DB2 for Linux on iSeries: Implementation Guide

8 DB2 UDB for Linux on iSeries: Implementation Guide

2.1 Tutorial for a basic understanding of DB2 for Linux

In this section, we describe the minimum knowledge that is required to install and

configure DB2 UDB for Linux. Since DB2 UDB on Linux or UNIX or Windows

platforms has a different system structure than DB2 UDB for iSeries, those who

are not used to the structure, terms, should read this section first. If you are

familiar with DB2 on these platforms, that is DB2 UDB for Linux/UNIX/Windows

(LUW), you do not need to read this section.

For further information, refer to these DB2 manuals:

򐂰 IBM DB2 Universal Database Administration Guide: Planning, SC09-4822

򐂰 IBM DB2 Universal Database Administration Guide: Implementation,

SC09-4820

2.1.1 Database objects

For DB2 UDB for LUW, there is a nested structure that includes the data stored in

the database. We will discuss that here.

System

A system is usually a physical machine on which DB2 UDB is installed. In a

parallel database system, system means the set of machines which have all the

database partitions. A system can have multiple instances.

Instances

An instance (sometimes called a database manager) is the top level concept of

the structure. Databases have to be created in an instance. It controls what can

be done to the data, and manages system resources assigned to it. Each

instance is a complete environment. In a parallel database system, it contains all

the database partitions defined for a the parallel database system. An instance

has its own databases (which other instances cannot access), and all its

database partitions share the same system directories. It also has separate

security from other instances on the same machine (system). All the objects of

an instance are created under a directory which has the same name as the

instance name. The directory is the home directory of the instance owner and

called “instance directory”.

For DB2 UDB for iSeries, there is no concept of instance.

Databases

A relational database presents data as a collection of tables. A table consists of a

defined number of columns and any number of rows. Each database includes a

set of system catalog tables that describe the logical and physical structure of the

Chapter 2. Installation and configuration 9

data, a configuration file containing the parameter values allocated for the

database, and a recovery log with ongoing transactions and archival

transactions.

Figure 2-1 The structure of database objects

Database partition groups

A database partition group is a set of one or more database partitions. When you

want to create tables for the database, you first create the database partition

group where the table spaces will be stored, then you create the table space

where the tables will be stored. In a multi-partitioned database, a database can

have two or more database partitions in a database, which are in different

machines. Multi partitioned databases are out of the scope of this book.

In earlier versions of DB2, database partition groups were known as node

groups.

For DB2 UDB for iSeries, you can have database partition groups by installing

the DB2 Multisystem feature, which is an option of OS/400.

Table spaces

A database is organized into parts called table spaces. A table space is a place

to store tables. When creating a table, you can decide to have certain objects