vatsrahul1001 opened a new issue, #75007:
URL: https://github.com/apache/airflow/issues/75007
### Apache Airflow version
3.4.0b1 (v3-4-test)
### What happened
An asset-triggered timetable deserializes `batch_asset_events` to **`True`**
when the key is absent from the serialized data, but the authoring/config
default is **`False`** (asset-event batching is opt-in, added in #68517). So
any serialized DAG whose blob lacks the key — every DAG serialized before 3.4,
and the transient window after upgrade before the dag-processor re-parses —
comes back with `batch_asset_events=True`, silently batching queued asset
events into a single DAG run instead of one run per event.
The three deserialize sites all hardcode the `True` fallback:
- `airflow-core/src/airflow/timetables/simple.py:251`
(`AssetTriggeredTimetable`)
- `airflow-core/src/airflow/timetables/simple.py:465`
(`PartitionedAssetTimetable`)
- `airflow-core/src/airflow/timetables/assets.py:71` (`AssetOrTimeSchedule`)
whereas the attrs field default is
`attrs.Factory(_get_default_batch_asset_events)` which returns
`conf.getboolean("scheduler", "batch_asset_events", fallback=False) or
get_batching_requirement() is not None` — i.e. `False` for a plain asset
condition.
### What you think should happen instead
Deserializing a blob without the key should yield the same value as
authoring the timetable — `False` for a plain condition (and `True` for
AND/partition conditions, which *require* batching). I.e. the absent-key
fallback should defer to the construct-time factory default, not a hardcoded
`True`.
### How to reproduce
```python
from airflow.sdk import Asset
from airflow.timetables.simple import AssetTriggeredTimetable
tt = AssetTriggeredTimetable(assets=Asset("x"))
print(tt.batch_asset_events) # False (opt-in default)
legacy_blob = {"asset_condition": tt.serialize()["asset_condition"]} # key
omitted
restored = AssetTriggeredTimetable.deserialize(legacy_blob)
print(restored.batch_asset_events) # True <-- bug
```
Confirmed on v3-4-test. A normal round-trip (`deserialize(tt.serialize())`,
key present) correctly returns `False`.
### Suggested fix
At each deserialize site, only pass `batch_asset_events` when the key is
present so the attrs factory default applies when it is absent. A hardcoded
`False` is **not** correct because AND-condition / partitioned timetables
require batching (`True`).
### Are you willing to submit PR?
Yes.
### Operating System / Deployment / Versions
v3-4-test branch (3.4.0).
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