the meaning of PCTFREE, PCTUSED

1. 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.

 

1. 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.

Rows are inserted up to 80% only, Because PCTFREE specifies that20% of the block must remain open for updates of existing rows. Updates to exisiting rows use the free space reserved in the block. No new rows can be inserted into the block until the amount of used space is 39% or less. After the amount of used space falls below 40%, new rows can again be inserted into this block. Rows are inserted up to 80% only, because PCTFREE specifies that 20% of the block must remain open for updates of existing rows. This cycle continues . . .