Instance or Database Manager

DB2 Instance or Database Manager

1. An Instance is also called as database Manager as it manages all the database within it.
2. It has it own 
1. processes 
2. configuration file
3. diagnostic log files.
3. A log file "db2diag.log" per instance is generated. It location is specified by the dbm cfg file parameter "Diagnostic data directory path               (DIAGPATH)"
4. Depth of logging Level in "db2diag.log" is specified by the dbm cfg file parameter "Diagnostic error capture level              (DIAGLEVEL) ", by default its level is set to 3.
5. Following are the five levels of diagnostic log: -
1. No diagnostic messages captured (not recommended)
2. Severe errors only
3. All errors
4. All errors and warnings (default)
5. All errors and warnings and informational messages
6. Following are the List of commands for Creating, Managing and Dropping  Instance.(Note:- All commands are executed at windows level command prompt)

1. db2icrt
1. Create a DB2® instance, including a DB2 pureScale® instance.
2. db2idrop
1. Removes a DB2® instance that was created by db2icrt.
3. db2ilist
1. Lists all the instances that are created using the db2icrt command
4. db2imigr(db2iupgrade in 10.1 version)
1. The db2iupgrade command upgrades an instance from a DB2 copy of a previous release to a DB2 copy of the current release.
5. db2iupdt
1. The db2iupdt command can be used to update an instance to a higher level within a release
6. db2start
1. To start an instance
7. db2stop
1. To stop an instance
8. db2iauto
1. Enables or disables the autostart of an instance after each system restart. This command is available on Linux and UNIX operating systems only
9. db2instance
1. The db2instance command is used to query the state of a DB2® instance
10. db2iprune
1. The db2iprune command can reduce the size of your DB2® product installation image before installation.
11. db2isetup
1. Starts the DB2 Instance Setup wizard, which is a graphical user interface (GUI) tool for creating, configuring, and extending instances.

DB2 Architecture

DB2 Environment has three layered Hierarchy

1. Physical Server Machine
1. Workstation on which database is installed forms the highest element in this hierarchy.It an physical machine.
2.  Virtual Server Machine
1. An Virtual Server is created on the machine when we install the DB2 Setup. It is commonly know as DAS( DB2 Admin Server).
2. It is collection of Instances.
3. It runs as a Windows services which can be start or stop using services.msc console.
4. It can also be start or stop using command prompt as 
1. db2admin stop or
2. db2admin start commands
5. It is required for 
1. Network database discovery
2. Remote Administration
3. Tools Catalog task scheduling
3. DB2 Virtual Registry( DB2 Profile Registry)
1. Similar to the Windows registry, which is used to save windows related info/path into variables, DB2 Profile registry also save Environment related information into variables.
2. From the command prompt ""db2set" is used to view or change all the option
4. Database Instance or Database Manager (DBM)
1. Instance can be defined as collection of processes which are used by the user to access the database as well as collection of resources.(memory)
2. In a single installation of DB2, we can generate multiple Instances from installation files. 
3. Instance acts as an manager for all the database residing within it. 
4. It can be started or stopped using command "db2start" or "db2stop" command ( Note:- this command needs to be executed from the db2 prompt unlike the command prompt)
5. It consists of DB2 Database Manager Configuration File per instance.( DBM CFG)
6. DBM CFG can be accessed using the command "get dbm cfg"( Note:- this command needs to be executed from the db2 prompt unlike the command prompt)
7. Instance configuration file consists of
1. security plan
2. performance attributes
3. communication
8. There are four types of Instances
1. ESE
2. WSE
3. Standalone
4. Client
5. Database
1. Database can be defined as collection of tables and related objects.
2. Each database include
1. system catalog tables
2. database configuration file
3. recovery log
3. Similar to the Instance configuration file, each database consists of its own configuration file.(DB CFG)
4.  DB CFG can be accessed using command "get db cfg".( Note:- this command needs to be executed from the db2 prompt unlike the command prompt)