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SQL Server 2008 Query Performance Tuning Distilled by Grant Fritchey, Sajal Dam

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Chapter 6. Bookmark Lookup Analysis

To maximize the benefit from nonclustered indexes, you must minimize the cost of the data retrieval as much as possible. A major overhead associated with nonclustered indexes is the cost of excessive key lookups, commonly known as bookmark lookups, which are a mechanism to navigate from a nonclustered index row to the corresponding data row in the clustered index or the base table. Therefore, it makes sense to look at the cause of bookmark lookups and to evaluate how to avoid this cost.

In this chapter, I cover the following topics:

  • The purpose of bookmark lookups

  • Drawbacks of using bookmark lookups

  • Analysis of the cause of bookmark lookups

  • Techniques to resolve bookmark lookups

Purpose of Bookmark Lookups

When a SQL ...

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