Question 398 of 919
DP-300 Log write latency Practice Question
Your Azure SQL Managed Instance is experiencing high latency for write transactions. You have identified that log write latency is the bottleneck. The instance uses Premium SSD with 5000 IOPS and 200 MB/s throughput. You observe that the log file is 500 GB and has grown significantly. What is the most likely cause and solution?
⚠ Common exam trap
Many candidates mistakenly believe shrinking a large log file improves write performance, but it actually degrades it due to increased fragmentation.
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
✓
The disk is not fast enough for random writes; switch to Ultra Disk.
For Azure SQL Managed Instance, log write latency is critical for transaction write performance. Premium SSD P30 with 5000 IOPS and 200 MB/s throughput may become a bottleneck under heavy write workloads. Switching to Azure Ultra Disk provides significantly lower latency and higher IOPS/throughput, which can reduce log write latency. Option D is incorrect because shrinking the transaction log does not improve performance and can cause severe fragmentation and performance degradation. Proper log backup scheduling is the correct method to manage log size.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Increase the log file size to allow better write performance.
Why it's wrong here
Increasing the log file size can reduce auto-growth events but does not address the underlying IOPS/throughput limit; it may even increase write latency if the log is already large.
- ✗
The instance has insufficient CPU; scale up the managed instance.
Why it's wrong here
While CPU can affect overall performance, the bottleneck is specifically log write latency, which is storage-related, not CPU-bound.
- ✓
The disk is not fast enough for random writes; switch to Ultra Disk.
Why this is correct
Correct. Ultra Disk provides very low latency and high throughput for sequential writes, directly addressing the log write latency bottleneck.
- ✗
The log file is too large causing fragmentation; shrink it to reduce latency.
Why it's wrong here
Incorrect. Shrinking the transaction log is discouraged because it fragments VLFs and degrades performance; the proper approach is to manage log size through regular log backups and appropriate sizing.
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Last reviewed: Jun 21, 2026
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