The answer is to define the column with the `allow_commit_timestamp` option and set it to 'true'. This approach is correct because Cloud Spanner’s commit timestamp feature automatically records the exact commit time of the last mutation on each row, eliminating the need for a separate read operation to retrieve that timestamp. By designing a commit timestamp column in this way, you directly reduce read latency for queries like “orders placed in the last hour,” since Spanner can efficiently filter rows based on the stored commit time without additional joins or index lookups. On the Google Professional Cloud Database Engineer exam, this question tests your understanding of Spanner’s schema design for optimizing read-heavy workloads; a common trap is confusing commit timestamps with generated columns or secondary indexes, which add write overhead or cannot auto-populate. Remember the mnemonic “ACT” — Allow_commit_timestamp, Commit time auto-stored, reduces Read latency.
PCDE Design and implement database schemas Practice Question
This PCDE practice question tests your understanding of design and implement database schemas. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
In Cloud Spanner, a table 'Orders' has a primary key (OrderId INT64) and is frequently updated. The application often queries for orders placed in the last hour. To reduce read latency, you decide to add a column to store the commit timestamp. Which approach should you use?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Define the column with the `allow_commit_timestamp` option and set it to 'true'
Option D is correct: Spanner allows defining a column with commit timestamp option, which automatically records the commit time of the last mutation. This eliminates the need to read the column separately. Option A (interleaved tables) does not provide the timestamp. Option B (secondary index) adds write overhead. Option C (generated column) cannot be automatically populated with commit time.
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.
✓
Define the column with the `allow_commit_timestamp` option and set it to 'true'
Why this is correct
Spanner automatically assigns the commit timestamp to such columns, enabling efficient time-based queries.
Clue confirmation
The clue word "primary" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
Create an interleaved table with the timestamp
Why it's wrong here
Interleaving does not automatically store commit timestamps.
✗
Use a generated column with expression to get current_timestamp
Why it's wrong here
Generated columns are computed at read time, not at write time.
✗
Add a secondary index on a user-managed timestamp column
Why it's wrong here
Secondary indexes add write latency and do not guarantee the latest timestamp.
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.
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: Define the column with the `allow_commit_timestamp` option and set it to 'true' — Option D is correct: Spanner allows defining a column with commit timestamp option, which automatically records the commit time of the last mutation. This eliminates the need to read the column separately. Option A (interleaved tables) does not provide the timestamp. Option B (secondary index) adds write overhead. Option C (generated column) cannot be automatically populated with commit time.
What should I do if I get this PCDE question wrong?
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.
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?
Static NAT maps one inside address to one outside address.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This PCDE practice question is part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCDE exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.