chore: Make MatchingEngineIndexConfig's algorithmConfig optional

google/cloud/aiplatform/matching_engine/matching_engine_index.py

@@ -596,10 +596,15 @@ def create_tree_ah_index(
 
         """
 
-        algorithm_config = matching_engine_index_config.TreeAhConfig(
-            leaf_node_embedding_count=leaf_node_embedding_count,
-            leaf_nodes_to_search_percent=leaf_nodes_to_search_percent,
-        )
+        algorithm_config = None
+        if (
+            leaf_node_embedding_count is not None
+            or leaf_nodes_to_search_percent is not None
+        ):
+            algorithm_config = matching_engine_index_config.TreeAhConfig(
+                leaf_node_embedding_count=leaf_node_embedding_count,
+                leaf_nodes_to_search_percent=leaf_nodes_to_search_percent,
+            )
 
         config = matching_engine_index_config.MatchingEngineIndexConfig(
             dimensions=dimensions,

google/cloud/aiplatform/matching_engine/matching_engine_index_config.py

@@ -120,7 +120,7 @@ class MatchingEngineIndexConfig:
         dimensions (int):
             Required. The number of dimensions of the input vectors.
         algorithm_config (AlgorithmConfig):
-            Required. The configuration with regard to the algorithms used for efficient search.
+            Optional. The configuration with regard to the algorithms used for efficient search.
         approximate_neighbors_count (int):
             Optional. The default number of neighbors to find via approximate search before exact reordering is
             performed. Exact reordering is a procedure where results returned by an
@@ -139,7 +139,7 @@ class MatchingEngineIndexConfig:
     """
 
     dimensions: int
-    algorithm_config: AlgorithmConfig
+    algorithm_config: Optional[AlgorithmConfig] = None
     approximate_neighbors_count: Optional[int] = None
     distance_measure_type: Optional[DistanceMeasureType] = None
     feature_norm_type: Optional[FeatureNormType] = None
@@ -153,10 +153,13 @@ def as_dict(self) -> Dict[str, Any]:
         """
         res = {
             "dimensions": self.dimensions,
-            "algorithmConfig": self.algorithm_config.as_dict(),
             "approximateNeighborsCount": self.approximate_neighbors_count,
             "distanceMeasureType": self.distance_measure_type,
             "featureNormType": self.feature_norm_type,
             "shardSize": self.shard_size,
         }
+        if self.algorithm_config:
+            res["algorithmConfig"] = self.algorithm_config.as_dict()
+        else:
+            res["algorithmConfig"] = None
         return res

tests/unit/aiplatform/test_matching_engine_index.py

@@ -618,6 +618,45 @@ def test_create_tree_ah_index_backward_compatibility(self, create_index_mock):
             timeout=None,
         )
 
+    @pytest.mark.usefixtures("get_index_mock")
+    def test_create_tree_ah_index_empty_algorithm_config(self, create_index_mock):
+        aiplatform.init(project=_TEST_PROJECT)
+
+        aiplatform.MatchingEngineIndex.create_tree_ah_index(
+            display_name=_TEST_INDEX_DISPLAY_NAME,
+            contents_delta_uri=_TEST_CONTENTS_DELTA_URI,
+            dimensions=_TEST_INDEX_CONFIG_DIMENSIONS,
+            approximate_neighbors_count=_TEST_INDEX_APPROXIMATE_NEIGHBORS_COUNT,
+            distance_measure_type=_TEST_INDEX_DISTANCE_MEASURE_TYPE.value,
+            feature_norm_type=_TEST_INDEX_FEATURE_NORM_TYPE.value,
+            description=_TEST_INDEX_DESCRIPTION,
+            labels=_TEST_LABELS,
+        )
+
+        expected = gca_index.Index(
+            display_name=_TEST_INDEX_DISPLAY_NAME,
+            metadata={
+                "config": {
+                    "algorithmConfig": None,
+                    "dimensions": _TEST_INDEX_CONFIG_DIMENSIONS,
+                    "approximateNeighborsCount": _TEST_INDEX_APPROXIMATE_NEIGHBORS_COUNT,
+                    "distanceMeasureType": _TEST_INDEX_DISTANCE_MEASURE_TYPE,
+                    "featureNormType": _TEST_INDEX_FEATURE_NORM_TYPE,
+                    "shardSize": None,
+                },
+                "contentsDeltaUri": _TEST_CONTENTS_DELTA_URI,
+            },
+            description=_TEST_INDEX_DESCRIPTION,
+            labels=_TEST_LABELS,
+        )
+
+        create_index_mock.assert_called_once_with(
+            parent=_TEST_PARENT,
+            index=expected,
+            metadata=_TEST_REQUEST_METADATA,
+            timeout=None,
+        )
+
     @pytest.mark.usefixtures("get_index_mock")
     @pytest.mark.parametrize("sync", [True, False])
     @pytest.mark.parametrize(