Database Strategies: Using Informix XPS and DB2 Universal Database

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

keyword _END.

Be advised that these services ports are not used for client communication.

The database manager configuration parameter SVCENAME

defines the

service port where the DB2 listener is started, to listen for client

communications.