The PCTFREE Parameter

The PCTFREE parameter sets the minimum percentage of a data block to be reserved
as free space for possible updates to rows that already exist in that block. For example,
assume that you specify the following parameter within a CREATE TABLE statement:
PCTFREE 20
This states that 20% of each data block in this table’s data segment be kept free and
available for possible updates to the existing rows already within each block. New
rows can be added to the row data area, and corresponding information can be added
to the variable portions of the overhead area, until the row data and overhead total
80% of the total block size.

The PCTUSED Parameter

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. After a data block is
filled to the limit determined by PCTFREE, Oracle considers the block unavailable for

the insertion of new rows until the percentage of that block falls beneath the parameter
PCTUSED. Until this value is achieved, Oracle uses the free space of the data block only
for updates to rows already contained in the data block. For example, assume that you
specify the following parameter in a CREATE TABLE statement:
PCTUSED 40
In this case, a data block used for this table’s data segment is considered unavailable
for the insertion of any new rows until the amount of used space in the block falls to
39% or less (assuming that the block’s used space has previously reached PCTFREE).

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PCTFREE, PCTUSED

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