An instance is a logical database manager environment
where you catalog databases and set configuration parameters. Depending
on your needs, you can create more than one instance on the same physical
server providing a unique database server environment for each instance.
Note: For non-root
installations on Linux and UNIX operating
systems, a single instance is created during the installation of your DB2® product. Additional instances
cannot be created.
Attention: Instances
cannot be shared across different DB2 versions.
You can use multiple instances to do the following:
- Use one instance for a development environment and another instance
for a production environment.
- Tune an instance for a particular environment.
- Restrict access to sensitive information.
- Control the assignment of SYSADM, SYSCTRL, and SYSMAINT authority
for each instance.
- Optimize the database manager configuration for each instance.
- Limit the impact of an instance failure. In the event of an instance
failure, only one instance is affected. Other instances can continue
to function normally.
Multiple instances will require:
- Additional system resources (virtual memory and disk space) for
each instance.
- More administration because of the additional instances to manage.
The instance directory stores all information that pertains to
a database instance. You cannot change the location of the instance
directory once it is created. The directory contains:
- The database manager configuration file
- The system database directory
- The node directory
- The node configuration file (db2nodes.cfg)
- Any other files that contain debugging information, such as the
exception or register dump or the call stack for the DB2 database processes.
Terminology:
- Bit-width
- The number of bits used to address virtual memory: 32-bit and
64-bit are the most common. This term might be used to refer to the
bit-width of an instance, application code, external routine code.
32-bit application means the same things as 32-bit width application.
- 32-bit DB2 instance
- A DB2 instance that contains
all 32-bit binaries including 32-bit shared libraries and executables.
- 64-bit DB2 instance
- A DB2 instance that contains
64-bit shared libraries and executables, and also all 32-bit client
application libraries (included for both client and server), and 32-bit
external routine support (included only on a server instance).