- A
Define the column with the `allow_commit_timestamp` option and set it to 'true'
Spanner automatically assigns the commit timestamp to such columns, enabling efficient time-based queries.
- B
Create an interleaved table with the timestamp
Why wrong: Interleaving does not automatically store commit timestamps.
- C
Use a generated column with expression to get current_timestamp
Why wrong: Generated columns are computed at read time, not at write time.
- D
Add a secondary index on a user-managed timestamp column
Why wrong: Secondary indexes add write latency and do not guarantee the latest timestamp.
Question 925 of 1,000
Cloud Spanner Commit Timestamp Column — Reduce Read Latency
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.
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.
Quick Answer
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.
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
✓
Define the column with the `allow_commit_timestamp` option and set it to 'true'
Option A is correct because Cloud Spanner's `allow_commit_timestamp` option, when set to 'true' on a column of type `TIMESTAMP`, automatically populates that column with the exact commit timestamp of the transaction. This enables efficient time-based queries (e.g., orders placed in the last hour) without requiring application-managed timestamps or additional writes, reducing read latency by leveraging Spanner's built-in commit-time visibility.
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.
- ✓
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
Read the scenario before looking for a memorised answer.
- ✗
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: answer the scenario, not the keyword
This question tests the misconception that generated columns or secondary indexes can substitute for Spanner's native commit timestamp feature, but only `allow_commit_timestamp` guarantees the exact commit time without application overhead.
Detailed technical explanation
How to think about this question
Under the hood, the `allow_commit_timestamp` column uses Spanner's TrueTime API to assign a globally consistent timestamp at commit time, ensuring linearizability. This is particularly valuable in multi-region deployments where clock skew could otherwise cause inaccuracies in user-managed timestamps. A real-world scenario is auditing or time-windowed analytics, where relying on application-set timestamps could miss or duplicate records due to retries or partial failures.
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.
- →
Design and implement database schemas — study guide chapter
Learn the concepts, then practise the questions
- →
Design and implement database schemas practice questions
Targeted practice on this topic area only
- →
All PCDE questions
1,000 questions across all exam domains
- →
Google Professional Cloud Database Engineer study guide
Full concept coverage aligned to exam objectives
- →
PCDE practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related PCDE practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Building and Implementing CI/CD Pipelines for a Service practice questions
Practise PCDE questions linked to Building and Implementing CI/CD Pipelines for a Service.
Bootstrapping a Google Cloud Organisation for DevOps practice questions
Practise PCDE questions linked to Bootstrapping a Google Cloud Organisation for DevOps.
Applying Site Reliability Engineering Practices to a Service practice questions
Practise PCDE questions linked to Applying Site Reliability Engineering Practices to a Service.
Implementing Service Monitoring Strategies practice questions
Practise PCDE questions linked to Implementing Service Monitoring Strategies.
Optimising Service Performance practice questions
Practise PCDE questions linked to Optimising Service Performance.
Plan and manage database infrastructure practice questions
Practise PCDE questions linked to Plan and manage database infrastructure.
Define data structures and implement SQL for Business Intelligence practice questions
Practise PCDE questions linked to Define data structures and implement SQL for Business Intelligence.
Design and implement database schemas practice questions
Practise PCDE questions linked to Design and implement database schemas.
Monitor and optimize database performance practice questions
Practise PCDE questions linked to Monitor and optimize database performance.
PCDE fundamentals practice questions
Practise PCDE questions linked to PCDE fundamentals.
PCDE scenario practice questions
Practise PCDE questions linked to PCDE scenario.
PCDE troubleshooting practice questions
Practise PCDE questions linked to PCDE troubleshooting.
Practice this exam
Start a free PCDE practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
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: Define the column with the `allow_commit_timestamp` option and set it to 'true' — Option A is correct because Cloud Spanner's `allow_commit_timestamp` option, when set to 'true' on a column of type `TIMESTAMP`, automatically populates that column with the exact commit timestamp of the transaction. This enables efficient time-based queries (e.g., orders placed in the last hour) without requiring application-managed timestamps or additional writes, reducing read latency by leveraging Spanner's built-in commit-time visibility.
What should I do if I get this PCDE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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.
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 →
Keep practising
More PCDE practice questions
- A company stores sensor data in BigQuery. They have a table 'sensor_readings' with columns: sensor_id, reading_time, val…
- Which THREE are valid considerations when designing BigQuery tables for BI reporting?
- A company uses Cloud Build to build Docker images. They want to cache intermediate layers to speed up subsequent builds.…
- A company is adopting GitOps for their GKE clusters using Config Sync. They need to meet the following requirements: (1)…
- A team is migrating an on-premises PostgreSQL database to Cloud SQL for PostgreSQL. The existing schema uses a large num…
- A DevOps engineer is setting up Docker credential helper for Artifact Registry on a Cloud Build worker. They want the bu…
Last reviewed: Jul 4, 2026
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.