Quick Answer
The answer is an I/O subsystem bottleneck. This wait type occurs when a query requests a data page that is not already cached in the buffer pool, forcing a synchronous read from disk; the "SH" suffix specifically indicates a shared latch for reading, and when it dominates wait statistics, it means the storage layer cannot deliver pages fast enough to keep up with demand. On the DP-300 exam, this scenario tests your ability to distinguish between logical (CPU or memory) and physical (I/O) performance issues—a common trap is confusing PAGEIOLATCH_SH with PAGEIOLATCH_EX (which involves writes) or with non-I/O latches like LCK_M_SCH_S. Remember the mnemonic: "I/O Latch = I/O Slow"—if the top wait is PAGEIOLATCH_SH, your first diagnostic step should be checking Azure SQL Database DTU or vCore metrics for high data IO or log IO percentages, not tuning queries or indexes.
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 have an Azure SQL Database with a heavy workload. You notice that the `PAGEIOLATCH_SH` wait is the top wait. Which performance issue does this indicate?
Blocking
Why wrong: Blocking shows `LCK_M_*` waits.
CPU bottleneck
Why wrong: CPU bottlenecks show `SOS_SCHEDULER_YIELD` waits.
I/O subsystem bottleneck
`PAGEIOLATCH_SH` indicates slow I/O for reading pages.
Memory pressure
Why wrong: Memory pressure causes `PAGEIOLATCH` but the primary issue is I/O.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
I/O subsystem bottleneck
The `PAGEIOLATCH_SH` wait type indicates that a query is waiting for a data page to be read from disk into the buffer pool. Since this is the top wait, it points to an I/O subsystem bottleneck where the storage cannot keep up with the demand for reading pages, causing performance degradation.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Blocking
Why it's wrong here
Blocking shows `LCK_M_*` waits.
CPU bottleneck
Why it's wrong here
CPU bottlenecks show `SOS_SCHEDULER_YIELD` waits.
I/O subsystem bottleneck
Why this is correct
`PAGEIOLATCH_SH` indicates slow I/O for reading pages.
Related concept
Read the scenario before looking for a memorised answer.
Memory pressure
Why it's wrong here
Memory pressure causes `PAGEIOLATCH` but the primary issue is I/O.
Common exam traps
The trap here is that candidates confuse `PAGEIOLATCH_SH` with memory pressure or blocking, but the key distinction is that this wait type specifically measures I/O latency for reading pages from disk, not memory availability or lock contention.
Trap categories for this question
Command / output trap
Blocking shows `LCK_M_*` waits.
Detailed technical explanation
`PAGEIOLATCH_SH` is a shared latch wait that occurs when a session needs to read a page from disk into the buffer pool and must wait for the I/O operation to complete. Under the hood, the latch is held only during the physical read; if the buffer pool is large enough, subsequent reads may find the page already cached. In real-world scenarios, this wait often spikes during large index scans or when the database is on slow storage like standard-tier Azure SQL Database or a misconfigured Premium tier with insufficient IOPS.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
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FAQ
Monitor, configure, and optimize database resources — This question tests Monitor, configure, and optimize database resources — Read the scenario before looking for a memorised answer..
The correct answer is: I/O subsystem bottleneck — The `PAGEIOLATCH_SH` wait type indicates that a query is waiting for a data page to be read from disk into the buffer pool. Since this is the top wait, it points to an I/O subsystem bottleneck where the storage cannot keep up with the demand for reading pages, causing performance degradation.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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