The TableView schema object has several properties controlling performance parameters in virtual mode. In most cases, they can be left at their default values. However, you may want to try tuning them if you feel a need to improve performance.

Property	Description
VirtualSegmentSize	Number of rows fetched from the database and exposed to the user as a segment of the rowset. Default: 400. This is the minimum segment size. DataObjects for .NET can fetch more rows in a segment if necessary. That can happen if a grid with large number of rows is bound to the table view. With a bound grid, DataObjects for .NET always maintains the state where the first and last rows visible in the grid are on the "safe" distance from the ends of the current segment, the "safe distance" defined by the VirtualSyncThreshold property. Therefore, the segment size is always greater than the number of visible rows in the grid plus twice the threshold value.
VirtualSegmentCount	Maximum number of segments in the cache (only for DataAccessMode = Virtual).
VirtualSyncThreshold	Percent value from 0 to 100 (default: 12%). Determines the distance (number of rows) to the end of a segment that is considered a "danger zone", in the sense that the current segment must be changed to another segment (taken from the cache or fetched from the database) when the user positions on a row inside that zone. By default, it is 12% of 400 = 48 rows. See When a Virtual Table View Fetches Data Segments for details.
VirtualAsyncThreshold	Percent value from 0 to 100 (default: 30%). 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. See When a Virtual Table View Fetches Data Segments for details.