Hparams: Support limit for DataProvider.list_hyperparameters(). (#6569)

Support `limit` for `DataProvider.list_hyperparameters()`. Note that
this PR does not support limiting the hparams returned from
`DataProvider.list_tensors()`.

Googlers, see cl/559192614 and cl/563165193 for more context.

#hparams

Author: yatbear

tensorboard/data/provider.py

@@ -379,13 +379,15 @@ def read_blob(self, ctx=None, *, blob_key):
         """
         pass
 
-    def list_hyperparameters(self, ctx=None, *, experiment_ids):
+    def list_hyperparameters(self, ctx=None, *, experiment_ids, limit=None):
         """List hyperparameters metadata.
 
         Args:
           ctx: A TensorBoard `RequestContext` value.
           experiment_ids: A Collection[string] of IDs of the enclosing
             experiments.
+          limit: Optional number of hyperparameter metadata to include in the
+            result. If unset or zero, all metadata will be included.
 
         Returns:
           A ListHyperparametersResult describing the hyperparameter-related

tensorboard/plugins/hparams/api.proto

@@ -254,13 +254,17 @@ enum Status {
 
 // Parameters for a GetExperiment API call.
 // Each experiment is scoped by a unique global id.
-// NEXT_TAG: 3
+// NEXT_TAG: 4
 message GetExperimentRequest {
   // REQUIRED
   string experiment_name = 1;
 
   // Whether to fetch metrics and include them in the results. Defaults to true.
   optional bool include_metrics = 2;
+
+  // Number of hyperparameter metadata to include in the result. If zero, all
+  // hyperparameter metadata will be returned.
+  optional int32 hparams_limit = 3;
 }
 
 // Parameters for a ListSessionGroups API call.

tensorboard/plugins/hparams/backend_context.py

@@ -193,10 +193,10 @@ def read_last_scalars(self, ctx, experiment_id, run_tag_filter):
             for (run, tag_to_data) in data_provider_output.items()
         }
 
-    def hparams_from_data_provider(self, ctx, experiment_id):
+    def hparams_from_data_provider(self, ctx, experiment_id, limit):
         """Calls DataProvider.list_hyperparameters() and returns the result."""
         return self._tb_context.data_provider.list_hyperparameters(
-            ctx, experiment_ids=[experiment_id]
+            ctx, experiment_ids=[experiment_id], limit=limit
         )
 
     def session_groups_from_data_provider(

tensorboard/plugins/hparams/backend_context_test.py

@@ -149,6 +149,7 @@ def _mock_list_hyperparameters(
         ctx,
         *,
         experiment_ids,
+        limit,
     ):
         return self._hyperparameters
 
@@ -161,7 +162,7 @@ def _experiment_from_metadata(self, *, include_metrics=True):
             "123",
             include_metrics,
             ctxt.hparams_metadata(request_ctx, "123"),
-            ctxt.hparams_from_data_provider(request_ctx, "123"),
+            ctxt.hparams_from_data_provider(request_ctx, "123", limit=None),
         )
 
     def test_experiment_with_experiment_tag(self):

tensorboard/plugins/hparams/get_experiment.py

@@ -38,6 +38,7 @@ def __init__(
             not request.HasField("include_metrics")
             or request.include_metrics
         )
+        self._hparams_limit = request.hparams_limit
 
     def run(self):
         """Handles the request specified on construction.
@@ -53,6 +54,8 @@ def run(self):
                 self._request_context, self._experiment_id
             ),
             self._backend_context.hparams_from_data_provider(
-                self._request_context, self._experiment_id
+                self._request_context,
+                self._experiment_id,
+                limit=self._hparams_limit,
             ),
         )