doc(restore): add docs for mutations in between incremental restores

dgraphtest/local_cluster.go

@@ -73,7 +73,7 @@ func (u UpgradeStrategy) String() string {
 	case BackupRestore:
 		return "backup-restore"
 	case InPlace:
-		return "stop-start"
+		return "in-place"
 	case ExportImport:
 		return "export-import"
 	default:

systest/integration2/incremental_restore_test.go

@@ -87,5 +87,12 @@ func TestIncrementalRestore(t *testing.T) {
 			sort.Ints(data.Q[0].Money)
 			require.Equal(t, uids[j-1:i], data.Q[0].Money)
 		}
+
+		// Even when we do an in between mutations, it makes no difference.
+		// Incremental restore overwrites any data written in between.
+		if i == 10 {
+			_, err := gc.Mutate(&api.Mutation{SetNquads: []byte(`<10> <money> "4" .`), CommitNow: true})
+			require.NoError(t, err)
+		}
 	}
 }

worker/online_restore.go

@@ -371,6 +371,10 @@ func handleRestoreProposal(ctx context.Context, req *pb.RestoreRequest, pidx uin
 		if err := pstore.DropPrefix(dropAttrs...); err != nil {
 			return errors.Wrap(err, "failed to reduce incremental restore map")
 		}
+		// If there are any writes done after last incremental restore on badger DB,
+		// the restore or incremental restore will lose that data. This happens because
+		// the timestamp of the in between mutations etc will be lower than the timestamp
+		// of this incremental restore that we may be doing now (if it is one).
 		if err := sw.PrepareIncremental(); err != nil {
 			return errors.Wrapf(err, "while preparing DB")
 		}