- A
Schedule the schema change during a period of low traffic.
Even though Spanner DDL is online, performing it during low traffic minimizes any potential performance impact.
- B
Disable the table, add the column, then re-enable.
Why wrong: Disabling the table causes downtime; Spanner can add columns without disabling.
- C
Add the column with a NULL default value to avoid backfilling existing rows.
Adding a NULL column is instantaneous in Spanner as it only updates metadata.
- D
Use ALTER TABLE ADD COLUMN with IF NOT EXISTS to avoid errors if the column already exists.
Spanner supports online DDL; IF NOT EXISTS prevents failures without downtime.
- E
Create a new table with the column, then copy data in batches.
Why wrong: This approach requires data migration and likely downtime, and it's not recommended for simple schema changes.
Quick Answer
The answer is to schedule the schema change during low traffic periods, use ALTER TABLE ADD COLUMN with IF NOT EXISTS, and rely on Cloud Spanner’s online schema change capability. This is correct because Cloud Spanner applies schema changes online without locking the entire table, but heavy write traffic during the operation can still cause transaction conflicts or increased latency; performing the change during a quiet period minimizes these risks, while the IF NOT EXISTS clause prevents errors if the column already exists, avoiding unnecessary rollbacks. On the Google Professional Cloud Database Engineer exam, this scenario tests your understanding of how to minimize downtime with Cloud Spanner online schema changes, often appearing as a multi-select question where a common trap is assuming schema changes require table locks or downtime. A useful memory tip is “Quiet, Check, Online”—schedule during quiet hours, check for existence with IF NOT EXISTS, and trust Spanner’s online processing.
PCDE Plan and manage database infrastructure Practice Question
This PCDE practice question tests your understanding of plan and manage database infrastructure. 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.
A global retail company uses Cloud Spanner to manage product inventory. They need to apply a schema change to add a new column to a table that has 10 billion rows. Which THREE strategies should they consider to minimize downtime?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"minimum / minimize"Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
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
Schedule the schema change during a period of low traffic.
Option A is correct because scheduling schema changes during low traffic reduces the risk of contention and performance impact on the live database. Cloud Spanner applies schema changes online without locking the entire table, but heavy write traffic can still cause transaction conflicts or increased latency; performing the change during a quiet period minimizes these risks.
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.
- ✓
Schedule the schema change during a period of low traffic.
Why this is correct
Even though Spanner DDL is online, performing it during low traffic minimizes any potential performance impact.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Disable the table, add the column, then re-enable.
Why it's wrong here
Disabling the table causes downtime; Spanner can add columns without disabling.
- ✓
Add the column with a NULL default value to avoid backfilling existing rows.
Why this is correct
Adding a NULL column is instantaneous in Spanner as it only updates metadata.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
Use ALTER TABLE ADD COLUMN with IF NOT EXISTS to avoid errors if the column already exists.
Why this is correct
Spanner supports online DDL; IF NOT EXISTS prevents failures without downtime.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Create a new table with the column, then copy data in batches.
Why it's wrong here
This approach requires data migration and likely downtime, and it's not recommended for simple schema changes.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that large tables require data migration or table recreation for schema changes, but Cloud Spanner's online DDL handles column additions without backfilling, making options like B and E unnecessary and counterproductive.
Detailed technical explanation
How to think about this question
Cloud Spanner uses a distributed, synchronous replication architecture where schema changes are applied as a multi-phase operation: first, the schema change is committed to the metadata, then the new column is added to the schema version, and existing rows are not backfilled (the column appears as NULL for existing rows). This allows the ALTER TABLE ADD COLUMN to complete in milliseconds regardless of table size, because no data movement occurs. The IF NOT EXISTS clause (Option D) is a best practice to make the operation idempotent, preventing errors in automated scripts.
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 PCDE question test?
Plan and manage database infrastructure — This question tests Plan and manage database infrastructure — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Schedule the schema change during a period of low traffic. — Option A is correct because scheduling schema changes during low traffic reduces the risk of contention and performance impact on the live database. Cloud Spanner applies schema changes online without locking the entire table, but heavy write traffic can still cause transaction conflicts or increased latency; performing the change during a quiet period minimizes these risks.
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: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Same concept, more angles
1 more ways this is tested on PCDE
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A financial services company uses Cloud Spanner for transaction processing. They need to ensure zero downtime during a schema change that adds a new column with a default value to a large table. Which approach should the Database Engineer take?
hard- A.Create a new table with the new column, then use a fan-out pattern to write to both tables until the old table is deprecated.
- B.Use an ALTER TABLE statement during a maintenance window.
- C.Drop the table and recreate it with the new schema.
- ✓ D.Use ALTER TABLE to add the column; Spanner handles schema changes online.
Why D: Option D is correct because Cloud Spanner supports online schema changes, including adding columns with default values, without requiring a maintenance window or causing downtime. Spanner applies schema updates asynchronously across all nodes while the database remains fully available for reads and writes, making it the ideal approach for zero-downtime requirements.
Last reviewed: Jun 30, 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.
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