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The PCTFREE parameter specifies the percentage of

space in each data block that is reserved for growth

resulting from updates of rows in that data block. This

parameter has a default value of 10 percent.

For example, the value of the PCTFREE parameter is

specified as 20 in a CREATE TABLE statement. This

indicates that inserts to the block should stop as soon as

free space drops to 20 percent or less. The free space

thereafter can only be used for updates.

The PCTUSED parameter represents the minimum

percentage of the used space that the Oracle server tries

to maintain for each data block of the table. This

parameter has a default value of 40 percent.

When a data block is filled to the limit determined by the

value of the PCTFREE parameter, Oracle considers the

block unavailable for the insertion of new rows. The block

is unavailable for the insertion of new rows until the

percentage filled by the data of that block falls below the

value of the PCTUSED parameter.

Until the percentage of the block falls below the value of

the PCTUSED parameter, Oracle uses the free space of

the data block only for updating the rows contained in the

data block.

For example, if PCTUSED is defined as 40 percent, the

block is reused for inserts as soon as utilization drops to

less than 40 percent. Inserts continue until utilization

reaches 80 percent and the cycle repeats.