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When working with Microsoft Azure SQL Solutions, it is important to monitor and manage sessions effectively. Blocking occurs when one session holds a lock on a resource that another session needs, causing it to wait. This article will guide you through the process of identifying sessions that cause blocking in Azure SQL solutions. You will learn about various methods and techniques to detect and resolve blocking.
To identify blocking sessions, you need to actively monitor your Azure SQL solution. Follow these steps:
Use the sys.dm_exec_requests
view to identify sessions that are currently blocked. Execute the following query:
SELECT *
FROM sys.dm_exec_requests
WHERE blocking_session_id > 0;
Analyze the results to identify the blocking session and the session(s) being blocked.
Once you have identified the blocking session, gather more details about it using the sys.dm_exec_sessions
view. Execute the following query, replacing
with the actual identifier:
SELECT *
FROM sys.dm_exec_sessions
WHERE session_id =
This query will provide information about the blocking session, including login details and execution context.
To gain a deeper understanding of the resources being locked and the associated locks, utilize the sys.dm_tran_locks
view. Use the following query to select locks related to the blocking session:
SELECT *
FROM sys.dm_tran_locks
WHERE request_session_id =
This query will return information regarding the resources and locks associated with the blocking session.
Query execution plans can shed light on the cause of blocking by identifying expensive queries or missing indexes. Follow these steps:
Capture the query plan of the blocking session using the query:
SELECT *
FROM sys.dm_exec_query_stats AS qs
CROSS APPLY sys.dm_exec_query_plan (qs.plan_handle) AS qp
WHERE qs.session_id =
Analyze the execution plan for any inefficiencies, such as long-running queries or table scans. Consider optimizing these queries or adding missing indexes.
To resolve blocking, consider the following approaches:
Kill the blocking session using the KILL
statement. Execute the query:
KILL
Note: Killing a session forcefully may lead to data inconsistencies, so use this option with caution.
Identify and resolve the root cause of blocking. This may involve optimizing queries, redesigning data models, or restructuring transactional logic.
Implement appropriate isolation levels and locking hints in your queries to minimize blocking scenarios.
Consider implementing read replicas to offload read workloads and reduce contention.
Detecting and resolving blocking sessions is crucial for maintaining optimal performance in Azure SQL Solutions. By monitoring blocked sessions, gathering detailed information, analyzing execution plans, and applying appropriate resolution strategies, you can mitigate and prevent blocking issues. Strengthen your knowledge and skills in identifying sessions that cause blocking to excel in the Examining Administering Microsoft Azure SQL Solutions exam.
a) Read-only transactions
b) Long-running queries
c) Locking large tables
d) All of the above
Correct answer: d) All of the above
Correct answer: False
a) Blocking session
b) Deadlock victim
c) Locking session
d) Deadlock initiator
Correct answer: a) Blocking session
a) Use READ COMMITTED isolation level
b) Remove unnecessary indexes
c) Optimize query execution plans
d) All of the above
Correct answer: d) All of the above
Correct answer: True
a) READ COMMITTED
b) READ UNCOMMITTED
c) REPEATABLE READ
d) SERIALIZABLE
Correct answer: a) READ COMMITTED
a) Blocking can occur between sessions from different databases within the same server.
b) Blocking can only occur between sessions from the same database.
c) Blocking can only occur between sessions that are executing the same query.
d) Blocking can only occur between sessions from different Azure SQL Database servers.
Correct answer: a) Blocking can occur between sessions from different databases within the same server.
Correct answer: False
a) Shared locks
b) Exclusive locks
c) Update locks
d) All of the above
Correct answer: d) All of the above
a) sys.dm_tran_locks
b) sys.dm_exec_sessions
c) sys.dm_exec_requests
d) sys.dm_exec_connections
Correct answer: c) sys.dm_exec_requests
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