derby.storage.pageReservedSpace

Function

Defines the percentage of space reserved for updates on an on-disk database page for tables only (not indexes); indicates the percentage of space to keep free on a page when inserting. Leaving reserved space on a page can minimize row overflow (and the associated performance hit) during updates. Once a page has been filled up to the reserved-space threshold, no new rows are allowed on the page. This reserved space is used only for rows that increase in size when updated, not for new inserts. Set this property prior to issuing the CREATE TABLE statement.

Regardless of the value of derby.storage.pageReservedSpace, an empty page always accepts at least one row.

Valid conglomerates

Tables only.

Default

20%.

Minimum value

The minimum value is 0% and the maximum is 100%. If you specify a value outside this range, Derby uses the default value of 20%.

Example

-- modifying the default for the system
derby.storage.pageReservedSpace=40
-- modifying the default for the database
CALL SYSCS_UTIL.SYSCS_SET_DATABASE_PROPERTY(
    'derby.storage.pageReservedSpace',
    '40')

Dynamic or static

This property is dynamic: if you change it while Derby is running, the change takes effect immediately. For information about dynamic changes to properties, see Dynamic and static properties.