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RAN-DBDEA-00135
Ranvier · DBDEA

Exam DBDEA Topics: transformation Difficulty: easy

A junior engineer chains several DataFrame operations in a notebook: two withColumn calls, a filter on status, and a select of five columns. Each cell returns almost instantly, and she is surprised that the source table is only read minutes later, when she finally calls count(). She asks her lead what happened. Which explanation is correct?

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  1. A. Each transformation executed immediately and stored its result; count() only aggregated the precomputed data.
  2. B. Transformations are lazy and only extend the logical plan; count() is an action that triggers execution.
  3. C. Actions are lazy as well; only show() forces Spark to execute the plan and read the source data.
  4. D. The accumulated plan is executed automatically at cluster shutdown, when pending work is flushed to storage.
Reveal answer

Correct answer: Transformations are lazy and only extend the logical plan; count() is an action that triggers execution.

Reference: https://docs.databricks.com/aws/en/pyspark/reference

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Official Answer (B): Transformations are lazy and only extend the logical plan; count() is an action that triggers execution.

⚓ Official Documentation Anchor: https://docs.databricks.com/aws/en/pyspark/reference
Ranvier · DBDEA

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