message: once per materialize
diff: @@ -62,6 +62,7 @@ struct AltrepRelationWrapper {
  MaterializedQueryResult *GetQueryResult() {
  if (!res) {
  + Rprintf("materializing...\n");
  res = rel->Execute();
  if (res->HasError()) {
  Rf_error(res->GetError().c_str());
  @@ -101,7 +102,6 @@ struct AltrepVectorWrapper {
  void *Dataptr() {
  if (transformed_vector.data() == R_NilValue) {
  - R_ShowMessage("Materializing...");
  auto res = rel->GetQueryResult();
  RProtector r_varvalue;
  transformed_vector = duckdb_r_allocate(res->types[column_index], r_varvalue, res->RowCount());
  