Tracking of Used and Free Pages
The DBMS space management handles used and free page tracking. A table uses a combination of a single free header page (H) and one or more free map pages (M) to track free and used pages.
Each free map page can track 16,000 pages, recording whether the page is free or used. As tables are allowed to grow past 16,000 pages, there can be more than one free map page in a table.
Free map pages are tracked by the free header page, whose location is recorded in the system catalog entries for the table.
Free header and free map pages are additional pages required for each table page count.
Note: All tables in the database can grow by a minimum of two pages. One free map page is added per 16,000 pages.
In VDBA, to view the graphical display of the pages, select a table and select the Pages tab.
Note: For B-tree tables, all empty disassociated data pages and any pages on the old free list are marked as “used.” The only way to reclaim this space is to select Shrink B-tree Index in the Modify Table Structure dialog in VDBA, or use the MODIFY TABLE TO BTREE statement in SQL. For more information, see the SQL Reference Guide.
Last modified date: 08/28/2024