seanmuth opened a new issue, #73686:
URL: https://github.com/apache/airflow/issues/73686
Today, when a Dag is at `max_active_runs`, there is very little signal
anywhere that explains it, across three different surfaces:
- **Logs**: the only existing log message covering this lives in the
scheduler's periodic bookkeeping (`_set_exceeds_max_active_runs`), and as of
#72403 it includes the blocking run/task IDs — but only at the moment a Dag
*newly* becomes blocked. A Dag Run created *after* the Dag is already at
capacity (e.g. a second manual trigger while the first run is still active)
produces no log output anywhere explaining why it never starts.
- **API**: `DagModel.exceeds_max_non_backfill` (added in 3.2.0 by migration
`0099_3_2_0_add_exceeds_max_runs_flag_to_dag_model`) is persisted to the `dag`
table but is never exposed on `DAGResponse` (`GET /dags/{dag_id}`) or anywhere
else in the public API. There is no way for a client to ask "is this Dag
currently blocked on max_active_runs" without independently computing
active-run counts.
- **UI**: the Dag header's "Active Runs" stat
(`airflow-core/src/airflow/ui/src/pages/Dag/Header.tsx`) shows `X of Y` (e.g.
"2 of 1") once a Dag is at or over its limit, but nothing explains what that
means or what happens to the extra run. An info/warning icon with a tooltip
explaining that a newly-created run will not start until an existing active run
completes would make this self-explanatory without needing to dig through
scheduler logs at all.
Related: #72387 / #72403 — that work enhances the "Dag newly became blocked"
log message with blocking run/task IDs. It is complementary to, not overlapping
with, the gaps above (different trigger point, different code path).
### Proposed follow-up work
One PR per item, so each can be reviewed independently:
1. Log when a newly-created Dag Run will not be scheduled yet because the
Dag is already at `max_active_runs` (covers the manual-trigger-while-blocked
case that #72403 does not).
2. Expose `exceeds_max_non_backfill` (or an equivalently named field) on
`DAGResponse`.
3. Add an info/warning tooltip next to the "Active Runs" stat in the Dag
header UI explaining the blocking behavior.
---
Drafted-by: Claude Sonnet 5 (no human review before posting)
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