In addition to data, index, and LOB pages used for data storage, Adaptive Server uses other types of pages to manage storage, track space allocation, and locate database objects. The sysindexes table also stores pointers that are used during data access.
The pages that manage space allocation and the sysindexes pointers are used to:
Speed the process of finding objects in the database
Speed the process of allocating and deallocating space for objects.
Provide a means for Adaptive Server to allocate additional space for an object that is near the space already used by the object. This helps performance by reducing disk-head travel.
The following types of pages track the disk space use by database objects:
Global allocation map (GAM) pages contain allocation bitmaps for an entire database.
Allocation pages track space usage and objects within groups of 256 pages, or 1/2MB.
Object allocation map (OAM) pages contain information about the extents used for an object. Each table and index has at least one OAM page that tracks where pages for the object are stored in the database.
Control pages manage space allocation for partitioned tables. Each partition has one control page.