Add last replica ID to GetRangeDebugInfo (#11168)

Author: vanja-p

enterprise/server/raft/store/store.go

@@ -582,6 +582,13 @@ func (s *Store) queryForMetarange(ctx context.Context) {
 }
 func (s *Store) GetRangeDebugInfo(ctx context.Context, req *rfpb.GetRangeDebugInfoRequest) (*rfpb.GetRangeDebugInfoResponse, error) {
 	leaderID, term, valid, _ := s.nodeHost.GetLeaderID(req.GetRangeId())
+	lastReplicaIDKey := keys.MakeKey(constants.LastReplicaIDKeyPrefix, []byte(fmt.Sprintf("%d", req.GetRangeId())))
+	lastReplicaIDBytes, err := s.sender.DirectRead(ctx, lastReplicaIDKey)
+	if err != nil {
+		return nil, status.WrapErrorf(err, "failed to read last replica ID for range %d with key %q", req.GetRangeId(), lastReplicaIDKey)
+	} else if len(lastReplicaIDBytes) != 8 {
+		return nil, status.InternalErrorf("failed to read last replica ID for range %d with key %q: expected 8 bytes, got %d", req.GetRangeId(), lastReplicaIDKey, len(lastReplicaIDBytes))
+	}
 	rsp := &rfpb.GetRangeDebugInfoResponse{
 		Nhid:            s.NHID(),
 		RangeDescriptor: s.lookupRange(req.GetRangeId()),
@@ -591,6 +598,7 @@ func (s *Store) GetRangeDebugInfo(ctx context.Context, req *rfpb.GetRangeDebugIn
 			Term:     term,
 			Valid:    valid,
 		},
+		LastReplicaId: bytesToUint64(lastReplicaIDBytes),
 	}
 	// Fetch the range descriptor from meta range to make sure it's the most-up-to-date.
 	ranges, err := s.sender.LookupRangeDescriptorsByIDs(ctx, []uint64{req.GetRangeId()})

proto/raft.proto

@@ -712,6 +712,7 @@ message GetRangeDebugInfoResponse {
   RaftLeaderInfo leader = 3;
   bool has_lease = 4;
   RaftMembership membership = 5;
+  uint64 last_replica_id = 7;
 }
 
 message RangeDescriptorChange {