DP-300 Practice Question: Monitor, configure, and optimize database resources
You are managing an Azure SQL Database that is experiencing intermittent performance degradation. Query Store shows that a specific query's execution plan changed, causing increased CPU usage. You need to ensure consistent performance without rewriting the application. What should you do?
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
✓
Force the previous query plan using Query Store
Force the previous query plan using Query Store. This approach directly addresses the root cause by locking the query to a known good plan, ensuring consistent performance without application changes. Option A is incorrect because increasing the DTU/service tier may temporarily improve performance but does not fix the plan regression. Option B is incorrect because creating a missing index recommendation may help but does not guarantee the query will use the previous plan. Option C is incorrect because dropping and recreating the index is disruptive and may not force the plan to revert.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Increase the DTU/service tier of the database
Why it's wrong here
Increasing resources addresses symptoms but not the root cause of plan regression.
- ✗
Create a missing index recommendation
Why it's wrong here
A missing index recommendation addresses scan or sort cost, not plan regression; the stem's CPU spike stems from a changed plan for an existing query. Missing indexes suit workloads with genuinely absent supporting indexes. Plan forcing, via Query Store, pins the previously good plan without application changes.
- ✗
Drop and recreate the index used by the query
Why it's wrong here
Dropping and recreating the index rebuilds statistics and may temporarily alter plans, but it does not pin a specific known-good plan and risks recurrence. Rebuilding suits fragmentation or corruption. Query Store plan forcing explicitly binds the query to its previous plan, ensuring consistency.
- ✓
Force the previous query plan using Query Store
Why this is correct
Forcing the previous plan through Query Store pins the known-good execution plan, bypassing the regressed plan chosen by the optimiser. This restores consistent CPU performance without application changes, directly satisfying the requirement to avoid rewriting code. Plan forcing applies immediately to the identified query, resolving the intermittent degradation.
Go deeper
Related to this question
Learn chapter
Monitoring Database Performance with Azure Tools
Key term
Query Store
Query Store is a built-in SQL Server feature that captures and stores a history of query execution plans and performance data for easy monitoring and troubleshooting.
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.
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