Quick Answer
The answer is to query sys.dm_tran_locks and sys.dm_os_waiting_tasks together. This is correct because identifying a blocking chain in Azure SQL Managed Instance requires both lock metadata and wait information: sys.dm_tran_locks shows which resources (such as RID, KEY, PAGE, or OBJECT) are locked and by which session, while sys.dm_os_waiting_tasks reveals which sessions are blocked and the blocking session ID, allowing you to trace the chain from the blocked query back to the root blocker. On the DP-300 exam, this tests your ability to diagnose performance degradation caused by lock contention, a common scenario in managed database environments. A frequent trap is querying only one DMV—sys.dm_tran_locks alone shows locks but not the blocking relationship, and sys.dm_os_waiting_tasks alone shows waits but not the locked resource. For a memory tip, think “locks for the what, waits for the who”—locks identify the resource, waits identify the chain.
This DP-300 practice question tests your understanding of plan and implement data platform resources. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 Managed Instance that is experiencing performance degradation. You suspect a query is causing excessive blocking. You need to identify the blocking chain and the resource holding the lock. Which DMV should you query?
sys.dm_exec_requests
Why wrong: Shows requests but not lock details or waiting tasks.
sys.dm_tran_locks and sys.dm_os_waiting_tasks
These DMVs together provide lock information and waiting tasks to identify blocking.
sys.dm_exec_query_stats
Why wrong: Provides aggregated query performance, not current blocking.
sys.dm_tran_active_snapshot_database_transactions
Why wrong: Used for snapshot isolation transactions, not blocking chains.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
sys.dm_tran_locks and sys.dm_os_waiting_tasks
To identify the blocking chain and the specific resource holding the lock, you need to combine lock metadata with wait information. sys.dm_tran_locks shows current locks and their resource types (e.g., RID, KEY, PAGE, OBJECT), while sys.dm_os_waiting_tasks reveals which sessions are waiting on those locks and the blocking session ID. Together, these DMVs allow you to trace the blocking chain from the blocked session back to the blocker and pinpoint the exact resource causing contention.
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.
sys.dm_exec_requests
Why it's wrong here
Shows requests but not lock details or waiting tasks.
sys.dm_tran_locks and sys.dm_os_waiting_tasks
Why this is correct
These DMVs together provide lock information and waiting tasks to identify blocking.
Related concept
Read the scenario before looking for a memorised answer.
sys.dm_exec_query_stats
Why it's wrong here
Provides aggregated query performance, not current blocking.
sys.dm_tran_active_snapshot_database_transactions
Why it's wrong here
Used for snapshot isolation transactions, not blocking chains.
Common exam traps
The trap here is that candidates often pick sys.dm_exec_requests (Option A) because it shows wait_type and blocking_session_id, but it lacks the granular lock resource information (e.g., RID, KEY) that sys.dm_tran_locks provides, which is essential for identifying the exact resource holding the lock.
Trap categories for this question
Command / output trap
Shows requests but not lock details or waiting tasks.
Detailed technical explanation
Under the hood, sys.dm_tran_locks exposes lock_owner_address and resource_description columns that can be joined with sys.dm_os_waiting_tasks via the wait_resource field to map a waiting session to the exact lock being held. In a real-world scenario, you might join these DMVs with sys.dm_exec_requests and sys.dm_exec_sql_text to get the blocking query text, but the core identification of the blocking chain and lock resource requires the pair in Option B. A subtle behavior: sys.dm_os_waiting_tasks includes a blocking_session_id column, but for parallel queries, a single session can have multiple tasks waiting on different locks, so you must aggregate carefully.
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
Plan and implement data platform resources — This question tests Plan and implement data platform resources — Read the scenario before looking for a memorised answer..
The correct answer is: sys.dm_tran_locks and sys.dm_os_waiting_tasks — To identify the blocking chain and the specific resource holding the lock, you need to combine lock metadata with wait information. sys.dm_tran_locks shows current locks and their resource types (e.g., RID, KEY, PAGE, OBJECT), while sys.dm_os_waiting_tasks reveals which sessions are waiting on those locks and the blocking session ID. Together, these DMVs allow you to trace the blocking chain from the blocked session back to the blocker and pinpoint the exact resource causing contention.
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 24, 2026
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