Step 3: Calculate allocation overhead and total pages


Allocation overhead

Each table and each index on a table has an object allocation map (OAM). The OAM is stored on pages allocated to the table or index. A single OAM page holds allocation mapping for between 2,000 and 63,750 data pages or index pages. In most cases, the number of OAM pages required is close to the minimum value. To calculate the number of OAM pages for the table, use:

Formula

Example

Number of reserved data pages / 63,750

=

Minimum OAM pages

750,000 / 63,750

=

      12

Number of reserved data pages / 2000

=

Maximum OAM pages

750,000 / 2000

=

    375


Total pages needed

Add the number of OAM pages to the earlier totals to determine the total number of pages required:

Formula

Example

Minimum

Maximum

Minimum

Maximum

Data pages

+

+

     750000

     750000

OAM pages

+

+

             12

           375

Total

     750012

     750375