Chapter 3. Configuration 79
You should ensure that the number of ports allocated in the file is either greater
than or equal to the largest number of multiple database partitions in the
instance. The FCM port entries in the /etc/services file must be identical on all the
hosts where there is a database partition for that instance.
In Example 3-4 on page 78, a range of nine ports are set up for FCM
communications, implying that there cannot be more than nine database
partitions within a single node.
Communication with logical partitions on the same node is accomplished using
UNIX sockets by default. However, this behavior can be altered by setting the
registry variable DB2_FORCE_FCM_BP. Setting this variable forces FCM
memory buffers to be created in a separate shared memory segment so that
communication between FCM daemons of different logical partitions on the same
physical node occurs through shared memory. The amount of memory allocated
is largely dependent on the number of FCM buffers to be created, as specified by
the fcm_num_buffers database manager configuration parameter. A side effect
of setting this variable is to reduce the maximum size of database buffer pools,
particularly in 32-bit implementations.
3.4 Configuring the instance
This section provides an overview of the parameters that are used in configuring
a DB2 instance and addresses where it is different from XPS.
3.4.1 Page size(s)
A DB2 instance can use multiple page sizes for different database objects and
their associated bufferpools. Page size is associated with a table space. In many
cases there are inherent performance advantages to having multiple page sizes,
but the primary reason for having multiple page sizes is that a data row cannot
span pages with DB2. For example, if the table space created has a 4 KB page
size, any table/index that is created in that table space must have a row size of
Note: The service ports specified in the example must follow a specific syntax.
Each entry must be prefixed with DB2_ and the last entry must have the
Be advised that these services ports are not used for client communication.
The database manager configuration parameter SVCENAME
service port where the DB2 listener is started, to listen for client