Two fixes for handling edge cases in MLflow logging (#16451)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

src/pytorch_lightning/CHANGELOG.md

@@ -134,6 +134,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 - Fixed an issue with `MLFlowLogger` logging the wrong keys with `.log_hyperparams()` ([#16418](https://github.com/Lightning-AI/lightning/pull/16418))
 
+- Fixed logging more than 100 parameters with `MLFlowLogger` and long values are truncated ([#16451](https://github.com/Lightning-AI/lightning/pull/16451))
+
 
 
 ## [1.9.0] - 2023-01-17

src/pytorch_lightning/loggers/mlflow.py

@@ -238,18 +238,14 @@ class MLFlowLogger(Logger):
     def log_hyperparams(self, params: Union[Dict[str, Any], Namespace]) -> None:
         params = _convert_params(params)
         params = _flatten_dict(params)
-        params_list: List[Param] = []
 
-        for k, v in params.items():
-            # TODO: mlflow 1.28 allows up to 500 characters: https://github.com/mlflow/mlflow/releases/tag/v1.28.0
-            if len(str(v)) > 250:
-                rank_zero_warn(
-                    f"Mlflow only allows parameters with up to 250 characters. Discard {k}={v}", category=RuntimeWarning
-                )
-                continue
-            params_list.append(Param(key=k, value=v))
+        # 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()]
 
-        self.experiment.log_batch(run_id=self.run_id, params=params_list)
+        # Log in chunks of 100 parameters (the maximum allowed by MLflow).
+        for idx in range(0, len(params_list), 100):
+            self.experiment.log_batch(run_id=self.run_id, params=params_list[idx : idx + 100])
 
     @rank_zero_only
     def log_metrics(self, metrics: Mapping[str, float], step: Optional[int] = None) -> None:

tests/tests_pytorch/loggers/test_mlflow.py

@@ -224,19 +224,6 @@ def test_mlflow_logger_with_unexpected_characters(client, _, __, tmpdir):
         logger.log_metrics(metrics)
 
 
-@mock.patch("pytorch_lightning.loggers.mlflow._MLFLOW_AVAILABLE", return_value=True)
-@mock.patch("pytorch_lightning.loggers.mlflow.MlflowClient")
-def test_mlflow_logger_with_long_param_value(client, _, tmpdir):
-    """Test that the logger raises warning with special characters not accepted by MLFlow."""
-    logger = MLFlowLogger("test", save_dir=tmpdir)
-    value = "test" * 100
-    key = "test_param"
-    params = {key: value}
-
-    with pytest.warns(RuntimeWarning, match=f"Discard {key}={value}"):
-        logger.log_hyperparams(params)
-
-
 @mock.patch("pytorch_lightning.loggers.mlflow.Metric")
 @mock.patch("pytorch_lightning.loggers.mlflow.Param")
 @mock.patch("pytorch_lightning.loggers.mlflow.time")
@@ -270,6 +257,38 @@ def test_mlflow_logger_experiment_calls(client, _, time, param, metric, tmpdir):
     )
 
 
+def _check_value_length(value, *args, **kwargs):
+    assert len(value) <= 250
+
+
+@mock.patch("pytorch_lightning.loggers.mlflow.Param", side_effect=_check_value_length)
+@mock.patch("pytorch_lightning.loggers.mlflow._MLFLOW_AVAILABLE", return_value=True)
+@mock.patch("pytorch_lightning.loggers.mlflow.MlflowClient")
+def test_mlflow_logger_with_long_param_value(client, _, param, tmpdir):
+    """Test that long parameter values are truncated to 250 characters."""
+    logger = MLFlowLogger("test", save_dir=tmpdir)
+
+    params = {"test": "test_param" * 50}
+    logger.log_hyperparams(params)
+
+    # assert_called_once_with() won't properly check the parameter value.
+    logger.experiment.log_batch.assert_called_once()
+
+
+@mock.patch("pytorch_lightning.loggers.mlflow.Param")
+@mock.patch("pytorch_lightning.loggers.mlflow._MLFLOW_AVAILABLE", return_value=True)
+@mock.patch("pytorch_lightning.loggers.mlflow.MlflowClient")
+def test_mlflow_logger_with_many_params(client, _, param, tmpdir):
+    """Test that the when logging more than 100 parameters, it will be split into batches of at most 100
+    parameters."""
+    logger = MLFlowLogger("test", save_dir=tmpdir)
+
+    params = {f"test_{idx}": f"test_param_{idx}" for idx in range(150)}
+    logger.log_hyperparams(params)
+
+    assert logger.experiment.log_batch.call_count == 2
+
+
 @pytest.mark.parametrize(
     "status,expected",
     [