Sunday, February 22, 2009

Tuning SQL Statements

Top 10 worst SQL statements (measured by the time)

select top 10
SUBSTRING(st.text, (qs.statement_start_offset/2)+1,
((CASE qs.statement_end_offset
WHEN -1 THEN DATALENGTH(st.text)
ELSE qs.statement_end_offset
END - qs.statement_start_offset)/2) + 1) AS sql_text,
total_worker_time/execution_count "CPU per exec",
total_elapsed_time/execution_count/1000000 "Time per exec",
total_physical_reads/execution_count "Ph.Reads per exec",
total_logical_reads/execution_count "Log.Reads per exec",
total_logical_writes/execution_count "Log.Writes per exec"
FROM sys.dm_exec_query_stats AS qs
CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) AS st
where qs.total_elapsed_time/execution_count/1000000>10
order by "Time per exec" desc

Top 10 worst SQL statements with the explain plan

select top 10
qs.sql_handle,
total_worker_time/execution_count "CPU per exec",
total_elapsed_time/execution_count "Time per exec",
total_physical_reads/execution_count "Ph.Reads per exec",
total_logical_reads/execution_count "Log.Reads per exec",
total_logical_writes/execution_count "Log.Writes per exec",
qp.query_plan
from sys.dm_exec_query_stats as qs
cross apply sys.dm_exec_query_plan (qs.plan_handle) as qp

Indexes that are possibly not used

select * from sys.dm_db_index_usage_stats
where user_seeks=0 and user_scans=0 and user_lookups=0 and user_updates=0

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