23.5. Merging (MERGE2)

When a network error occurs, a cluster may be divided into several partitions. The JGroups MERGE service lets partitions communicate with each other and reform into a single cluster. Merging is configured in the MERGE2 sub-element in the JGroups Config element, like so:

<MERGE2 max_interval="10000"
    min_interval="2000"/>

The configurable attributes in the MERGE2 element are as follows.

max_interval: Specifies the maximum number of milliseconds between MERGE messages.
min_interval: Specifies the minimum number of milliseconds between MERGE messages.

JGroups selects a random value between min_interval and max_interval to send the MERGE message.

MERGE does not merge cluster states

Merging the application state maintained by the application using a channel must be done by the application. If MERGE2 is used in conjunction with TCPPING, the initial_hosts attribute must list all nodes to be merged. Only the listed nodes will be included in the merge process.

Alternatively, MPING can be used with TCP to provide multicast member discovery capabilities without needing to specify all nodes.