DP-300 Practice Question: Monitor, configure, and optimize database resources
Exhibit
Refer to the exhibit. SELECT plan_handle, execution_count, total_worker_time, total_logical_reads, total_elapsed_time FROM sys.dm_exec_query_stats ORDER BY total_logical_reads DESC;
You are analyzing query performance in an Azure SQL Database. The query in the exhibit returns a list of queries ordered by total_logical_reads. What does high total_logical_reads typically indicate?
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 query is reading many pages from the buffer pool, possibly due to missing indexes
High total_logical_reads typically indicates that the query is reading many pages from the buffer pool, which often points to missing or inefficient indexes. Option D is correct. Option A is incorrect because high logical reads relate to buffer pool access, not necessarily I/O latency (which is indicated by high physical reads). Option B is incorrect because CPU time is measured by worker_time, not logical reads. Option C is incorrect because while logical reads can increase memory usage, the primary indicator of memory usage is the memory grant, not logical reads.
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 query is experiencing I/O latency
Why it's wrong here
Logical reads count pages read from the buffer pool, so they indicate memory-resident page access volume, not physical I/O latency. I/O latency is tempting because heavy reading sounds I/O-bound, and it would be correct if the metric were physical reads or PAGEIOLATCH waits rather than total_logical_reads.
- ✗
The query is using a lot of CPU time
Why it's wrong here
Logical reads measure buffer pool page accesses, not processor cycles; a query can perform many logical reads with minimal CPU. CPU is tempting because expensive queries often consume both, and it would be correct if the metric were total_worker_time or CPU time rather than total_logical_reads.
- ✗
The query is using a lot of memory
Why it's wrong here
High logical reads reflect pages touched, not memory consumption; a query can read millions of buffer pages while using little workspace memory. Memory is tempting because logical reads occur in the buffer pool, and it would be correct if the metric were granted workspace memory or a memory grant wait.
- ✓
The query is reading many pages from the buffer pool, possibly due to missing indexes
Why this is correct
High total_logical_reads means the query is pulling many 8 KB pages from the buffer pool, indicating it scans more data than necessary. This points to missing or ineffective indexes forcing large scans, satisfying the stem's constraint of diagnosing poor query performance.
Go deeper
Related to this question
Learn chapter
Implementing High Availability for Azure SQL Databases
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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