IBM 000-8697 Manual Do Utilizador

IBM Informix OnLine Database Server Administrator’s Guide

After tbinit finishes computing the configuration values, it forks a child
process, which becomes the tbinit daemon. From this point on, the child
(daemon) process performs the initialization tasks. The parent process sleeps
until the child wakes it.

The tbinit daemon creates shared memory by acquiring the shared-memory
space from

UNIX

. The first segment size tbinit tries to acquire is the size of

shared memory, rounded up to the nearest multiple of 2 KB.

If tbinit cannot acquire a segment this large, it tries to acquire two shared-
memory segments that are each half the size of shared memory.

This “halve the size and double the number” tactic is repeated until tbinit
acquires enough segments to meet OnLine requirements.

Next, tbinit attaches the OnLine shared-memory segments to its virtual
address space. Refer to

 for a detailed explanation of how tbinit

finds and attaches to shared memory.

After attaching to shared memory, the tbinit daemon clears the shared-
memory space of uninitialized data. Then tbinit lays out the shared-memory
header information and initializes data in the shared-memory structures.
(For example, tbinit lays out the space needed for the logical log buffer and
then initializes and links together the three individual buffers that become
the logical log buffer.)

After shared-memory structures are initialized, the tbinit daemon begins
initializing the disk. It initializes all 12 reserved pages that are maintained in
the root dbspace on disk and writes

PAGE_PZERO

control information to the

disk. (Refer to

for further information about root dbspace reserved

pages.)