Cache ValidLinkableSpecResolver._get_joined_elements() (#1435)

This PR caches retrieval of the joined elements of a measure as it can
be called repeatedly when resolving the group-by items for a derived
metric (or a simple metric that is common to many saved queries).

metricflow-semantics/metricflow_semantics/model/semantics/linkable_spec_resolver.py

@@ -82,18 +82,21 @@ def __init__(
 
         # Map measures / entities to semantic models that contain them.
         self._entity_to_semantic_model: Dict[str, List[SemanticModel]] = defaultdict(list)
-        self._measure_to_semantic_model: Dict[str, List[SemanticModel]] = defaultdict(list)
-
+        self._semantic_model_reference_to_semantic_model: Dict[SemanticModelReference, SemanticModel] = {}
         for semantic_model in self._semantic_models:
             for entity in semantic_model.entities:
                 self._entity_to_semantic_model[entity.reference.element_name].append(semantic_model)
+            self._semantic_model_reference_to_semantic_model[semantic_model.reference] = semantic_model
 
         self._metric_to_linkable_element_sets: Dict[str, List[LinkableElementSet]] = {}
         self._metric_references_to_metrics: Dict[MetricReference, Metric] = {}
         self._joinable_metrics_for_entities: Dict[EntityReference, Set[MetricSubqueryJoinPathElement]] = defaultdict(
             set
         )
 
+        # Cache for `_get_joined_elements()`.
+        self._semantic_model_reference_to_joined_elements: Dict[SemanticModelReference, LinkableElementSet] = {}
+
         start_time = time.time()
         for metric in self._semantic_manifest.metrics:
             self._metric_references_to_metrics[MetricReference(metric.name)] = metric
@@ -526,8 +529,20 @@ def _get_metric_time_elements(self, measure_reference: Optional[MeasureReference
             }
         )
 
-    def _get_joined_elements(self, measure_semantic_model: SemanticModel) -> LinkableElementSet:
+    def _get_joined_elements(self, measure_semantic_model_reference: SemanticModelReference) -> LinkableElementSet:
         """Get the elements that can be generated by joining other models to the given model."""
+        result = self._semantic_model_reference_to_joined_elements.get(measure_semantic_model_reference)
+        if result is not None:
+            return result
+
+        result = self._get_joined_elements_without_cache(measure_semantic_model_reference)
+        self._semantic_model_reference_to_joined_elements[measure_semantic_model_reference] = result
+        return result
+
+    def _get_joined_elements_without_cache(
+        self, measure_semantic_model_reference: SemanticModelReference
+    ) -> LinkableElementSet:
+        measure_semantic_model = self._semantic_model_reference_to_semantic_model[measure_semantic_model_reference]
         # Create single-hop elements
         join_paths = []
         for entity in measure_semantic_model.entities:
@@ -596,7 +611,7 @@ def _get_linkable_element_set_for_measure(
             metrics_linked_to_semantic_model = LinkableElementSet()
 
         metric_time_elements = self._get_metric_time_elements(measure_reference)
-        joined_elements = self._get_joined_elements(measure_semantic_model)
+        joined_elements = self._get_joined_elements(measure_semantic_model.reference)
 
         return LinkableElementSet.merge_by_path_key(
             (