Databricks Databricks-Certified-Data-Engineer-Associate Exam With Confidence Using Practice Dumps

The OPTIMIZE command in Delta Lake is designed to compact small files into larger files to improve query performance and reduce file system overhead. Importantly, OPTIMIZE is considered an idempotent operation when run on unchanged data. This means that once files have been compacted optimally, running OPTIMIZE again does not produce additional changes unless new small files have been added to the table. Databricks ensures that file compaction is efficient and avoids unnecessary rewrites, which helps control compute costs and maintain stable performance. While features like ZORDER can be applied during OPTIMIZE to improve data skipping, re-running the same command without new data will not further reorganize files. Options A, B, and C incorrectly imply additional restructuring or changes on repeated execution. According to Delta Lake best practices, OPTIMIZE should be run periodically after data ingestion events rather than repeatedly on unchanged datasets. This behavior reinforces predictable performance and efficient resource utilization in Databricks environments.

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The small country lookup DataFrame should be broadcast to the executors. A broadcast join copies the small side of the join to each worker, allowing every executor to join its partition of the billion-row events DataFrame locally. This avoids shuffling the very large DataFrame across the network and is effective when one relation is small enough to fit comfortably in executor memory. Broadcasting events_df would be impractical because it contains billions of rows. Caching or persisting both DataFrames can help when data is reused, but neither action by itself changes the join strategy or removes the expensive shuffle. Databricks exposes the PySpark broadcast function specifically to mark a DataFrame as suitable for a broadcast join. Therefore, option D is the correct optimization.

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