kevinhongzl opened a new pull request, #62294:
URL: https://github.com/apache/airflow/pull/62294
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closes: #62027
### Why this change
This pull request aims to enhance the performance of the
`get_task_instances` endpoint, which can be slow with many task records.
### Proposed solutions
1. Simplify the query
- Reduce the number of JOIN clauses
- Include only columns in TaskInstanceResponse to speed up JOINs
- Use `selectinload` instead of `joinedload` to avoid record duplication
2. Defer joins
- Paginate data before applying joins
- Skip filters that don't affect the query
### Benchmark results
Below are the average times for `get_task_instance` across 5 runs:
| Tests | original | method 1 | method 1 + 2 |
|---|---|---|---|
| PostgreSQL (~24 million rows) | 53.2s | 43.2s (-18.8%) | 21.8s (-59.0%) |
| MySQL (~2 million rows) | 37.0s | 16.8s (-54.6%) | 6.8s (-81.6%) |
### Additional notes
My optimization is based on the default sorting order:
```sql
ORDER BY task_instance.start_date DESC, dag_run.run_after DESC,
task_instance.id DESC
```
Since these columns come from different tables, adding indexes provided only
marginal benefits. I've tried using indexes, but `using temporary` and `using
filesort` still occurred during MySQL tests, and the improvement was
insignificant.
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