Method and apparatus for accessing data as it existed at a previous point in time

摘要

Techniques are provided for sharing of flashback cursors by adding a time domain property to flashback cursors. This time domain property defines the range of flashback times for which the flashback cursor is valid. According to one embodiment, this "validity range" is closed at the lower bound and open at the upper bound. A subsequent flashback query can share an existing flashback cursor if the flashback time of the subsequent flashback query falls within the validity range of the existing flashback cursor. In one embodiment, the validity range of a flashback cursor is established based on times associated with indexes used to process the flashback query for which the flashback cursor was made. Consequently, an existing flashback cursor is less likely to be used by a subsequent flashback query when it would be inefficient to do so.