Re-organizing or rebuilding index would help the SQL optimizer to reduce the fragmentation for a better performance. In this case few users might have doubt that when to rebuild or reorganize (SQL Server 2005)? IN the series of Performance blog posts here I would like to suggest - How to Detect Table Fragmentation in SQL Server 2000 and 2005 article and IndexesTags related blog posts for index performance here. Further on this series you can run following TSQL with the help of DMV in SQL Server 2005:...(
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Read the complete post at http://sqlserver-qa.net/blogs/perftune/archive/2008/01/21/3208.aspx