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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: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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.

Question 1hardmultiple choice

Full question →

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 C is correct because using UPDATE with a WHERE clause that includes the current quantity can cause gap locks and phantom reads; switching to a single atomic UPDATE without checking the current value, and optionally using optimistic locking, reduces locking. Option A is wrong because row-level locking is already used; disabling it is not possible. Option B is wrong because reducing isolation to READ COMMITTED may reduce locking but could cause non-repeatable reads; however, it is a viable option but not the best. Option D is wrong because changing to MyISAM is not supported and also loses transactional integrity. The best solution is to adjust the SQL statement to avoid the read-before-write pattern and rely on atomic operations.

Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.

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 words "best", "primary" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
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: NAT rules depend on direction and matching traffic

NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.

Detailed technical explanation

How to think about this question

NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.

KKey Concepts to Remember

Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.

TExam Day Tips

Identify inside and outside interfaces first.
Check whether the scenario needs static NAT, dynamic NAT or PAT.
Do not confuse NAT matching ACLs with normal packet-filtering intent.

Key takeaway

NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.

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. NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated. 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.

Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PCDE NAT questions on configuration and troubleshooting.

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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 — Static NAT maps one inside address to one outside address..

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 C is correct because using UPDATE with a WHERE clause that includes the current quantity can cause gap locks and phantom reads; switching to a single atomic UPDATE without checking the current value, and optionally using optimistic locking, reduces locking. Option A is wrong because row-level locking is already used; disabling it is not possible. Option B is wrong because reducing isolation to READ COMMITTED may reduce locking but could cause non-repeatable reads; however, it is a viable option but not the best. Option D is wrong because changing to MyISAM is not supported and also loses transactional integrity. The best solution is to adjust the SQL statement to avoid the read-before-write pattern and rely on atomic operations.

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

Are there clue words in this question I should notice?

Yes — watch for: "best", "primary". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.

What is the key concept behind this question?

Static NAT maps one inside address to one outside address.

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