jroachgolf84 commented on code in PR #61596:
URL: https://github.com/apache/airflow/pull/61596#discussion_r2842085799
##########
airflow-core/docs/best-practices.rst:
##########
@@ -457,23 +457,32 @@ Bad example:
class CustomTimetable(CronDataIntervalTimetable):
+
def __init__(self, *args, something=Variable.get("something"),
**kwargs):
self._something = something
super().__init__(*args, **kwargs)
+
Good example:
.. code-block:: python
- from airflow.sdk import Variable
from airflow.timetables.interval import CronDataIntervalTimetable
class CustomTimetable(CronDataIntervalTimetable):
+
def __init__(self, *args, something="something", **kwargs):
- self._something = Variable.get(something)
+ self._something = something
super().__init__(*args, **kwargs)
+.. note::
+
+ Timetables are evaluated during DAG parsing. Accessing Airflow Variables,
+ Connections, or the metadata database inside a timetable (including during
+ ``__init__``) can negatively impact DAG parsing performance or cause
failures.
+ Any database or network access should be deferred until task execution
time.
Review Comment:
Replace `deferred until` with `handled during`. "Deferred" implies
asynchronous execution.
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