This property has effect only in virtual mode (when DataAccessMode is not Static). It is a performance tuning property. Do not change the default value unless you thoroughly understand the mechanics of virtual mode. The default value is 30%.

This property determines the distance (number of rows) to the end of a segment that is considered a 'preemptive fetch zone', in the sense that a new segment must be fetched from the database (if not found in the cache) when the user positions on a row inside that zone. By default, it is 30% of 400 = 120 rows.

Reference

TableView Class
TableView Members