feat[logger] update mlflow limit for parameters length log

src/lightning/pytorch/loggers/mlflow.py

@@ -232,11 +232,16 @@ def log_hyperparams(self, params: Union[dict[str, Any], Namespace]) -> None:
         params = _convert_params(params)
         params = _flatten_dict(params)
 
+        import mlflow.utils.validation
         from mlflow.entities import Param
 
-        # Truncate parameter values to 250 characters.
-        # TODO: MLflow 1.28 allows up to 500 characters: https://github.com/mlflow/mlflow/releases/tag/v1.28.0
-        params_list = [Param(key=k, value=str(v)[:250]) for k, v in params.items()]
+        try:  # Check maximum param value length is available and use it
+            param_length_limit = mlflow.utils.validation.MAX_PARAM_VAL_LENGTH
+        except Exception:  # Fallback (in case of MAX_PARAM_VAL_LENGTH not available)
+            param_length_limit = 250  # Historical default value
+
+        # Use mlflow default limit or truncate parameter values to 250 characters if limit is not available
+        params_list = [Param(key=k, value=str(v)[:param_length_limit]) for k, v in params.items()]
 
         # Log in chunks of 100 parameters (the maximum allowed by MLflow).
         for idx in range(0, len(params_list), 100):

tests/tests_pytorch/loggers/test_mlflow.py

@@ -252,6 +252,14 @@ def test_mlflow_logger_experiment_calls(mlflow_mock, tmp_path):
     )
     param.assert_called_with(key="test", value="test_param")
 
+    long_params = {"test": "test_param" * 50}
+    logger.log_hyperparams(long_params)
+
+    logger.experiment.log_batch.assert_called_with(
+        run_id=logger.run_id, params=[param(key="test", value="test_param" * 50)]
+    )
+    param.assert_called_with(key="test", value="test_param" * 50)
+
     metrics = {"some_metric": 10}
     logger.log_metrics(metrics)
 
@@ -317,12 +325,7 @@ def test_mlflow_logger_no_synchronous_support(mlflow_mock, tmp_path):
 
 @mock.patch("lightning.pytorch.loggers.mlflow._get_resolve_tags", Mock())
 def test_mlflow_logger_with_long_param_value(mlflow_mock, tmp_path):
-    """Test that long parameter values are truncated to 250 characters."""
-
-    def _check_value_length(value, *args, **kwargs):
-        assert len(value) <= 250
-
-    mlflow_mock.entities.Param.side_effect = _check_value_length
+    """Test that long parameter values are handled correctly."""
 
     logger = MLFlowLogger("test", save_dir=str(tmp_path))