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Home/Questions/Spark/Big Data/Explain the difference between TriggerDagRunOperator and ExternalTaskSensor in Airflow.

Explain the difference between TriggerDagRunOperator and ExternalTaskSensor in Airflow.

Spark/Big Datahard0.5 min readPremium

**Why it matters**: At scale, design choices directly impact reliability, latency, and cost. Wrong decisions compound across jobs and teams. TriggerDagRunOperator: triggers another DAG as a task; creates a new run of that DAG. ExternalTaskSensor: waits for a task in another DAG...

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Frequency
Low
Asked at 1 company
Category
452
questions in Spark/Big Data
Difficulty Split
88E|81M|283H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
Citi
Key Concepts Tested
airflowoptimizationpartition

Why This Question Matters

This hard-level Spark/Big Data question appears frequently in data engineering interviews at companies like Citi. While less common, it tests deeper understanding that distinguishes strong candidates. Mastering the underlying concepts (airflow, optimization, partition) will help you answer variations of this question confidently.

How to Approach This

This is a senior-level question that tests architectural thinking. Lead with the high-level design, then drill into specifics. Discuss trade-offs explicitly - there is rarely one correct answer. Show awareness of scale, fault tolerance, and operational complexity.

Expert Answer
108 words

Why it matters: At scale, design choices directly impact reliability, latency, and cost. Wrong decisions compound across jobs and teams.

TriggerDagRunOperator: triggers another DAG as a task; creates a new run of that DAG. ExternalTaskSensor: waits for a task in another DAG to complete (polling). Use TriggerDagRun when you need to explicitly start a child DAG. Use ExternalTaskSensor when your DAG depends on completion of another DAG's task (e.g., wait for upstream pipeline). Best practice: ExternalTaskSensor for cross-DAG dependencies; TriggerDagRun for parent-child orchestration; set execution_delta to match schedules.

Scalability trade-offs: Partition/parallelism limits; single points of failure; horizontal vs vertical scaling. Cost implications: Sizing, spot vs reserved, optimization ROI.

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According to DataEngPrep.tech, this is one of the most frequently asked Spark/Big Data interview questions, reported at 1 company. DataEngPrep.tech maintains a curated database of 1,863+ real data engineering interview questions across 7 categories, verified by industry professionals.

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