- A
Change the source database to use synchronous replication with DMS
Why wrong: Synchronous replication would slow down the source and is not supported for DMS logical replication.
- B
Reduce the maximum WAL size (max_wal_size) on the source to generate smaller logs
Why wrong: Reducing max_wal_size might cause more frequent WAL switches but does not help DMS keep up; it could even increase overhead.
- C
Increase the wal_keep_segments parameter on the source and enable parallel apply on the destination Cloud SQL instance
Higher wal_keep_segments retains more WAL for DMS to read; parallel apply speeds up replication on the destination.
- D
Increase the maintenance_work_mem parameter on the source database
Why wrong: maintenance_work_mem affects maintenance operations (VACUUM, etc.) and does not impact replication lag.
PCD Practice Question: Manage a Solution that Can Span Multiple Database Systems
This PCD practice question tests your understanding of manage a solution that can span multiple database systems. 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.
A company is migrating an on-premises PostgreSQL database to Cloud SQL for PostgreSQL using Database Migration Service (DMS). During the continuous migration phase, the source database has high write throughput, and the DMS job is falling behind. The replication lag is increasing over time. What should the engineer do to reduce lag?
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
Increase the wal_keep_segments parameter on the source and enable parallel apply on the destination Cloud SQL instance
Option C is correct because increasing wal_keep_segments on the source ensures that more WAL segments are retained, preventing DMS from failing to fetch required logs due to premature cleanup. Enabling parallel apply on the Cloud SQL destination allows multiple transactions to be applied concurrently, reducing the time needed to catch up with the source's high write throughput.
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.
- ✗
Change the source database to use synchronous replication with DMS
Why it's wrong here
Synchronous replication would slow down the source and is not supported for DMS logical replication.
- ✗
Reduce the maximum WAL size (max_wal_size) on the source to generate smaller logs
Why it's wrong here
Reducing max_wal_size might cause more frequent WAL switches but does not help DMS keep up; it could even increase overhead.
- ✓
Increase the wal_keep_segments parameter on the source and enable parallel apply on the destination Cloud SQL instance
Why this is correct
Higher wal_keep_segments retains more WAL for DMS to read; parallel apply speeds up replication on the destination.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Increase the maintenance_work_mem parameter on the source database
Why it's wrong here
maintenance_work_mem affects maintenance operations (VACUUM, etc.) and does not impact replication lag.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse WAL-related parameters (max_wal_size vs. wal_keep_segments) or assume that increasing maintenance memory or changing replication mode can fix replication lag, when the real solution involves retaining more WAL on the source and applying changes faster on the destination.
Detailed technical explanation
How to think about this question
DMS for PostgreSQL uses logical replication slots to stream changes; wal_keep_segments (or wal_keep_size in newer versions) prevents the source from recycling WAL segments that the replication slot still needs. Parallel apply leverages multiple worker processes on the destination to apply transactions in parallel, which is critical when the source has high write concurrency, as single-threaded apply can become a bottleneck.
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 PCD question test?
Manage a Solution that Can Span Multiple Database Systems — This question tests Manage a Solution that Can Span Multiple Database Systems — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Increase the wal_keep_segments parameter on the source and enable parallel apply on the destination Cloud SQL instance — Option C is correct because increasing wal_keep_segments on the source ensures that more WAL segments are retained, preventing DMS from failing to fetch required logs due to premature cleanup. Enabling parallel apply on the Cloud SQL destination allows multiple transactions to be applied concurrently, reducing the time needed to catch up with the source's high write throughput.
What should I do if I get this PCD question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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Last reviewed: Jul 4, 2026
This PCD 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 PCD exam.
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