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System Architecture 2-95
Reserved Pages
Reserved Pages
The first 12 pages of the initial chunk of the root dbspace are reserved pages.
Copies of the first two reserved pages are also found on every other OnLine
chunk.
Each reserved page contains specific control and tracking information used
by tbinit. Below are listed the function of each of the 12 reserved pages. Each
reserved page is described, by field, in the pages that follow in this section.
Beginning with the third reserved page, PAGE_1CKPT, the pages are
organized into pairs. These pairs become important when tbinit begins to
update the reserved pages as part of the checkpoint procedure.
During every checkpoint, tbinit writes the system identification information
in shared memory to PAGE_PZERO, whether or not that information has
changed since the last checkpoint. Similarly, tbinit always overwrites
PAGE_CONFIG with the configuration file (specified as TBCONFIG).
Order Page Name Page Usage
1 PAGE_PZERO System identification
2 PAGE_CONFIG Copy of configuration file
3 PAGE_1CKPT Checkpoint / logical log tracking
4 PAGE_2CKPT Alternate CKPT page
5 PAGE_1DBSP Dbspace descriptions
6 PAGE_2DBSP Alternate DBSP page
7 PAGE_1PCHUNK Primary chunk descriptions
8 PAGE_2PCHUNK Alternate PCHUNK page
9 PAGE_1MCHUNK Mirror chunk descriptions
10 PAGE_2MCHUNK Alternate MCHUNK page
11 PAGE_1ARCH Archive tracking
12 PAGE_2ARCH Alternate ARCH page