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SEEK is better then SCAN August 17, 2007

Posted by furrukhbaig in DMV's, dm_db_index_physical_stats, dm_db_index_usage_stats, Execution Plan, Index tuning, Index usefulness, Indexes, Optimize, Performance, Performance Tuning, Query hint, SEEK vs Scan, SQL Server 2005, SQL Server 2005 features, TSQL, XML Execution Plan.
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I have been involved in performance tuning for several databases and usually come across a situation where indexes has been created but due to poorly written SQL Code those indexes are not utilized or badly used by optimizer. To find out how optimizer using your index use query below. This will provide you the frequency optimizer is uses SEEK, SCAN and LOOKUP operation on indexes. 

As a rule of thumb SEEK is better then SCAN. But there are few scenarios where SCAN operator perform better then SEEK specially when large number of rows are expected to return by operation.

SELECT 
            Table_Name = OBJECT_NAME(usg.object_id),
            ind.name,
            usg.user_seeks,
            user_scans,
            user_lookups,
            last_user_seek,
            last_user_scan,
            last_user_lookup
FROM
            sys.dm_db_index_usage_stats usg
            INNER JOIN sys.indexes ind
                  ON usg.object_id = ind.object_id
                  AND usg.index_id = ind.index_id
WHERE
            — Your table list goes here
            OBJECT_NAME(usg.object_id) IN ( ‘Table_Name1’, ‘Table_Name2’ )
ORDER BY
            Table_Name       

  

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