potiuk commented on issue #56723:
URL: https://github.com/apache/airflow/issues/56723#issuecomment-3418703943
> This should be the expected behavior right ?
Sounds about right. "always" means that that B, C and `start` should start
together. "always" applies to all upstream dependencies of those tasks (both
"start" and "A").
As @ashb wrote - we do not have the notion of "task group" upstream task -
so if B and C have "always" - they will start immediately, without waiting for
anything, there is nothing like "starting a task group".
I guess that (if interpret correctly the use case here) - If we would like
to wait with starting B, C until "start" completes, but not for A, then the
right dependency should be:
start -> ["A", "B", "C", "E"] (with default trigger types)
Then "start" becomes effectively "task group" prerequisite (because it is
prerequisite of all tasks that are "entry" nodes for the task group.
Another way of modelling "tg" dependency in this case would be to have a
separate "0" Empty task (kind of single entry-point for the task group).
```
"start" >> "0"
"0" >> {"A", "B", "C"}
"A" >> "E"
"C" >> "D"
"E" >> "F"
```
In the model where A, B, C can all start together, they are effectively at
the same "up/down" stream place in Dag.
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