XComs are not designed for large data. Default size limit is 1 MB (configurable, but don’t). Use them for IDs, file paths, dates, small JSON – not DataFrames or images. The Two Ways to Use XComs 1. Implicit XComs via return Any Python function decorated with @task (TaskFlow API) automatically pushes its return value as an XCom.
process(extract()) # XCom passed implicitly xcom in airflow
✅ or ensure upstream dependencies with >> . ❌ Using XComs for many small values across many tasks Each XCom is a DB row. 10 000 tasks × 5 XComs = 50 000 rows – fine. But 100 000 tasks × 10 XComs = 1 million rows – slow. Advanced: XCom Backends Airflow 2.0+ lets you store XComs outside the metadata DB. Useful if you need slightly larger values or lower DB load. XComs are not designed for large data
XCom (short for cross‑communication ) is Airflow’s built‑in mechanism for exchanging small pieces of data between tasks. When used wisely, they unlock powerful patterns. When abused, they break your DAGs. Let’s see how to use them correctly. XComs are key‑value pairs stored in Airflow’s metadata database. A task can push an XCom (write a value under a key), and another task can pull that value (read it). The Two Ways to Use XComs 1
