Support fixed features in Service API (#2372)

Summary:

Add the possibility of specifying some `FixedFeatures` as `fixed_features` in `AxClient.get_next_trial` and `AxClient.get_next_trials` which is currently only possible with the developer API.

Reviewed By: saitcakmak

Differential Revision: D56068035

ax/service/ax_client.py

@@ -495,7 +495,10 @@ def set_search_space(
         wrap_error_message_in=CHOLESKY_ERROR_ANNOTATION,
     )
     def get_next_trial(
-        self, ttl_seconds: Optional[int] = None, force: bool = False
+        self,
+        ttl_seconds: Optional[int] = None,
+        force: bool = False,
+        fixed_features: Optional[FixedFeatures] = None,
     ) -> Tuple[TParameterization, int]:
         """
         Generate trial with the next set of parameters to try in the iteration process.
@@ -508,6 +511,9 @@ def get_next_trial(
                 failed properly.
             force: If set to True, this function will bypass the global stopping
                 strategy's decision and generate a new trial anyway.
+            fixed_features: A FixedFeatures object containing any
+                features that should be fixed at specified values during
+                generation.
 
         Returns:
             Tuple of trial parameterization, trial index
@@ -530,7 +536,10 @@ def get_next_trial(
 
         try:
             trial = self.experiment.new_trial(
-                generator_run=self._gen_new_generator_run(), ttl_seconds=ttl_seconds
+                generator_run=self._gen_new_generator_run(
+                    fixed_features=fixed_features
+                ),
+                ttl_seconds=ttl_seconds,
             )
         except MaxParallelismReachedException as e:
             if self._early_stopping_strategy is not None:
@@ -580,7 +589,10 @@ def get_current_trial_generation_limit(self) -> Tuple[int, bool]:
         return self.generation_strategy.current_generator_run_limit()
 
     def get_next_trials(
-        self, max_trials: int, ttl_seconds: Optional[int] = None
+        self,
+        max_trials: int,
+        ttl_seconds: Optional[int] = None,
+        fixed_features: Optional[FixedFeatures] = None,
     ) -> Tuple[Dict[int, TParameterization], bool]:
         """Generate as many trials as currently possible.
 
@@ -597,6 +609,9 @@ def get_next_trials(
             ttl_seconds: If specified, will consider the trial failed after this
                 many seconds. Used to detect dead trials that were not marked
                 failed properly.
+            fixed_features: A FixedFeatures object containing any
+                features that should be fixed at specified values during
+                generation.
 
         Returns: two-item tuple of:
               - mapping from trial indices to parameterizations in those trials,
@@ -616,7 +631,9 @@ def get_next_trials(
         trials_dict = {}
         for _ in range(max_trials):
             try:
-                params, trial_index = self.get_next_trial(ttl_seconds=ttl_seconds)
+                params, trial_index = self.get_next_trial(
+                    ttl_seconds=ttl_seconds, fixed_features=fixed_features
+                )
                 trials_dict[trial_index] = params
             except OptimizationComplete as err:
                 logger.info(
@@ -1744,20 +1761,16 @@ def _save_generation_strategy_to_db_if_possible(
             suppress_all_errors=suppress_all_errors,
         )
 
-    def _get_last_completed_trial_index(self) -> int:
-        # infer last completed trial as the trial_index to use
-        # TODO: use Experiment.completed_trials once D46484953 lands.
-        completed_indices = [
-            t.index for t in self.experiment.trials_by_status[TrialStatus.COMPLETED]
-        ]
-        completed_indices.append(0)  # handle case of no completed trials
-        return max(completed_indices)
-
-    def _gen_new_generator_run(self, n: int = 1) -> GeneratorRun:
+    def _gen_new_generator_run(
+        self, n: int = 1, fixed_features: Optional[FixedFeatures] = None
+    ) -> GeneratorRun:
         """Generate new generator run for this experiment.
 
         Args:
             n: Number of arms to generate.
+            fixed_features: A FixedFeatures object containing any
+                features that should be fixed at specified values during
+                generation.
         """
         # If random seed is not set for this optimization, context manager does
         # nothing; otherwise, it sets the random seed for torch, but only for the
@@ -1767,10 +1780,8 @@ def _gen_new_generator_run(self, n: int = 1) -> GeneratorRun:
         # stochasticity.
 
         fixed_feats = InstantiationBase.make_fixed_observation_features(
-            fixed_features=FixedFeatures(
-                parameters={}, trial_index=self._get_last_completed_trial_index()
-            )
-        )
+            fixed_features=fixed_features
+        ) if fixed_features else None
         with manual_seed(seed=self._random_seed):
             return not_none(self.generation_strategy).gen(
                 experiment=self.experiment,

ax/service/tests/test_ax_client.py

@@ -65,6 +65,7 @@
     observed_pareto,
     predicted_pareto,
 )
+from ax.service.utils.instantiation import FixedFeatures
 from ax.storage.sqa_store.db import init_test_engine_and_session_factory
 from ax.storage.sqa_store.decoder import Decoder
 from ax.storage.sqa_store.encoder import Encoder
@@ -2847,11 +2848,19 @@ def test_gen_fixed_features(self) -> None:
         with mock.patch.object(
             GenerationStrategy, "gen", wraps=ax_client.generation_strategy.gen
         ) as mock_gen:
-            params, idx = ax_client.get_next_trial()
-            call_kwargs = mock_gen.call_args_list[0][1]
-            ff = call_kwargs["fixed_features"]
-            self.assertEqual(ff.parameters, {})
-            self.assertEqual(ff.trial_index, 0)
+            with self.subTest("fixed_features is None"):
+                params, idx = ax_client.get_next_trial()
+                call_kwargs = mock_gen.call_args_list[0][1]
+                ff = call_kwargs["fixed_features"]
+                self.assertEqual(ff.parameters, {})
+                self.assertEqual(ff.trial_index, 0)
+            with self.subTest("fixed_features is set"):
+                fixed_features = FixedFeatures(parameters={"x": 0.0, "y": 5.0})
+                params, idx = ax_client.get_next_trial(fixed_features=fixed_features)
+                call_kwargs = mock_gen.call_args_list[1][1]
+                ff = call_kwargs["fixed_features"]
+                self.assertEqual(ff.parameters, fixed_features.parameters)
+                self.assertEqual(ff.trial_index, 0)
 
     def test_get_optimization_trace_discard_infeasible_trials(self) -> None:
         ax_client = AxClient()