DP-203 Develop data processing Practice Question
You have a dedicated SQL pool in Azure Synapse that stores a fact table with over 100 billion rows. Query performance is degrading over time. You notice that the table is hash-distributed on a column with many duplicate values. What is the most likely impact?
⚠ Common exam trap
A common mix-up: candidates confuse distribution skew with partitioning or statistics issues, but the key clue is the mention of 'many duplicate values' in the hash-distributed column, which directly points to data skew as the root cause.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Data is unevenly distributed across distributions, causing some distributions to be overloaded.
D is correct because a hash-distributed table with a column that has many duplicate values leads to data skew. When the hash function maps many rows to the same distribution, some distributions become overloaded with data while others are underutilized. This imbalance causes query performance to degrade as the overloaded distributions become bottlenecks for processing.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Statistics on the table are outdated.
Why it's wrong here
Outdated statistics can cause poor plans but not directly due to duplicates.
- ✗
The table is not properly partitioned.
Why it's wrong here
Partitioning is separate from distribution.
- ✗
Data compression is not working efficiently.
Why it's wrong here
Compression is independent of distribution column.
- ✓
Data is unevenly distributed across distributions, causing some distributions to be overloaded.
Why this is correct
Duplicate values in hash column cause skew.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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