Question 144 of 953

Monitor, configure, and optimize database resources →hardMultiple SelectObjective-mapped

Quick Answer

The correct answers are to update statistics on all tables involved in the query and to create appropriate indexes on the columns used in joins and filters. An Index Spool (Lazy Spool) operator appears when the query engine must build a temporary index on the fly, which is a clear signal that permanent indexing is missing or that the optimizer lacks accurate data distribution information. By creating proper indexes, you eliminate the need for the spool entirely, while updating statistics ensures the optimizer can choose efficient join strategies without resorting to spool operations. On the Microsoft Azure Database Administrator Associate DP-300 exam, this scenario tests your ability to read execution plans and diagnose performance bottlenecks—a common trap is to focus only on indexing while forgetting that stale statistics can also trigger spools. Remember the mnemonic: “Spool means missing tool—index or stats are the rule.”

DP-300 Practice Question: Monitor, configure, and optimize database resources

This DP-300 practice question tests your understanding of monitor, configure, and optimize database resources. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

You are responsible for performance tuning of an Azure SQL Database that hosts a customer relationship management (CRM) application. The database has several tables with millions of rows. Users report that a report query that joins four tables is slow. You examine the query execution plan and notice that the database engine is using an Index Spool (Lazy Spool) operator. Which TWO actions should you take to improve query performance? (Choose two.)

Question 1hardmulti select

Full question →

A
Disable parallelism for the query using the MAXDOP 1 hint.
Why wrong: Disabling parallelism might reduce the spool's cost but does not eliminate it and could slow down other operations.
B
Increase the DTU or vCore count of the database.
Why wrong: Adding resources may reduce the impact but does not address the root cause of the spool.
C
Create appropriate indexes on the columns used in joins and filters.
Proper indexing can allow the optimizer to use index seeks instead of scanning and spooling.
D
Rewrite the query using table hints to force a specific join order.
Why wrong: Forcing a join order may not eliminate the spool and could cause other performance issues.
E
Update statistics on all tables involved in the query.
Updated statistics improve cardinality estimates, helping the optimizer choose a better plan without spools.

Full breakdown with real-world context →

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

✓

Create appropriate indexes on the columns used in joins and filters.

An Index Spool (Lazy Spool) operator in an execution plan indicates that the query engine is creating a temporary index on the fly to support join or filter operations, which is a sign of missing or inadequate permanent indexes. Creating appropriate indexes on the columns used in joins and filters (Option C) eliminates the need for the spool, reducing I/O and improving performance. Updating statistics (Option E) ensures the query optimizer has accurate distribution information to generate efficient plans, which can also help avoid spool operations.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
Disable parallelism for the query using the MAXDOP 1 hint.
Why it's wrong here
Disabling parallelism might reduce the spool's cost but does not eliminate it and could slow down other operations.
✗
Increase the DTU or vCore count of the database.
Why it's wrong here
Adding resources may reduce the impact but does not address the root cause of the spool.
✓
Create appropriate indexes on the columns used in joins and filters.
Why this is correct
Proper indexing can allow the optimizer to use index seeks instead of scanning and spooling.
Related concept
Read the scenario before looking for a memorised answer.
✗
Rewrite the query using table hints to force a specific join order.
Why it's wrong here
Forcing a join order may not eliminate the spool and could cause other performance issues.
✓
Update statistics on all tables involved in the query.
Why this is correct
Updated statistics improve cardinality estimates, helping the optimizer choose a better plan without spools.
Related concept
Read the scenario before looking for a memorised answer.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often assume an Index Spool is always a performance booster (like a regular index seek) or that increasing hardware resources (Option B) is the quick fix, when in fact the spool is a costly workaround for missing permanent indexes and stale statistics.

Detailed technical explanation

How to think about this question

An Index Spool (Lazy Spool) operator works by reading rows from a child operator, building a temporary index in the tempdb database, and then using that index for subsequent operations like joins or aggregations. This is resource-intensive because it involves writing to tempdb and can cause blocking under concurrency. In a real-world CRM with millions of rows, missing indexes on foreign key columns or filter predicates are common culprits, and updating statistics with FULLSCAN can reveal skewed data distributions that the optimizer needs to avoid spools.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.

TExam Day Tips

Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this DP-300 question test?

Monitor, configure, and optimize database resources — This question tests Monitor, configure, and optimize database resources — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: Create appropriate indexes on the columns used in joins and filters. — An Index Spool (Lazy Spool) operator in an execution plan indicates that the query engine is creating a temporary index on the fly to support join or filter operations, which is a sign of missing or inadequate permanent indexes. Creating appropriate indexes on the columns used in joins and filters (Option C) eliminates the need for the spool, reducing I/O and improving performance. Updating statistics (Option E) ensures the query optimizer has accurate distribution information to generate efficient plans, which can also help avoid spool operations.

What should I do if I get this DP-300 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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