Topic: db scattered read

All hello!
There is a problem request to , causing it is a lot of disk readings,
Including full scan one rather big label,
As a whole it is clear that it is necessary to repair the plan, and to check up usage of indexes, statistics urgency... And still
In passing there was an a bit theoretical question on that,
As in similar situations to estimate the contribution in db scattered read
- Readings-records in-from temporal () ;
- The operations connected with  of the size PGA;
- Still any operations which can accompany negatively...?