DP-300 Practice Question: Monitor, configure, and optimize database resources
You are tuning a query in Azure SQL Database that uses a nonclustered columnstore index. The query is supposed to use batch mode execution but shows row mode. What is the most likely 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
✓
The query does not have enough memory grant
Batch mode execution requires a sufficient memory grant. If the query does not get enough memory, it falls back to row mode. Option B is incorrect: while compatibility level 130 or higher is required for batch mode, the question states the index is a nonclustered columnstore index, and the most common cause of row mode despite having such an index is insufficient memory. Option C is incorrect: a filter predicate on a columnstore index does not prevent batch mode. Option D is incorrect: MAXDOP 1 does not disable batch mode; batch mode can work with a single degree of parallelism.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The query does not have enough memory grant
Why this is correct
Insufficient memory grant forces row mode execution.
- ✗
The database compatibility level is below 130
Why it's wrong here
Compatibility level 130+ supports batch mode.
- ✗
The index is defined with a filter predicate
Why it's wrong here
Filtered columnstore indexes still support batch mode.
- ✗
The query hint MAXDOP 1 is used
Why it's wrong here
Batch mode works with single DOP.
Go deeper
Related to this question
Learn chapter
Overview of Azure Data Platform Options
Key term
Azure SQL Performance Tuning
Azure SQL Performance Tuning is the process of optimizing the speed and efficiency of queries and database operations in Microsoft Azure SQL Database or SQL Managed Instance to reduce latency and improve throughput.
Key term
Azure SQL Indexes
Structures in Azure SQL Database that speed up data retrieval by providing quick access paths to rows, similar to a book index.
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