JGroups Protocol MERGE2

External

• JGroups Manual http://www.jgroups.org/manual/html/protlist.html#MERGE2
• JGroups Wiki http://community.jboss.org/wiki/JGroupsMERGE2

Internal

• JGroups

Overview

If a group gets split for some reason (network partition), this protocol merges the subgroups back into one group. It run only by the coordinator. The FindSubgroupsTask of the MERGE2 protocol periodically sends a FIND_INITIAL_MBRS down the stack, which is handled by the implementation of the Discovery protocol (PING, MPING, etc) usually by sending a GET_MBRS_REQ message. More about this process here [[JGroups Protocol PING#Periodic_GET_MBRS_REQ_Requests][.

The FIND_INITIAL_MBRS events (and consequently GET_MBRS_REQ messages) are sent at random intervals between 'min_interval' and 'max_interval' milliseconds.

If another coordinator for the same group receives this message, it will initiate a merge process. The merge process does not merge state. The app has to handle the callback to merge state.

Configuration

  <MERGE2 max_interval="100000" min_interval="20000"/>

max_interval

If 'max_interval' is smaller or equal with 'min_interval', we get a configuration error:

21:14:16,436 ERROR [MERGE2] @main max_interval has to be greater than min_interval

and the stack won't start.