"Max active runs" in DAG UI overcounts by including queued runs

[roykoand]

Under which category would you file this issue?

Providers

Apache Airflow version

3.2.2

What happened and how to reproduce it?

The "Max active runs" counter in the DAG detail page header (displayed as "X of Y") counts both Running and Queued Dag runs. However, max_active_runs is only enforced by the scheduler against Running runs. This makes the UI misleading — after a backfill, the counter can show a number far exceeding the configured limit (e.g. 12 of 5), even though the scheduler is behaving correctly.

What you think should happen instead?

The counter should show only Running Dag runs matching exactly what the scheduler enforces. A user looking at 3 of 5 should be able to interpret it as "3 slots taken, 2 available" — which is only true if queued runs are excluded.

Operating System

No response

Deployment

None

Apache Airflow Provider(s)

No response

Versions of Apache Airflow Providers

No response

Official Helm Chart version

Not Applicable

Kubernetes Version

No response

Helm Chart configuration

No response

Docker Image customizations

No response

Anything else?

No response

Are you willing to submit PR?

• Yes I am willing to submit a PR!

Code of Conduct

• I agree to follow this project's Code of Conduct

[Vishwaspatel2401]

@roykoand This comes down to two places disagreeing on what counts as "active."

The scheduler only counts RUNNING runs when deciding whether to promote a queued run ([dagrun.py:729], gated against max_active_runs at dagrun.py:768-769). But the UI's counter, built in [get_dag_details], counts Running and Queued runs and shows that as "X of Y" on the DAG details page.

So the scheduler is behaving correctly, it's just the display that's wrong. The fix is to make the UI count only Running runs, same as the scheduler. Opening a PR for this shortly.

[roykoand]

I just checked the original PR - #58332. This seems like an intentional feature, but IMO it's a bit confusing.