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Question 132 of 1,000

Design and implement database schemas →hardMultiple ChoiceObjective-mapped

PCDE Design and implement database schemas Practice Question

This PCDE practice question tests your understanding of design and implement database schemas. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.

Your company runs an e-commerce platform on Google Cloud. The platform uses Cloud SQL for MySQL to store product inventory. The inventory table has the following schema: CREATE TABLE inventory (product_id INT PRIMARY KEY, quantity INT, last_updated TIMESTAMP) ENGINE=InnoDB. The application performs frequent updates on quantity for a subset of popular products. Recently, you have noticed increased deadlock errors during peak hours. The application uses REPEATABLE READ isolation level. You suspect that the schema design is contributing to locking contention. After analyzing the workload, you find that the updates often involve incrementing or decrementing quantity by small amounts and are mostly on the same set of popular products. What would be the best course of action to reduce deadlocks without compromising data integrity?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.

A
Rewrite the update query to use atomic operations (e.g., UPDATE inventory SET quantity = quantity - ? WHERE product_id = ?) without pre-fetching the current value.
Atomic updates avoid the need for SELECT ... FOR UPDATE and significantly reduce locking and deadlock chances.
B
Change the engine to MyISAM to avoid row-level locking.
Why wrong: MyISAM uses table-level locking which would cause even more contention, and is not supported on Cloud SQL for MySQL.
C
Partition the inventory table by product_id range to spread the load.
Why wrong: Partitioning might help with distribution but does not directly address the deadlock pattern caused by read-before-write on the same rows.
D
Reduce the isolation level to READ COMMITTED to reduce locking.
Why wrong: While this may reduce locking, it can lead to non-repeatable reads and is not the most effective solution for deadlocks caused by specific query pattern.

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

✓

Rewrite the update query to use atomic operations (e.g., UPDATE inventory SET quantity = quantity - ? WHERE product_id = ?) without pre-fetching the current value.

Option A is correct because the application's pattern of reading the current quantity before updating (e.g., SELECT quantity FROM inventory WHERE product_id = ?, then UPDATE inventory SET quantity = ? WHERE product_id = ?) causes gap locks and deadlocks under REPEATABLE READ. By using an atomic UPDATE (UPDATE inventory SET quantity = quantity - ? WHERE product_id = ?), the database performs the update without a prior read, reducing lock contention. This maintains data integrity because the subtraction is atomic and accurate. Option B is wrong because MyISAM does not support transactions or row-level locking, which compromises data integrity. Option C is wrong because partitioning does not reduce locking contention on the same rows; it only improves data management. Option D is wrong because reducing isolation to READ COMMITTED may reduce some locking but introduces non-repeatable reads and does not address the fundamental read-before-write pattern that causes deadlocks.

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.

✓
Rewrite the update query to use atomic operations (e.g., UPDATE inventory SET quantity = quantity - ? WHERE product_id = ?) without pre-fetching the current value.
Why this is correct
Atomic updates avoid the need for SELECT ... FOR UPDATE and significantly reduce locking and deadlock chances.
Clue confirmation
The clue word "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Change the engine to MyISAM to avoid row-level locking.
Why it's wrong here
MyISAM uses table-level locking which would cause even more contention, and is not supported on Cloud SQL for MySQL.
✗
Partition the inventory table by product_id range to spread the load.
Why it's wrong here
Partitioning might help with distribution but does not directly address the deadlock pattern caused by read-before-write on the same rows.
✗
Reduce the isolation level to READ COMMITTED to reduce locking.
Why it's wrong here
While this may reduce locking, it can lead to non-repeatable reads and is not the most effective solution for deadlocks caused by specific query pattern.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.

Detailed technical explanation

How to think about this question

This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.

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.
Use explanations to understand the rule behind the answer.

TExam Day Tips

Underline the problem statement mentally.
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 PCDE exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.

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FAQ

Questions learners often ask

What does this PCDE question test?

Design and implement database schemas — This question tests Design and implement database schemas — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: Rewrite the update query to use atomic operations (e.g., UPDATE inventory SET quantity = quantity - ? WHERE product_id = ?) without pre-fetching the current value. — Option A is correct because the application's pattern of reading the current quantity before updating (e.g., SELECT quantity FROM inventory WHERE product_id = ?, then UPDATE inventory SET quantity = ? WHERE product_id = ?) causes gap locks and deadlocks under REPEATABLE READ. By using an atomic UPDATE (UPDATE inventory SET quantity = quantity - ? WHERE product_id = ?), the database performs the update without a prior read, reducing lock contention. This maintains data integrity because the subtraction is atomic and accurate. Option B is wrong because MyISAM does not support transactions or row-level locking, which compromises data integrity. Option C is wrong because partitioning does not reduce locking contention on the same rows; it only improves data management. Option D is wrong because reducing isolation to READ COMMITTED may reduce some locking but introduces non-repeatable reads and does not address the fundamental read-before-write pattern that causes deadlocks.

What should I do if I get this PCDE question wrong?

Are there clue words in this question I should notice?

Yes — watch for: "primary". Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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