uranusjr commented on code in PR #71072:
URL: https://github.com/apache/airflow/pull/71072#discussion_r3732967216


##########
airflow-core/src/airflow/jobs/scheduler_job_runner.py:
##########
@@ -2247,13 +2256,55 @@ def _create_dagruns_for_partitioned_asset_dags(self, 
session: Session) -> set[st
                     DagModel.is_stale.is_(False),
                 )
                 .order_by(AssetPartitionDagRun.created_at, 
AssetPartitionDagRun.id)
-                .limit(self._max_partition_dag_runs_per_loop),
+                .limit(self._max_partition_dag_runs_per_loop + 1),
                 of=AssetPartitionDagRun,
                 skip_locked=True,
                 key_share=False,
                 session=session,
             )
         ).all()
+        has_backlog = len(rows) > self._max_partition_dag_runs_per_loop
+        pending_apdrs = rows[: self._max_partition_dag_runs_per_loop]
+        if has_backlog:
+            self.log.warning(
+                "Reached the per-tick cap on pending partitioned Dag runs; the 
remaining backlog "
+                "will be evaluated over subsequent scheduler ticks",
+                cap=self._max_partition_dag_runs_per_loop,
+                pending_count=len(pending_apdrs),

Review Comment:
   The cap+1 approach may have other issues with HA since we’re locking one 
more row that does not belong to this process. Since we need a separate count 
anyway, maybe something like this would be better:
   
   ```python
   # No +1 in the limit!
   pending_apdrs = session.scalars(with_row_locks(... .limit(cap), ...)).all()
   
   if len(pending_apdrs) >= self._max_partition_dag_runs_per_loop:
       backlog_total = session.scalar(count_query)
       has_backlog = backlog_total > self._max_partition_dag_runs_per_loop
   ```
   
   Also, if row count if a problem, we should add an index on APDR to prevent 
table scan.



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