High CPU usage in SQL Server

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Reasons for high CPU usage in SQL Server. Some common causes 



Inefficient queries: Queries that are poorly written or inefficient can consume a large amount of CPU resources.

Lack of indexes: If there are no indexes on the tables, SQL Server has to perform full table scans, which can be CPU-intensive.

Large data volumes: When working with large data volumes, SQL Server may need to use more CPU resources to process the data.

High concurrency: If there are a large number of users or connections executing queries concurrently, this can lead to high CPU usage.

Resource-intensive operations: Certain operations such as sorting, aggregating, or joining large data sets can consume significant CPU resources.

Server misconfiguration: Incorrectly configured settings, such as maximum degree of parallelism (MAXDOP), can cause excessive CPU usage.

Hardware limitations: If the server hardware is not sufficient to handle the workload, this can cause high CPU usage.

To find the SPID (Server Process ID) that is causing high CPU usage, you can use the following T-SQL query:


SELECT TOP 1 

  qs.total_worker_time / qs.execution_count AS avg_cpu_time,

  qs.execution_count,

  SUBSTRING(qt.text, (qs.statement_start_offset/2)+1, 

              ((CASE qs.statement_end_offset

                WHEN -1 THEN DATALENGTH(qt.text)

                ELSE qs.statement_end_offset

              END - qs.statement_start_offset)/2) + 1) AS query_text,

  er.session_id,

  er.status,

  er.cpu_time,

  er.total_elapsed_time,

  es.host_name,

  es.program_name,

  es.login_name,

  es.last_request_start_time,

  es.last_request_end_time

FROM 

  sys.dm_exec_query_stats AS qs

  CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) AS qt

  INNER JOIN sys.dm_exec_requests AS er ON qs.sql_handle = er.sql_handle

  INNER JOIN sys.dm_exec_sessions AS es ON er.session_id = es.session_id

WHERE 

  qs.total_worker_time > 0

  AND es.is_user_process = 1

ORDER BY 

  avg_cpu_time DESC;


The results are ordered by average CPU time per execution in descending order, and the top query is returned.


By using this query, you can identify the SPID that is consuming the most CPU resources, and then investigate further to determine the cause and take appropriate action.


To address high CPU usage, it is important to identify the cause and take appropriate action. This can include optimizing queries, creating indexes, adjusting server settings, or upgrading hardware resources. Regular monitoring and maintenance can also help prevent or mitigate high CPU usage.

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