Databricks Certified Data Engineer Professional — Question 99

Which indicators would you look for in the Spark UI’s Storage tab to signal that a cached table is not performing optimally? Assume you are using Spark’s MEMORY_ONLY storage level.

Answer options

• A. Size on Disk is < Size in Memory
• B. The RDD Block Name includes the “*” annotation signaling a failure to cache
• C. Size on Disk is > 0
• D. The number of Cached Partitions > the number of Spark Partitions
• E. On Heap Memory Usage is within 75% of Off Heap Memory Usage

Correct answer: C

Explanation

The correct answer is C, as a Size on Disk greater than zero indicates that the data is being cached but may not be fitting optimally in memory. Option A is incorrect because ideally, Size on Disk should not be less than Size in Memory for optimal performance. Options B, D, and E highlight other issues but do not directly indicate suboptimal performance related to caching in MEMORY_ONLY mode.