Fast communications manager (Linux and UNIX)

In multiple member environments, each member has a pair of FCM daemons to support communication between members that is related to agent requests. One daemon is for sending communications, and the other is for receiving. These daemons and supporting infrastructure are activated when an instance is started. FCM communication is also used for agents working within the same member; this type of communication is also known as intra-member communication.

The FCM daemon collects information about communication activities. You can obtain information about FCM communications by using the database system monitor. If communications fail between members or if they re-establish communications, the FCM daemons update monitor elements with this information. The FCM daemons also trigger the appropriate action for this event. An example of an appropriate action is the rollback of an affected transaction. You can use the database system monitor to help you set the FCM configuration parameters.

You can specify the number of FCM message buffers by using the fcm_num_buffers database manager configuration parameter. You can specify the number of FCM channels by using the fcm_num_channels database manager configuration parameter. By default, the fcm_num_buffers and fcm_num_channels database manager configuration parameters are set to AUTOMATIC. If the setting is AUTOMATIC, which is the recommended setting, the FCM monitors resource usage and adjusts resources to accommodate workload demand.