PCTUSED and PCTFREE Parameters
The section on PCTUSED says, “The PCTUSED parameter sets the minimum percentage of a block that can be used for row data plus overhead before new rows are added to the block.”
I think this is wrong, or at least badly expressed. Consider part of the description of figure 2-5, “[A]fter the amount of used space falls below 40%, new rows can again be inserted into this block.” This makes me think that PCTUSED is a maximum, rather than a minimum. The idea is quite hard to express clearly in writing; I think the diagrams are much more useful here.
I always had trouble keeping PCTUSED and PCTFREE apart in my mind, until I read the best sentence in this section, “[U]pdates can reduce the available space of a block to less than PCTFREE, the space reserved for updates but not accesible to inserts.“
