pierrejeambrun commented on code in PR #45062:
URL: https://github.com/apache/airflow/pull/45062#discussion_r1904194885


##########
airflow/models/backfill.py:
##########
@@ -47,13 +38,15 @@
 from airflow.settings import json
 from airflow.utils import timezone
 from airflow.utils.session import create_session
-from airflow.utils.sqlalchemy import UtcDateTime, nulls_first, with_row_locks
+from airflow.utils.sqlalchemy import UtcDateTime, with_row_locks
 from airflow.utils.state import DagRunState
 from airflow.utils.types import DagRunTriggeredByType, DagRunType
 
 if TYPE_CHECKING:
     from datetime import datetime
 
+    from typing_extensions import Literal

Review Comment:
   Import Literal from `typing`



##########
airflow/models/backfill.py:
##########
@@ -158,72 +151,125 @@ def validate_sort_ordinal(self, key, val):
 def _create_backfill_dag_run(
     *,
     dag,
-    info,
-    reprocess_behavior: ReprocessBehavior,
+    dagrun_info_list,
+    reprocess_behavior: ReprocessBehavior | None = None,
     backfill_id,
-    dag_run_conf,
-    backfill_sort_ordinal,
+    dag_run_conf: dict | None,
     session,
-):
+    dry_run,
+) -> list[datetime]:
     from airflow.models import DagRun
 
-    with session.begin_nested() as nested:
-        dr = session.scalar(
-            with_row_locks(
-                select(DagRun)
-                .where(DagRun.logical_date == info.logical_date)
-                .order_by(nulls_first(desc(DagRun.start_date), 
session=session))
-                .limit(1),
-                session=session,
+    backfill_sort_ordinal = 0
+    logical_dates = []
+    dagrun_infos = list(dagrun_info_list)
+
+    if reprocess_behavior is None:
+        reprocess_behavior = ReprocessBehavior.NONE
+    if dag_run_conf is None:
+        dag_run_conf = {}
+
+    dag_run_ranked = (
+        select(
+            DagRun.logical_date,
+            DagRun.start_date,
+            DagRun.dag_id,
+            func.row_number()
+            .over(
+                partition_by=DagRun.logical_date,
+                order_by=(case([(DagRun.start_date.is_(None), 0)], else_=1), 
DagRun.start_date.desc()),
             )
+            .label("row_number"),
         )
-        if dr:
-            non_create_reason = None
-            if dr.state not in (DagRunState.SUCCESS, DagRunState.FAILED):
-                non_create_reason = BackfillDagRunExceptionReason.IN_FLIGHT
-            elif reprocess_behavior is ReprocessBehavior.NONE:
-                non_create_reason = 
BackfillDagRunExceptionReason.ALREADY_EXISTS
-            elif reprocess_behavior is ReprocessBehavior.FAILED:
-                if dr.state != DagRunState.FAILED:
+        .where(DagRun.dag_id == dag.dag_id)
+        .where(DagRun.logical_date.in_([info.logical_date for info in 
dagrun_infos]))
+        .subquery()
+    )
+
+    existing_dag_runs = {
+        dr.logical_date: dr
+        for dr in session.scalars(
+            select(DagRun)
+            .join(
+                dag_run_ranked,
+                (DagRun.logical_date == dag_run_ranked.c.logical_date)
+                & (
+                    (DagRun.start_date == dag_run_ranked.c.start_date)
+                    | ((DagRun.start_date.is_(None)) & 
(dag_run_ranked.c.start_date.is_(None)))
+                )
+                & (DagRun.dag_id == dag_run_ranked.c.dag_id),
+            )
+            .where(dag_run_ranked.c.row_number == 1)
+        ).all()
+    }
+
+    print(existing_dag_runs)

Review Comment:
   to remove `print` statements



##########
airflow/models/backfill.py:
##########
@@ -158,72 +151,125 @@ def validate_sort_ordinal(self, key, val):
 def _create_backfill_dag_run(
     *,
     dag,
-    info,
-    reprocess_behavior: ReprocessBehavior,
+    dagrun_info_list,
+    reprocess_behavior: ReprocessBehavior | None = None,
     backfill_id,
-    dag_run_conf,
-    backfill_sort_ordinal,
+    dag_run_conf: dict | None,
     session,
-):
+    dry_run,
+) -> list[datetime]:
     from airflow.models import DagRun
 
-    with session.begin_nested() as nested:
-        dr = session.scalar(
-            with_row_locks(
-                select(DagRun)
-                .where(DagRun.logical_date == info.logical_date)
-                .order_by(nulls_first(desc(DagRun.start_date), 
session=session))
-                .limit(1),
-                session=session,
+    backfill_sort_ordinal = 0
+    logical_dates = []
+    dagrun_infos = list(dagrun_info_list)

Review Comment:
   I think we need to slightly modify `_get_info_list` to not have to 
explicitely cast to dict. Also we can add types. ( -> list[DagRunInfo])



##########
airflow/models/backfill.py:
##########
@@ -158,72 +151,125 @@ def validate_sort_ordinal(self, key, val):
 def _create_backfill_dag_run(
     *,
     dag,
-    info,
-    reprocess_behavior: ReprocessBehavior,
+    dagrun_info_list,
+    reprocess_behavior: ReprocessBehavior | None = None,
     backfill_id,
-    dag_run_conf,
-    backfill_sort_ordinal,
+    dag_run_conf: dict | None,
     session,
-):
+    dry_run,
+) -> list[datetime]:
     from airflow.models import DagRun
 
-    with session.begin_nested() as nested:
-        dr = session.scalar(
-            with_row_locks(
-                select(DagRun)
-                .where(DagRun.logical_date == info.logical_date)
-                .order_by(nulls_first(desc(DagRun.start_date), 
session=session))
-                .limit(1),
-                session=session,
+    backfill_sort_ordinal = 0
+    logical_dates = []
+    dagrun_infos = list(dagrun_info_list)
+
+    if reprocess_behavior is None:
+        reprocess_behavior = ReprocessBehavior.NONE
+    if dag_run_conf is None:
+        dag_run_conf = {}
+
+    dag_run_ranked = (
+        select(
+            DagRun.logical_date,
+            DagRun.start_date,
+            DagRun.dag_id,
+            func.row_number()
+            .over(
+                partition_by=DagRun.logical_date,
+                order_by=(case([(DagRun.start_date.is_(None), 0)], else_=1), 
DagRun.start_date.desc()),
             )
+            .label("row_number"),
         )
-        if dr:
-            non_create_reason = None
-            if dr.state not in (DagRunState.SUCCESS, DagRunState.FAILED):
-                non_create_reason = BackfillDagRunExceptionReason.IN_FLIGHT
-            elif reprocess_behavior is ReprocessBehavior.NONE:
-                non_create_reason = 
BackfillDagRunExceptionReason.ALREADY_EXISTS
-            elif reprocess_behavior is ReprocessBehavior.FAILED:
-                if dr.state != DagRunState.FAILED:
+        .where(DagRun.dag_id == dag.dag_id)
+        .where(DagRun.logical_date.in_([info.logical_date for info in 
dagrun_infos]))
+        .subquery()
+    )
+
+    existing_dag_runs = {
+        dr.logical_date: dr
+        for dr in session.scalars(
+            select(DagRun)
+            .join(
+                dag_run_ranked,
+                (DagRun.logical_date == dag_run_ranked.c.logical_date)
+                & (
+                    (DagRun.start_date == dag_run_ranked.c.start_date)
+                    | ((DagRun.start_date.is_(None)) & 
(dag_run_ranked.c.start_date.is_(None)))
+                )
+                & (DagRun.dag_id == dag_run_ranked.c.dag_id),
+            )
+            .where(dag_run_ranked.c.row_number == 1)
+        ).all()
+    }

Review Comment:
   I assume all that is necessary because of the removal of the unique 
constraint on the `logical_date` ?
   
   What are the update on that ?
   
   cc: @dstandish 



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