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Airflow & DAGs · Core Concepts & DAGs

What are Sensors?

Easyairflow-06
sensorsdeferrable

Question

What are Sensors in Airflow? Give examples.

Solution

Sensors are special tasks that wait for something to happen: a file to land, another DAG to finish, or an external job to complete.

Examples

Wait for sales.csv → Process file
Wait for upstream DAG → Start this DAG
Wait for S3/GCS object → Process data

Production tip

Older-style sensors can sit on a worker slot the whole time they're waiting. Deferrable sensors/operators wait through the Triggerer instead, so they don't hog a worker for hours.

Interview tip: Sensor = wait until condition; prefer deferrable sensors for long waits.

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