Index type and large I/O

When you specify an I/O size with prefetch, the specification can affect both the data pages and the leaf-level index pages. Table 3-1 shows the effects.

**Table 3-1: Access methods and prefetching**
Access method	Large I/O performed on
Table scan	Data pages
Clustered index	Data pages only, for allpages-locked tables Data pages and leaf-level index pages for data-only-locked tables
Nonclustered index	Data pages and leaf pages of nonclustered index

showplan reports the I/O size used for both data and leaf-level pages.

See “I/O Size Messages” on page 112 in the book Performance and Tuning: Monitoring and Analyzing for Performance for more information.