PCTFEEE and PCTUSED
To describe the activities of a data block, imagine it is a cup. How much the waiter usually pours water into the cup? Say 90% full. At this point PCTFREE=10, which means when a block is 90% utilized, it can’t be used anymore – it will be removed from the FREELIST. The 10% free space is reserved for the potential space increase caused by the UPDATE statement. If the PCTFREE is too small, ROW CHAINING will happen.
PCTUSED stands for when the waiter can refill the cup. Say PCTUSED=40, means when there is 40% or less left in the cup, the waiter will refill the cup again for us. Now there is a trade-off between the waiter and the cup. Big PCTUSED means busy waiters (I/O) but well-utilized cups (Storage). Small PCTUSED means happy waiters but bad-utilized cups.
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