IBM 000-8697 Manual Do Utilizador

System Architecture

The last available entry slot in the user table is always reserved for a
tbmonitor

process, regardless of whether any other tbmonitor processes are

currently running.

The number of entries in the user table is equal to the maximum number of
users permitted on this OnLine system, specified as

USERS

 in the configu-

ration file. If an additional user process attempts to attach to shared memory,
an error is returned.

Each entry in the user table occupies 102 bytes.

The upper limit for the maximum number of users (specified as

USERS

in the

configuration file) is 1000. The lower boundary for the value of

USERS

 is the

number of page cleaners (specified as

CLEANERS

 in the configuration file)

plus 4, plus 1 if mirroring is enabled. The four minimum user entries are
reserved for tbinit, tbundo, tbmonitor, and an entry for an administrative
user.

The OnLine buffer pool contains two types of buffers:

■

Regular buffers

■

Big buffers

If data pages are modified, entries are made in two other shared-memory
buffers that function solely to ensure the physical and logical consistency of
OnLine data:

■

Physical log buffer

■

Logical log buffer

The functions of the physical and logical log buffers are described on

 and

, respectively.