Question

if anyone can break the query up into logical parts; it will be of great help. just a short note and pointers on what each part is doing ..

SELECT qs.execution_count AS [Runs], 
                     (qs.total_worker_time - qs.last_worker_time) / (qs.execution_count - 1) AS [Avg time],
                     qs.last_worker_time AS [Last time], 
                     (qs.last_worker_time - ((qs.total_worker_time - qs.last_worker_time) /
                     (qs.execution_count - 1))) AS [Time Deviation], 
                     CASE WHEN qs.last_worker_time = 0 
                          THEN 100
                          ELSE (qs.last_worker_time - ((qs.total_worker_time -
                                qs.last_worker_time) / (qs.execution_count - 1))) * 100
                     END
                     / (((qs.total_worker_time - qs.last_worker_time) /
                         (qs.execution_count - 1.0))) AS [% Time Deviation],
                     qs.last_logical_reads + qs.last_logical_writes + qs.last_physical_reads AS [Last IO],
                     ((qs.total_logical_reads + qs.total_logical_writes + qs.total_physical_reads) -
                     (qs.last_logical_reads + last_logical_writes + qs.last_physical_reads)) / 
                     (qs.execution_count - 1) AS [Avg IO], 
                     SUBSTRING (qt.text,(qs.statement_start_offset/2) + 1,
                               ((CASE WHEN qs.statement_end_offset = -1
                               THEN LEN(CONVERT(NVARCHAR(MAX), qt.text)) * 2
                               ELSE qs.statement_end_offset
                               END - qs.statement_start_offset)/2) + 1) AS [Individual Query], 
                    qt.text AS [Parent Query], 
                    DB_NAME(qt.dbid) AS [DatabaseName]
              INTO #SlowQueries
              FROM sys.dm_exec_query_stats qs
              CROSS APPLY sys.dm_exec_sql_text(qs.plan_handle) qt
              WHERE qs.execution_count > 1
              AND qs.total_worker_time != qs.last_worker_time
              ORDER BY [% Time Deviation] DESC

              SELECT [Runs], [Avg time], [Last time], [Time Deviation], [% Time Deviation], 
                     [Last IO], [Avg IO], [Last IO] - [Avg IO] AS [IO Deviation], 
                     CASE WHEN [Avg IO] = 0
                          THEN 0
                          ELSE ([Last IO]- [Avg IO]) * 100 / [Avg IO]
                     END AS [% IO Deviation], 
                     [Individual Query], [Parent Query], [DatabaseName]
             INTO #SlowQueriesByIO
             FROM #SlowQueries
             ORDER BY [% Time Deviation] DESC

            SELECT [Runs], [Avg time], [Last time], [Time Deviation], [% Time Deviation], [Last IO],
                   [Avg IO], [IO Deviation], [% IO Deviation], 
                   [Impedance] = [% Time Deviation] - [% IO Deviation], [Individual Query], [Parent Query],
                   [DatabaseName]
            FROM #SlowQueriesByIO
            WHERE [% Time Deviation] - [% IO Deviation] > 20
            ORDER BY [Impedance] DESC
            DROP TABLE #SlowQueries
            DROP TABLE #SlowQueriesByIO

Can anyone please help me understand the above query. Its simply too complex for me to understand. its a DMV of SQL server i found .

Answer 1

This explains it all:

http://www.sqlservercentral.com/articles/Performance+Tuning/63638/