Donald K. Burleson Oracle Tips

Re-setting PCTUSED based on row length

It is very important that the DBA understand how the row length affects setting the values for PCTFREE and PCTUSED. You want to set PCTFREE such that room is left on each block for row expansion, and you want to set PCTUSED so that newly linked blocks have enough room to accept rows.

Here we see the tradeoff between effective space usage and performance. If you set PCTUSED to a high value, say 80, then a block will quickly become available to accept new rows, but it will not have room for a lot of rows before it becomes logically full again.

Remember the rule for PCTUSED. The lower the value for PCTUSED, the more space will be available on each data block, and subsequent INSERTs will run faster. The downside is that a block must be nearly empty before it becomes eligible to accept new rows.