The answer is that the secondary replica’s log apply rate is slower than the log generation rate on the primary. This is the most likely cause of a high log send queue in an Azure SQL Managed Instance availability group because the queue represents log records that have been sent from the primary but not yet hardened on the secondary. Even with ample primary resources and low network latency, if the secondary replica lacks sufficient CPU, I/O, or memory to apply transactions quickly enough, the backlog grows. On the DP-300 exam, this scenario tests your understanding of the availability group data synchronization flow—specifically that the log send queue is a symptom of a slow secondary, not a primary or network issue. A common trap is to blame network latency or primary resource constraints, but the question explicitly rules those out. Memory tip: think of the log send queue as a “secondary bottleneck” indicator—if the secondary can’t keep up, the queue rises regardless of how fast the primary generates logs.
DP-300 Practice Question: Monitor, configure, and optimize database resources
This DP-300 practice question tests your understanding of monitor, configure, and optimize database resources. 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.
You manage an Azure SQL Database that is part of an Always On availability group in Azure SQL Managed Instance. You notice that the secondary replica is experiencing high log send queue size. The primary replica has ample CPU and I/O resources. The network latency between replicas is low. What is the most likely cause of the high log send queue?
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.
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.
Clue: "always"
Why it matters: Absolute qualifier. An answer using 'always' is only correct if there are genuinely no exceptions — absolute statements are often wrong in networking.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The secondary replica's log apply rate is slower than the log generation rate on the primary.
Option A is correct because if the secondary replica is not able to apply log records quickly enough, the log send queue grows. This can happen if the secondary has insufficient resources or is under load. Option B is wrong because direct network latency is low. Option C is wrong because the primary has ample resources. Option D is wrong because log flush on the primary is not the issue.
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 secondary replica is configured with asynchronous commit.
Why it's wrong here
Asynchronous commit would not cause log send queue; it would cause data loss risk.
✗
The primary replica is experiencing log flush delays.
Why it's wrong here
If primary were slow, log generation would be slow, not queue buildup.
✓
The secondary replica's log apply rate is slower than the log generation rate on the primary.
Why this is correct
A slow secondary can cause backlog, even with fast network.
Clue confirmation
The clue words "most likely", "primary", "always" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The network bandwidth between replicas is insufficient.
Why it's wrong here
Network latency is low, and bandwidth is not specified but unlikely if latency is low.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this DP-300 question in full detail.
Identify which DP-300 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.
Monitor, configure, and optimize database resources — This question tests Monitor, configure, and optimize database resources — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The secondary replica's log apply rate is slower than the log generation rate on the primary. — Option A is correct because if the secondary replica is not able to apply log records quickly enough, the log send queue grows. This can happen if the secondary has insufficient resources or is under load. Option B is wrong because direct network latency is low. Option C is wrong because the primary has ample resources. Option D is wrong because log flush on the primary is not the issue.
What should I do if I get this DP-300 question wrong?
Identify which DP-300 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", "primary", "always". 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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