What are PCTFREE and PCTUSED parameters?

What are PCTFREE and PCTUSED parameters?

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The PCTFREE parameter specifies the percentage of free space (the default value is ten) in each data block of a database object, which is reserved for future updates to the database object's rows. For example, if the PCTFREE parameter for a table is set to twenty, it indicates that twenty percent of each data block in the table will remain free and available for future updates to the table's rows.

Once a data block is full, i.e., it has only PCTFREE percent free space, Oracle stops inserting rows into it and removes it from the free list. Hence, if a large value is set for PCTFREE, the data blocks are more frequently removed from the free list, and vice versa. The data block is again added to the free list when the used space in it falls below the percent value set by the PCTUSED parameter (the default value is forty). Once the data block is added to the free list, Oracle again starts inserting new rows into it. Hence, if a large value is set for PCTUSED, the data blocks are more frequently returned to the free list and vice versa.

The sum of the PCTFREE and PCTUSED values cannot be more than one hundred.

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