IBM 000-8697 User Manual

System Architecture

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

).

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