vatsrahul1001 opened a new issue, #63532:
URL: https://github.com/apache/airflow/issues/63532
### Apache Airflow version
main (development)
### If "Other Airflow 3 version" selected, which one?
_No response_
### What happened?
Migration 0094_3_2_0_replace_deadline_inline_callback_with_fkey processes
every row in the deadline table through Python's serde.deserialize() during
upgrade. For each row it deserializes the JSON callback, instantiates the
Python object, re-serializes it into the new format, then writes to the
callback table.
With a large number of deadline rows this becomes very slow because the
bottleneck is Python-side object instantiation — not the database I/O. The
migration processes rows in batches of 1000, but within each batch every row
goes through:
```
callback_data = deserialize(deadline.callback).serialize() | {
"prefix": CALLBACK_METRICS_PREFIX,
"dag_id": deadline.dag_id,
}
```
This round-trip through Python deserialization/serialization is unnecessary
given that the callback JSON format is predictable. Prior to 3.2.0 the only
supported callback type was AsyncCallback, which has a fixed structure
```
{
"__data__": {"path": "...", "kwargs": {...}},
"__classname__": "airflow.sdk.definitions.deadline.AsyncCallback",
"__version__": 0
}
```
The transformation could be done entirely in SQL by extracting path and
kwargs from the existing JSON and constructing the new callback row format
without ever touching Python.
Observed impact:
10M deadline rows: ~33 minutes
The migration holds a transaction open for the entire duration
Proportional to deadline row count — 1M rows would still take ~3 minutes
### What you think should happen instead?
_No response_
### How to reproduce
**Steps to reproduce:**
1. Start Airflow 3.1.8 with PostgreSQL backend
2. Create a significant number of DAG runs with deadlines (or insert
synthetic data into the deadline table with valid serde-formatted callback JSON)
3. Upgrade to 3.2.0 (airflow db migrate)
4. Observe that migration 0094 takes several minutes per million deadline
rows
### Operating System
Mac
### Versions of Apache Airflow Providers
_No response_
### Deployment
Official Apache Airflow Helm Chart
### Deployment details
_No response_
### Anything else?
_No response_
### Are you willing to submit PR?
- [ ] Yes I am willing to submit a PR!
### Code of Conduct
- [x] I agree to follow this project's [Code of
Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)
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