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Database Systems

By Dennis E. Shasha and Philippe Bonnet, December 01, 2004

Databases bring two things to the application development party-transactional semantics and querying capabilities.
December, 2004: Database Systems

Figure 6: Scan versus nonclustered index when data is in memory. Access through a nonclustered index gives much better performance than scan until 10 percent of the tuples are selected, then scan and indexed access have similar performances. The reason is that the MySQL optimizer does not use indexes when accessing a table if selectivity is higher than 10 percent.



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