Table fragmentation occurs when rows are not stored contiguously, or when rows are split between multiple pages. These rows require additional page access and this reduces the performance of the database server.
The effect that fragmentation has on performance varies. A table might be highly fragmented, but if it fits in memory, and the way it is accessed allows the pages to be cached, then the impact may be minimal. However, a fragmented table may cause much more I/O to be done and can significantly reduce performance if split rows are accessed frequently and the cost of extra I/Os is not reduced by caching.
While reorganizing tables and rebuilding a database can reduce fragmentation, doing so too frequently or not frequently enough, can also impact performance. Experiment using the tools and methods described in the following section to determine an acceptable level of fragmentation for your tables.
If you reduce fragmentation and performance is still poor, another issue may be to blame, such as inaccurate statistics. See Improving database performance.
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