Typically, you can configure DB2 Extended Enterprise Edition to have one database partition server assigned to each machine. There are situations, however, in which it would be advantageous to have several database partition servers running on the same machine. This means that the configuration can contain more logical nodes than machines. In these cases, the machine is said to be running multiple logical nodes if they participate in the same instance. If they participate in different instances, this machine is not running multiple logical nodes.
With multiple logical node support, you can choose from three types of configurations:
Configurations that use multiple logical nodes are useful when the system runs queries on a machine that has symmetric multiprocessor (SMP) architecture. The ability to configure multiple logical nodes on a machine is also useful if a machine fails. If a machine fails (causing the database partition server or servers on it to fail), you can restart the database partition server (or servers) on another machine, using the db2start command with the nodenum parameter. This ensures that user data remains available. Another benefit is that multiple logical nodes can exploit SMP hardware configurations. In addition, because database partitions are smaller, you can obtain better performance when performing such tasks as backing up and restoring database partitions and table spaces, and creating indexes.
The DB2NODE environment variable is used to route requests to a target logical node within a machine. This environment variable must be set in the session in which the application or command is issued and not in the DB2 profile registry. If this variable is not set, the target logical node defaults to the logical node which is defined with port 0 on the machine. For more information, see "Connecting to a Logical Node".
For more information about setting up logical nodes, see "Step 5. Create the Node Configuration File" (for AIX) or "Step 8. Create the Node Configuration File" (for Solaris), or refer to the Administration Guide.
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