guard against multiple info schemas in get_catalog_by_relations

dbt/adapters/spark/impl.py

@@ -386,22 +386,23 @@ def get_catalog_by_relations(
         self, manifest: Manifest, relations: Set[BaseRelation]
     ) -> Tuple[agate.Table, List[Exception]]:
         relations_by_info_schema = self._get_catalog_relations_by_info_schema(relations)
+        if len(relations_by_info_schema) != 1:
+            raise dbt.exceptions.CompilationError(
+                f"Expected exactly one information schema in get_catalog_by_relations, "
+                f"found {list(relations_by_info_schema)}"
+            )
 
         with executor(self.config) as tpe:
-            futures: List[Future[agate.Table]] = []
-            for info_schema, relations_in_info_schema in relations_by_info_schema.items():
-                for relation in relations_in_info_schema:
-                    futures.append(
-                        tpe.submit_connected(
-                            self,
-                            relation.schema,
-                            self._get_one_catalog_by_relations,
-                            info_schema,
-                            [relation],
-                            manifest,
-                        )
-                    )
-            catalogs, exceptions = catch_as_completed(futures)
+            info_schema, relations_in_info_schema = set(relations_by_info_schema.items()).pop()
+            future = tpe.submit_connected(
+                self,
+                info_schema.database,
+                self._get_one_catalog_by_relations,
+                info_schema,
+                relations_in_info_schema,
+                manifest,
+            )
+            catalogs, exceptions = catch_as_completed([future])
         return catalogs, exceptions
 
     def _get_one_catalog(