[Data] Handle distributions without sample counts

Signed-off-by: viiccwen <vicwen@apache.org>

Author: viiccwen

python/ray/data/_internal/stats.py

@@ -758,7 +758,7 @@ def _record(
                 if isinstance(value, RuntimeMetricsHistogram):
                     value.export_to(prom_metric, tags)
             elif isinstance(prom_metric, dict) and isinstance(value, dict):
-                if value.get("num_samples", 0) == 0:
+                if value.get("num_samples") == 0:
                     return
                 for statistic, gauge in prom_metric.items():
                     statistic_value = value.get(statistic)

python/ray/data/tests/test_stats.py

@@ -2035,7 +2035,7 @@ def test_stats_actor_exports_distribution_metrics():
 
         actor.update_execution_metrics(
             "dataset_1",
-            [{"max_uss_bytes": {"num_samples": 2, "mean": 200, "max": 300}}],
+            [{"max_uss_bytes": {"mean": 200, "max": 300}}],
             ["MapBatches_1"],
             {},
         )