What is XCom in Airflow and how is it used?

XCom (cross-communication) is a mechanism that lets tasks exchange small amounts of data. A task can push a value into XCom and a downstream task can pull it.

def push_func(**context):
    context['ti'].xcom_push(key='result', value=42)

def pull_func(**context):
    val = context['ti'].xcom_pull(task_ids='push_task', key='result')
    print(f'Received: {val}')

XCom values are stored in the metadata database, so they should be used for small payloads (strings, numbers, short dicts). Passing large dataframes through XCom is an anti-pattern — use a shared storage layer such as S3 or GCS instead.

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