PostgresToGCSOperator server-side cursor ignores cursor_itersize with psycopg3 driver (FETCH FORWARD 1)

[eric-workweek]

Description

When using PostgresToGCSOperator with use_server_side_cursor=True and cursor_itersize=10000, the operator issues FETCH FORWARD 1 per row instead of batching when the psycopg3 driver is active (providers-postgres >= 7.0.0).

The _PostgresServerSideCursorDecorator uses fetchone() for the psycopg3 code path, which bypasses the cursor's itersize attribute entirely. With psycopg2 it iterated over the cursor (which respects itersize).

Impact

A 2M row table went from ~5 min to 90+ min (17x slower). The operator becomes unusable for large tables with the psycopg3 driver.

Steps to Reproduce

1. Use apache-airflow-providers-postgres>=7.0.0 (psycopg3 default)
2. Configure PostgresToGCSOperator with use_server_side_cursor=True, cursor_itersize=10000
3. Run against a table with >100k rows
4. Observe pg_stat_activity shows FETCH FORWARD 1 instead of FETCH FORWARD 10000

Expected Behavior

Server-side cursor should fetch in batches of cursor_itersize (e.g. FETCH FORWARD 10000).

Environment

• Airflow 3.3.1
• apache-airflow-providers-google 22.1.0
• apache-airflow-providers-postgres 7.0.0+ (bug present)
• Astro Runtime 3.3.5

Workaround

Pin apache-airflow-providers-postgres<7.0.0 to stay on psycopg2.

[dhruv0703]

Hi, I'd like to work on this. I'll reproduce the psycopg3 server-side cursor behavior and look into updating the fetch logic to respect cursor_itersize, along with the relevant tests.