Enabling communication between database partitions using FCM communications

In a partitioned database environment, most communication between database partitions is handled by the fast communications manager (FCM).

To enable the FCM at a database partition and allow communication with other database partitions, you must create a service entry in the database partition's services file of the etc directory as shown later in this section. The FCM uses the specified port to communicate. If you have defined multiple database partitions on the same host, you must define a range of ports, as shown later in this section.

Before attempting to manually configure memory for the fast communications manager (FCM), it is recommended that you start with the automatic setting, which is also the default setting, for the number of FCM Buffers (fcm_num_buffers) and for the number of FCM Channels (fcm_num_channels). Use the system monitor data for FCM activity to determine if this setting is appropriate.

Windows Considerations

The TCP/IP port range is automatically added to the services file by:

The install program when it creates the instance or adds a new database partition
The db2icrt utility when it creates a new instance
The db2ncrt utility when it adds the first database partition on the computer

The syntax of a service entry is as follows:

   DB2_instance port/tcp #comment

DB2_instance: The value for instance is the name of the database manager instance. All characters in the name must be lowercase. Assuming an instance name of DB2PUSER, you specify DB2_db2puser.
port/tcp: The TCP/IP port that you want to reserve for the database partition.
#comment: Any comment that you want to associate with the entry. The comment must be preceded by a pound sign (#).

If the services file of the etc directory is shared, you must 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. When allocating ports, also ensure that you account for any processor that can be used as a backup.

If the services file of the etc directory is not shared, the same considerations apply, with one additional consideration: you must ensure that the entries defined for the Db2® database instance are the same in all services files of the etc directory (though other entries that do not apply to your partitioned database environment do not have to be the same).

If you have multiple database partitions on the same host in an instance, you must define more than one port for the FCM to use. To do this, include two lines in the services file of the etc directory to indicate the range of ports that you are allocating. The first line specifies the first port, and the second line indicates the end of the block of ports. In the following example, five ports are allocated for the SALES instance. This means no processor in the instance has more than five database partitions. For example:

   DB2_sales         9000/tcp
   DB2_sales_END     9004/tcp

Note: You must specify END in uppercase only. You must also ensure that you include both underscore (_) characters.