derby.storage.initialPages

The derby.storage.initialPages property creates a Derby table or index with a number of pages already pre-allocated.

The on-disk size of a Derby table grows by one page at a time until eight pages of user data (or nine pages of total disk use; one is used for overhead) have been allocated. Then it will grow by eight pages at a time if possible.

To pre-allocate pages, specify the property prior to the CREATE TABLE or CREATE INDEX statement. The property value defines the number of user pages the table or index is to be created with. The purpose of this property is to preallocate a table or index of reasonable size if the user expects that a large amount of data will be inserted into the table or index. A table or index that has the pre-allocated pages will enjoy a small performance improvement over a table or index that has no pre-allocated pages when the data are loaded.

The total desired size of the table or index should be the following number of bytes:

(1 + derby.storage.initialPages) * derby.storage.pageSize

When you create a table or an index after setting this property, Derby attempts to preallocate the requested number of user pages. However, the operations do not fail even if they are unable to preallocate the requested number of pages, as long as they allocate at least one page.

Default

1 page.

Minimum value

The minimum number of initialPages is 1.

Maximum value

The maximum number of initialPages is 1000.

Example

-- system-wide property 
derby.storage.initialPages=30

-- database-wide property 
CALL SYSCS_UTIL.SYSCS_SET_DATABASE_PROPERTY( 
'derby.storage.initialPages', '30')

Dynamic or static

This property is static; if you change it while Derby is running, the change does not take effect until you reboot.