DB2 for Linux, UNIX and Windows Backup and Recovery – Introduction
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1 Backup and Recovery – Overview
The following chapter highlights some of the architectural components with respect to the backup and
recovery architecture. It explains the DB2 objects relevant for backups and the different methods of
backup, for example, offline backup or online backup. The chapter describes the DB2 backup
architecture and the DB2 logging. This information is aimed to enable you to develop and implement a
DB2 backup and recovery strategy.
1.1 Database Objects
DB2 databases are created in DB2 instances on the database server. A DB2 instance is also called
“database manager” as it provides the environment to host one or more databases. On one physical
server, multiple DB2 instances can be created. In an SAP environment each instance holds only one
database. While the database name or alias is determined by the SAP system ID (<SAPSID>) itself,
the DB2 instance is called db2<dbsid>.
Each database has multiple table spaces and a dedicated set of log files. You can mirror DB2 online
log files using database means. Each table space consists of one or more containers. Containers can
be directories, files or raw devices. The table space containers hold the database objects like tables
and indexes. Table spaces are a logical element with the table space containers as the physical
representation on disk. In a typical DB2 installation, the majority of the disk space is used by the table
space containers and log files. The DB2 instance and the database representation itself consist mainly
of configuration and administrative files in the respective directories.
The instance directory contains, for example, the database manager configuration files, the system
database directory, the node directory and the instance registry. It also holds the links to the installed
database software as well as some executables that are local to the instance.
The database directory contains the critical configuration files of the database. These files define, for
example, the buffer pools, table spaces, or the configuration of the database. The database directory
is also the location for the log file header as well as the history file.
In addition to the instance and database configuration, the DB2 system has a profile registry. Settings
in the DB2 profile registry can affect the instance (for example, parameters that are related to
communication) or the database (for example, parameters that are related to the behavior of the SQL
optimizer). In an SAP environment, one of these DB2 registry variables is ‘DB2_WORKLOAD’ which in
our case has the value ‘SAP’. Most of the parameters are set in the instance profile registry that is
stored in the instance directory. Some entries, however, are set for the database server. These
registry settings are set in the global registry which is stored in the file ‘/var/db2/global.reg’ in Linux,
UNIX environments. In Windows environments, the DB2 profile registry is stored in the Windows
registry (in the hive with key: HKEY_LOCAL_MACHINE\SOFTWARE\IBM\DB2\GLOBAL_PROFILE).
The following Figure 1-1 shows the simplified relationship between the different objects discussed.
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