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I've got a couple of nonclustered indexes on tables that have rows inserted quite often. These indexes are currently around 90% fragmented, according to SQL Server. If I rebuild them, they go down to ~5% fragmentation but they quickly get back up to 90% in a couple of hours.

What's going on, why are my indexes so persistently fragmented, and do I need to worry about it?

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How big are the tables? If they're small then the fragmentation will be proportionally higher. – SuperCoolMoss Apr 18 '12 at 11:13
up vote 4 down vote accepted

Nonclustered indexes get fragmented whenever page splits occur; this happens mostly when inserting non-sequential data, i.e. not in index order (it happens occasionally when inserting in index order, too - but not nearly as often.)

Consider rebuilding them with 50% padding, i.e. all current pages will be left half-empty.

This gives you the time required to double the index before fragmentation becomes an issue again.

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