Something in the way Moodle 2.x is storing grade histories stinks to high heaven. Below is the stats from our two system, having gone live with 2.3.x in February of this year and 2.5.1+ in August. The reason cited for removing grades from the grade tables when a user is unenrolled (causing no end of headaches) was to 'save space'. This doesn't seem to be saving space but eating it alive.
Moodle 1.9.x | Moodle 2.3 - 2.51 | |
terms | 2 year + 1 term | 2 terms plus summer sessions |
number of courses | 5,823 | 2,275 |
courses using gradebook | 1,681 | 611 |
number of grade_grades records | 667,070 | 278,870 |
grade_grades_history size | 315MB | 850MB |
number of grade_items records | 33,171 | 11,800 |
grade_items_history size | 1.8MB | 844MB |