Suppose I have a relation Grades(student_id, assignment_id, score). I have 150 students and 20 assignments. I would grade all submissions of one assignment based on the submission order, and then insert the records. As a result, based on my insertion nature, this relation is not sorted on student_id, but sorted on the assignment_id. I choose heap file as my file organization. My page is quite small it can only store 20 records, or 200 bytes in one page. The SearchKeySize is 4 bytes and PointerSize is 2 bytes. My buffer size is also small, 5 pages.

Suppose at the end of the semester, I need to curve the grades. I decide to increase all scores by 5 points. What is the I/O cost for this operation? Will my index on student_id be helpful in reducing I/O cost for this operation?