Add metrics for how often a dag gets serialised.

airflow-core/src/airflow/models/serialized_dag.py

@@ -32,6 +32,7 @@
 from sqlalchemy.orm import Mapped, backref, foreign, mapped_column, relationship
 from sqlalchemy.sql.expression import func, literal
 
+from airflow._shared.observability.metrics import stats
 from airflow._shared.timezones import timezone
 from airflow.configuration import conf
 from airflow.models.asset import (
@@ -762,6 +763,7 @@ def write_dag(
             session.merge(dag_version)
             # Update the latest DagCode
             DagCode.update_source_code(dag_id=dag.dag_id, fileloc=dag.fileloc, session=session)
+            stats.incr("dag.serialization", tags={"dag_id": dag.dag_id, "bundle_name": bundle_name})
             return True
 
         dagv = DagVersion.write_dag(
@@ -777,6 +779,7 @@ def write_dag(
         cls._create_deadline_alert_records(new_serialized_dag, deadline_uuid_mapping)
         log.debug("DAG: %s written to the DB", dag.dag_id)
         DagCode.write_code(dagv, dag.fileloc, session=session)
+        stats.incr("dag.serialization", tags={"dag_id": dag.dag_id, "bundle_name": bundle_name})
         return True
 
     @classmethod

airflow-core/tests/unit/models/test_serialized_dag.py

@@ -28,6 +28,7 @@
 from sqlalchemy import delete, func, select, update
 
 import airflow.example_dags as example_dags_module
+from airflow._shared.observability.metrics.base_stats_logger import StatsLogger
 from airflow.dag_processing.dagbag import DagBag
 from airflow.models.asset import AssetActive, AssetAliasModel, AssetModel
 from airflow.models.dag import DagModel
@@ -90,6 +91,8 @@ def make_example_dags(module):
 class TestSerializedDagModel:
     """Unit tests for SerializedDagModel."""
 
+    SERIALIZED_DAG_STATS = "airflow.models.serialized_dag.stats"
+
     @pytest.fixture(
         autouse=True,
         params=[
@@ -201,6 +204,76 @@ def test_serialized_dag_is_updated_if_dag_is_changed(self, testing_dag_bundle):
         assert s_dag_2.data["dag"]["tags"] == ["example", "new_tag", "params"]
         assert dag_updated is True
 
+    def test_serialization_metric_incremented_on_new_write(self, testing_dag_bundle):
+        """A brand new serialized DAG write emits the ``dag.serialization`` metric."""
+        dag = make_example_dags(example_dags_module).get("example_params_trigger_ui")
+        with mock.patch(self.SERIALIZED_DAG_STATS) as mock_stats:
+            assert SDM.write_dag(LazyDeserializedDAG.from_dag(dag), bundle_name="testing") is True
+
+        mock_stats.incr.assert_called_once_with(
+            "dag.serialization",
+            tags={"dag_id": dag.dag_id, "bundle_name": "testing"},
+        )
+
+    def test_serialization_metric_not_incremented_when_unchanged(self, testing_dag_bundle):
+        """Re-writing an unchanged DAG must not emit the ``dag.serialization`` metric."""
+        dag = make_example_dags(example_dags_module).get("example_params_trigger_ui")
+        assert SDM.write_dag(LazyDeserializedDAG.from_dag(dag), bundle_name="testing") is True
+
+        with mock.patch(self.SERIALIZED_DAG_STATS) as mock_stats:
+            assert SDM.write_dag(LazyDeserializedDAG.from_dag(dag), bundle_name="testing") is False
+
+        mock_stats.incr.assert_not_called()
+
+    def test_serialization_metric_incremented_on_inplace_update(self, dag_maker, session):
+        """Updating a DAG version in place (no dag runs) emits the metric once."""
+        with dag_maker("metric_dag") as dag:
+            PythonOperator(task_id="task1", python_callable=lambda: None)
+        # Change the DAG so the hash differs; with no dag runs this updates in place.
+        PythonOperator(task_id="task2", python_callable=lambda: None, dag=dag)
+
+        with mock.patch(self.SERIALIZED_DAG_STATS) as mock_stats:
+            assert SDM.write_dag(LazyDeserializedDAG.from_dag(dag), bundle_name="dag_maker") is True
+
+        assert session.scalar(select(func.count()).select_from(DagVersion)) == 1
+        mock_stats.incr.assert_called_once_with(
+            "dag.serialization",
+            tags={"dag_id": "metric_dag", "bundle_name": "dag_maker"},
+        )
+
+    def test_serialization_metric_incremented_on_new_version(self, dag_maker, session):
+        """Writing a new DAG version (existing run) emits the metric once."""
+        with dag_maker("metric_dag") as dag:
+            PythonOperator(task_id="task1", python_callable=lambda: None)
+        dag_maker.create_dagrun(run_id="run1", logical_date=pendulum.datetime(2025, 1, 1))
+        PythonOperator(task_id="task2", python_callable=lambda: None, dag=dag)
+
+        with mock.patch(self.SERIALIZED_DAG_STATS) as mock_stats:
+            assert SDM.write_dag(LazyDeserializedDAG.from_dag(dag), bundle_name="dag_maker") is True
+
+        assert session.scalar(select(func.count()).select_from(DagVersion)) == 2
+        mock_stats.incr.assert_called_once_with(
+            "dag.serialization",
+            tags={"dag_id": "metric_dag", "bundle_name": "dag_maker"},
+        )
+
+    @mock.patch("airflow._shared.observability.metrics.stats._export_legacy_names", True)
+    @mock.patch("airflow._shared.observability.metrics.stats._get_backend")
+    def test_serialization_metric_exports_new_and_legacy_names(self, mock_get_backend, testing_dag_bundle):
+        """Serializing a DAG emits both the modern ``dag.serialization`` metric and its legacy name."""
+        mock_backend = mock.MagicMock(spec=StatsLogger)
+        mock_get_backend.return_value = mock_backend
+        dag = make_example_dags(example_dags_module).get("example_params_trigger_ui")
+
+        assert SDM.write_dag(LazyDeserializedDAG.from_dag(dag), bundle_name="testing") is True
+
+        mock_backend.incr.assert_has_calls(
+            [
+                mock.call(f"dag.serialization.{dag.dag_id}.testing"),
+                mock.call("dag.serialization", tags={"dag_id": dag.dag_id, "bundle_name": "testing"}),
+            ]
+        )
+
     def test_read_dags(self):
         """DAGs can be read from database."""
         example_dags = self._write_example_dags()

shared/observability/src/airflow_shared/observability/metrics/metrics_template.yaml

@@ -226,6 +226,13 @@ metrics:
     legacy_name: "-"
     name_variables: []
 
+  - name: "dag.serialization"
+    description: "Number of times a Dag was serialized and written to the metadata DB.
+    Metric with dag_id and bundle_name tagging."
+    type: "counter"
+    legacy_name: "dag.serialization.{dag_id}.{bundle_name}"
+    name_variables: ["dag_id", "bundle_name"]
+
   - name: "celery.task_timeout_error"
     description: "Number of ``AirflowTaskTimeout`` errors raised when publishing Task to Celery Broker."
     type: "counter"