# Certified-Data-Engineer-Professional — Question 427

**Type:** multiple_choice
**Topics:** topic_1

## Question

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.

## Correct Answer

_See scenario._

## Explanation

Selected Answer: C
C. Size on Disk is > 0

When using Spark's MEMORY_ONLY storage level, the ideal scenario is that the data is fully cached in memory, and the Size on Disk should be 0 (indicating that the data is not spilled to disk). If the Size on Disk is greater than 0, it suggests that some data has been spilled to disk, which can lead to degraded performance as reading from disk is slower than reading from memory.

**Reference:** examtopics_top_comment

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Source: https://hiexam.net/q/databricks/Certified-Data-Engineer-Professional/427  
Practice (tracked): https://hiexam.net/study/Certified-Data-Engineer-Professional/practice