DP-300 Tip: Master Query Store Before Your Exam (And Your Next DBA Job)

Learn Query Store Beyond Theory

Many DP-300 candidates memorize what Query Store is, but the exam and real-world DBA work expects you to understand when and how to use it.

You should know how to:

Enable Query Store
Identify regressed queries
Compare execution plans
Force a better execution plan
Monitor top resource-consuming queries
Configure Query Store settings

What Query Store does

Query Store automatically captures:

Query text
Execution plans
Runtime statistics
CPU usage
Duration
Logical reads
Plan history

It allows you to compare historical and current performance, making it one of the most valuable troubleshooting tools available in SQL Server and Azure SQL Database.

Example

Enable Query Store

ALTER DATABASE SalesDB
SET QUERY_STORE = ON;

Check Current Status

SELECT
    desired_state_desc,
    actual_state_desc,
    current_storage_size_mb
FROM sys.database_query_store_options;

Why It Matters

Imagine a query that normally runs in 2 seconds suddenly takes 45 seconds after a deployment.

Without Query Store:

You don’t know when performance changed.
The previous execution plan is lost.
Troubleshooting becomes guesswork.

With Query Store:

Compare old and new execution plans.
Identify performance regressions.
Force a previously efficient execution plan if appropriate.
Restore application performance quickly.

This is a common scenario in both the DP-300 exam and production environments.

DP-300 Exam Tip

Know these built-in Query Store reports in SQL Server Management Studio (SSMS):

Top Resource Consuming Queries
Regressed Queries
Overall Resource Consumption
Queries with High Variation
Tracked Queries

Understanding what each report shows is more valuable than simply remembering their names.

Pro Tip

Don’t just read about Query Store. Practice it.

Create a small test database, enable Query Store, execute the same query with different parameters, update statistics or indexes, and observe how execution plans and runtime statistics change over time. Hands-on experience makes the concepts much easier to understand and remember.