Using I/O size N Kbtyes for data pages.
Using I/O size N Kbtyes for index leaf pages.
The messages report the I/O sizes used in the query. The possible sizes are 2K, 4K, 8K, and 16K.
If the table, index, LOB object, or database used in the query uses a data cache with large I/O pools, the optimizer can choose large I/O. It can choose to use one I/O size for reading index leaf pages, and a different size for data pages. The choice depends on the pool size available in the cache, the number of pages to be read, the cache bindings for the objects, and the cluster ratio for the table or index pages.
See Chapter 14, “Memory Use and Performance,” for more information on large I/O and the data cache.