key space, it is a noop.
+// The request must be addressed to the start key of the left hand side.
 message AdminMergeRequest {
   option (gogoproto.equal) = true;
 

pkg/roachpb/metadata.go

@@ -100,6 +100,24 @@ func (a Attributes) String() string {
 	return strings.Join(a.Attrs, ",")
 }
 
+// NewRangeDescriptor returns a RangeDescriptor populated from the input.
+func NewRangeDescriptor(
+	rangeID RangeID, start, end RKey, replicas ReplicaDescriptors,
+) *RangeDescriptor {
+	repls := append([]ReplicaDescriptor(nil), replicas.All()...)
+	for i := range repls {
+		repls[i].ReplicaID = ReplicaID(i + 1)
+	}
+	desc := &RangeDescriptor{
+		RangeID:       rangeID,
+		StartKey:      start,
+		EndKey:        end,
+		NextReplicaID: ReplicaID(len(repls) + 1),
+	}
+	desc.SetReplicas(MakeReplicaDescriptors(repls))
+	return desc
+}
+
 // RSpan returns the RangeDescriptor's resolved span.
 func (r *RangeDescriptor) RSpan() RSpan {
 	return RSpan{Key: r.StartKey, EndKey: r.EndKey}

pkg/storage/client_merge_test.go

@@ -2259,7 +2259,7 @@ func TestStoreRangeMergeDeadFollowerDuringTxn(t *testing.T) {
 
 	args := adminMergeArgs(lhsDesc.StartKey.AsRawKey())
 	_, pErr := client.SendWrapped(ctx, store0.TestSender(), args)
-	expErr := "merge of range into .* failed: waiting for all right-hand replicas to catch up"
+	expErr := "merge failed: waiting for all right-hand replicas to catch up"
 	if !testutils.IsPError(pErr, expErr) {
 		t.Fatalf("expected %q error, but got %v", expErr, pErr)
 	}

pkg/storage/merge_queue.go

@@ -353,7 +353,9 @@ func (mq *mergeQueue) process(
 		humanizeutil.IBytes(mergedStats.Total()),
 		mergedQPS,
 	)
-	_, pErr := lhsRepl.AdminMerge(ctx, roachpb.AdminMergeRequest{}, reason)
+	_, pErr := lhsRepl.AdminMerge(ctx, roachpb.AdminMergeRequest{
+		RequestHeader: roachpb.RequestHeader{Key: lhsRepl.Desc().StartKey.AsRawKey()},
+	}, reason)
 	switch err := pErr.GoError(); err.(type) {
 	case nil:
 	case *roachpb.ConditionFailedError: