Index Fragmentation

I was said that application is running slow so i need to make sure from the database point that it is working fine.
 When I check the fragmentation of index in all the table it  is fragmented by 80% or higher. But when I see the execution plan of some of the  query used by the application  there is  always index seek . Some of tables have 5 million rows and some has couple of hundreds of thousands .

So, my question  is Is it possible to use index seek  by the execution plan even though the index fragmentation is more than 80%. In such situation do I need to rebuild the indexes.
I haven't seen my maintenance plan for the index in the database in our system.

Could it possible that because of the index fragmentation  the application is being slow.


Thanks  in advance
manojbabaAsked:
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lcohanDatabase AnalystCommented:
manojbabaAuthor Commented:
Thanks Icohan,  

The link was  very informative but I really wanted to get answer to this part of the question

Is it possible to use index seek  by the execution plan even though the index fragmentation is more than 80%. In such situation do I need to rebuild the indexes.
TempDBACommented:
Are this plans that you are talking about are actual plan or estimated plans? Defragmenting the indexes will be useful. Just also check whether the indexes that you are talking about are what really is being used in the plan..
lcohanDatabase AnalystCommented:
"Is it possible to use index seek  by the execution plan even though the index fragmentation is more than 80%. In such situation do I need to rebuild the indexes."

Of course it is possible however the performance will suffer until you can rebuild the index. One issue may be if the index is clustered and there are gaps in keys then fragmentation may allways be there to some degree.
lcohanDatabase AnalystCommented:
And I know there are ways to DEFRAG an index however from my SQL experience that never had a signifficant positive impact like rebuild or recreate no matter how painful that may sound. In fact you could add a parrallel index with same composition different name and ONLINE=ON, do a UPDATE STATISTICS on that table and eventualy a SP_RECOMPILE table_name to flush old query plans using old index from cache, drop old and refres stats again.

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Microsoft SQL Server

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