Repository: apache/airflow

Issue:
Fix lost runs in `CronTriggerTimetable`
closes: #27399

Fix lost runs in `CronTriggerTimetable` by resetting seconds and microseconds in `start_time_candidates`.
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Discussion:
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I think it also fixes #31687 which is essentially a duplicate of #27399.

@uranusjr WDYT?

Resolving patch:
diff --git a/airflow/timetables/trigger.py b/airflow/timetables/trigger.py
--- a/airflow/timetables/trigger.py
+++ b/airflow/timetables/trigger.py
@@ -89,7 +89,7 @@ def next_dagrun_info(
             else:
                 next_start_time = self._align_to_next(restriction.earliest)
         else:
-            start_time_candidates = [self._align_to_next(DateTime.utcnow())]
+            start_time_candidates = [self._align_to_prev(DateTime.utcnow())]
             if last_automated_data_interval is not None:
                 start_time_candidates.append(self._get_next(last_automated_data_interval.end))
             if restriction.earliest is not None:


Test patch:
diff --git a/tests/timetables/test_trigger_timetable.py b/tests/timetables/test_trigger_timetable.py
--- a/tests/timetables/test_trigger_timetable.py
+++ b/tests/timetables/test_trigger_timetable.py
@@ -48,11 +48,11 @@
     [
         pytest.param(
             None,
-            CURRENT_TIME + DELTA_FROM_MIDNIGHT,
+            YESTERDAY + DELTA_FROM_MIDNIGHT,
             id="first-run",
         ),
         pytest.param(
-            PREV_DATA_INTERVAL_EXACT,
+            DataInterval.exact(YESTERDAY + DELTA_FROM_MIDNIGHT),
             CURRENT_TIME + DELTA_FROM_MIDNIGHT,
             id="before-now",
         ),
@@ -89,9 +89,21 @@ def test_daily_cron_trigger_no_catchup_first_starts_at_next_schedule(
         pytest.param(
             pendulum.DateTime(2022, 7, 27, 0, 30, 0, tzinfo=TIMEZONE),
             START_DATE,
-            DagRunInfo.exact(pendulum.DateTime(2022, 7, 27, 1, 0, 0, tzinfo=TIMEZONE)),
+            DagRunInfo.exact(pendulum.DateTime(2022, 7, 27, 0, 0, 0, tzinfo=TIMEZONE)),
             id="current_time_not_on_boundary",
         ),
+        pytest.param(
+            pendulum.DateTime(2022, 7, 27, 1, 0, 0, tzinfo=TIMEZONE),
+            START_DATE,
+            DagRunInfo.exact(pendulum.DateTime(2022, 7, 27, 1, 0, 0, tzinfo=TIMEZONE)),
+            id="current_time_miss_one_interval_on_boundary",
+        ),
+        pytest.param(
+            pendulum.DateTime(2022, 7, 27, 1, 30, 0, tzinfo=TIMEZONE),
+            START_DATE,
+            DagRunInfo.exact(pendulum.DateTime(2022, 7, 27, 1, 0, 0, tzinfo=TIMEZONE)),
+            id="current_time_miss_one_interval_not_on_boundary",
+        ),
         pytest.param(
             pendulum.DateTime(2022, 7, 27, 0, 30, 0, tzinfo=TIMEZONE),
             pendulum.DateTime(2199, 12, 31, 22, 30, 0, tzinfo=TIMEZONE),