Getting ready

An important component of FCM is the FCM buffer. An FCM buffer is actually a structure that holds data that is going to be passed between agents. The communication ports used by FCM are defined in the /etc/services file. For example, in our case, we have defined a maximum of four logical ports:

DB2_db2instp 60008/tcp
DB2_db2instp_1 60009/tcp
DB2_db2instp_2 60010/tcp
DB2_db2instp_END 60011/tcp

How to do it…

FCM is controlled by the following parameters:

Both parameters have AUTOMATIC svalues assigned by default.

How it works...

FCM buffers are 4 KB memory structures that are allocated in instance shared memory. Internally, they have assigned priority levels, according to the type of messages they are handling on (failure messages have a higher priority than row passing messages between partitions).

There's more...

To set up a proper value for a number of buffers, it is recommended to monitor, from time to time, the values assigned to FCM_NUM_BUFFERS and FCM_NUM_CHANNELS, running in the AUTOMATIC mode, especially when the processing is at peak values.

To monitor FCM buffers and channels, issue the following command:

[db2instp@nodedb21 ~]$ db2 "get snapshot for database manager" ………………………………………………………………………………………………………… Node FCM information corresponds to = 0 Free FCM buffers = 8049 Total FCM buffers = 8055 Free FCM buffers low water mark = 8037 Maximum number of FCM buffers = 1048940 Free FCM channels = 4475 Total FCM channels = 4475 Free FCM channels low water mark = 4464 Maximum number of FCM channels = 1048940 Number of FCM nodes = 5 ………………………………………………………………………………………………………………. 

See also

The Monitoring and configuring FCM for optimal performance recipe in Chapter 11, Connectivity and Networking.