DP-300 Practice Question: Monitor, configure, and optimize database resources
You are monitoring an Azure SQL Database using sys.dm_db_wait_stats. You see a high percentage of WRITELOG waits. What is the most likely cause?
⚠ Common exam trap
DP-300 often tests whether candidates can map wait types to root causes — the trap is confusing WRITELOG (log I/O) with PAGELATCH (tempdb allocation) or LCK (blocking).
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 transaction log is on a slow I/O subsystem.
WRITELOG waits occur when a session is waiting for the transaction log to be written to disk, typically at commit time. A high percentage of WRITELOG waits therefore points to slow transaction log I/O — the log disk cannot keep up with the write rate, so commits stall.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Tempdb has allocation contention.
Why it's wrong here
WRITELOG waits indicate transaction log write latency, typically from slow log I/O or frequent commits, not tempdb allocation. Tempdb contention surfaces as PAGELATCH waits on allocation pages, so this misattributes the bottleneck. Tempdb tuning would be correct for PAGELATCH_UP or PAGELATCH_EX waits on tempdb pages under heavy concurrent workload.
- ✓
The transaction log is on a slow I/O subsystem.
Why this is correct
WRITELOG waits occur when sessions wait for transaction log writes to complete. A high proportion indicates the log's I/O subsystem cannot keep pace with commit throughput, making slow log storage the direct cause rather than data file or CPU contention.
- ✗
Queries are blocked by locks.
Why it's wrong here
Blocking shows lock waits, not WRITELOG.
- ✗
CPU is under pressure.
Why it's wrong here
WRITELOG waits measure time spent flushing transaction log records to durable storage, so they point to log I/O latency, not processor contention. It is tempting because CPU pressure produces its own waits (SOS_SCHEDULER_YIELD), but those are distinct wait types and would not dominate WRITELOG.
Go deeper
Related to this question
Learn chapter
Monitoring Database Performance with Azure Tools
Key term
Azure SQL Performance Tuning
Azure SQL Performance Tuning is the process of optimizing the speed and efficiency of queries and database operations in Microsoft Azure SQL Database or SQL Managed Instance to reduce latency and improve throughput.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Microsoft exam blueprint
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