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Monday, January 12, 2015

Find Most Expensive Queries Using DMV


Find Most Expensive Queries Using Dynamic Management Views(DMV)

When you try to find out the performance of an sql server, this query will help us.
It records how many times that execution plan get re-used by following execution. This will give us the count of the execution. It records the number of logical reads, logical writes, elapsed time etc. all this counter will help to find poor performer while monitoring SQL Server queries.
The query will use the Dynamic Management Views. DMV returns server state information that can be used to monitor the health of the server instance, diagnose problems and performance.
Following is the query which finds out top 10 most expensive queries


SELECT TOP 10 SUBSTRING(qt.TEXT, (qstat.statement_start_offset/2)+1,

  ((CASE qstat.statement_end_offset

  WHEN -1 THEN DATALENGTH(qt.TEXT)

  ELSE qstat.statement_end_offset

  END - qstat.statement_start_offset)/2)+1),

  qstat.execution_count,

  qstat.total_logical_reads, qstat.last_logical_reads,

  qstat.total_logical_writes, qstat.last_logical_writes,

  qstat.total_worker_time,

  qstat.last_worker_time,

  qstat.total_elapsed_time/1000000 total_elapsed_time_in_S,

  qstat.last_elapsed_time/1000000 last_elapsed_time_in_S,

  qstat.last_execution_time,

  qplan.query_plan

FROM sys.dm_exec_query_stats  qstat

CROSS APPLY sys.dm_exec_query_plan(qstat.plan_handle) qplan

CROSS APPLY sys.dm_exec_sql_text(qstat.sql_handle)  qt

ORDER BY qstat.total_logical_reads DESC -- logical reads

-- ORDER BY qstat.total_logical_writes DESC -- logical writes

-- ORDER BY qstat.total_worker_time DESC -- CPU time

Happy Coding !!

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