Sql Server tips and tricks
This is part of a series of quick tips and tricks I have accumulated over the year, that I think can be useful for others.
If you have similar short tips and tricks please leave a comment.
Most intensive queries
Most of us working with databases will at some point get task where we need to find out why the database is not performing as we expect and when running a big system that has intensive database usage it can be very tricky to find out what the cause is.
The query below is using the System dynamic Management View dm_exec_query_stats to list the performance statistics for the cached query plans in the Sql Server.
The scripts will provide you with some hints to which queries are the most CPU intensive.
SELECT 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 [Text],
qs.execution_count,
qs.total_logical_reads, qs.last_logical_reads,
qs.total_logical_writes, qs.last_logical_writes,
qs.total_worker_time,
qs.last_worker_time,
-- converting microseconds to seconds
qs.total_elapsed_time/1000000 total_elapsed_time_in_S,
qs.last_elapsed_time/1000000 last_elapsed_time_in_S,
qs.last_execution_time,
qp.query_plan
FROM sys.dm_exec_query_stats qs
-- Retrieve the query text
CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) qt
-- Retrieve the query plan
CROSS APPLY sys.dm_exec_query_plan(qs.plan_handle) qp
ORDER BY qs.total_worker_time DESC -- CPU time
SELECT TOP 50
[Avg. MultiCore/CPU time(sec)] = qs.total_worker_time / 1000000 / qs.execution_count,
[Total MultiCore/CPU time(sec)] = qs.total_worker_time / 1000000,
[Avg. Elapsed Time(sec)] = qs.total_elapsed_time / 1000000 / qs.execution_count,
[Total Elapsed Time(sec)] = qs.total_elapsed_time / 1000000,
qs.execution_count,
[Avg. I/O] = (total_logical_reads + total_logical_writes) / qs.execution_count,
[Total I/O] = total_logical_reads + total_logical_writes,
Query = 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
),
Batch = qt.[text],
[DB] = DB_NAME(qt.[dbid]),
qs.last_execution_time,
qp.query_plan
FROM sys.dm_exec_query_stats AS qs
CROSS APPLY sys.dm_exec_sql_text(qs.[sql_handle]) AS qt
CROSS APPLY sys.dm_exec_query_plan(qs.plan_handle) AS qp
WHERE qs.execution_count > 5 --more than 5 occurences
ORDER BY [Total MultiCore/CPU time(sec)] DESC
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