The answer is that the parameter group uses an invalid value for 'shared_buffers' because it must be an integer, not a percentage. In Amazon RDS for PostgreSQL, the shared_buffers parameter is a static, integer-based setting that specifies the amount of memory allocated in 8 KB blocks, not a percentage of instance memory. When you attempt to set it to a percentage like 25% in a CloudFormation template, RDS rejects the value as invalid, causing the DBParameterGroup association to fail. This question tests your understanding of RDS parameter group constraints on the AWS Certified Database Specialty DBS-C01 exam, where a common trap is confusing PostgreSQL’s native percentage syntax with RDS’s requirement for explicit integer values. The exam often pairs this with max_connections to see if you know which parameters are modifiable and which require specific formats. Memory tip: think "shared_buffers = blocks, not percentages" — RDS PostgreSQL wants a raw number, so always convert your percentage to an integer by calculating the actual buffer count.
DBS-C01 Deployment and Migration Practice Question
This DBS-C01 practice question tests your understanding of deployment and migration. 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 deploying a new application on Amazon RDS for PostgreSQL. The application requires a database with a specific parameter group that sets 'max_connections' to 500 and 'shared_buffers' to 25% of the instance memory. The company uses CloudFormation to deploy the RDS instance. The CloudFormation template creates a DBInstance with a DBParameterGroup. The deployment fails because the parameter group cannot be associated with the DB instance. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The parameter group uses an invalid value for 'shared_buffers' because it must be an integer, not a percentage.
Option D is correct because RDS does not allow setting 'shared_buffers' as a percentage; it must be an integer value. Option A is wrong because parameter groups can be created in CloudFormation. Option B is wrong because 'max_connections' can be modified. Option C is wrong because the parameter group family must match the engine version.
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.
✓
The parameter group uses an invalid value for 'shared_buffers' because it must be an integer, not a percentage.
Why this is correct
RDS requires absolute values for 'shared_buffers', not percentages.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The 'max_connections' value of 500 exceeds the allowed maximum for the instance class.
Why it's wrong here
Max_connections can be set to 500; it depends on instance memory.
✗
The CloudFormation template does not include a DependsOn clause linking the DBParameterGroup to the DBInstance.
Why it's wrong here
CloudFormation automatically handles dependencies when resources reference each other.
✗
The DBParameterGroup is not in the same region as the DBInstance.
Why it's wrong here
CloudFormation deploys resources in the same region by default.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Identify which DBS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Deployment and Migration — This question tests Deployment and Migration — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The parameter group uses an invalid value for 'shared_buffers' because it must be an integer, not a percentage. — Option D is correct because RDS does not allow setting 'shared_buffers' as a percentage; it must be an integer value. Option A is wrong because parameter groups can be created in CloudFormation. Option B is wrong because 'max_connections' can be modified. Option C is wrong because the parameter group family must match the engine version.
What should I do if I get this DBS-C01 question wrong?
Identify which DBS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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