JGroups Protocol MERGE2: Difference between revisions

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On the coordinator, the <tt>FindSubgroupsTask</tt> of the MERGE2 protocol periodically sends a FIND_ALL_VIEWS down the stack, which is handled by the implementation of the Discovery protocol ([[JGroups Protocol PING|PING]], [[JGroups Protocol MPING|MPING]], [[JGroups Protocol JDBC_PING|JDBC_PING]], etc). Upon receiving a FIND_ALL_VIEWS, the discovery protocol sends a GET_MBRS_REQ message  
On the coordinator, the <tt>FindSubgroupsTask</tt> of the MERGE2 protocol periodically sends a FIND_ALL_VIEWS down the stack, which is handled by the implementation of the Discovery protocol ([[JGroups Protocol PING|PING]], [[JGroups Protocol MPING|MPING]], [[JGroups Protocol JDBC_PING|JDBC_PING]], etc). Upon receiving a FIND_ALL_VIEWS, the discovery protocol sends a GET_MBRS_REQ message  
For more details on GET_MBRS_REQ requests handling by the Discovery protocols, see:
[[JGroups Protocol PING#Periodic_GET_MBRS_REQ_Requests|GET_MBRS_REQ requests handling by the Discovery protocols]]





Revision as of 06:12, 3 March 2016

External

Internal

Relevance

  • JGroups 3.4.3

Overview

MERGE2 merges split groups.

Merging Process

If a group splits, MERGE2 detects the split and re-joins the group.

Split situations:

  • A member is inactive (long GC), it is excluded from group, then comes back to life and it's part of an "older" view - the new view multicasted the coordinator does not include it.
  • Real network partitions that leads to two subgroups with two coordinators.

The merge protocol is run by coordinator.

On the coordinator, the FindSubgroupsTask of the MERGE2 protocol periodically sends a FIND_ALL_VIEWS down the stack, which is handled by the implementation of the Discovery protocol (PING, MPING, JDBC_PING, etc). Upon receiving a FIND_ALL_VIEWS, the discovery protocol sends a GET_MBRS_REQ message

For more details on GET_MBRS_REQ requests handling by the Discovery protocols, see:

GET_MBRS_REQ requests handling by the Discovery protocols


usually by sending a GET_MBRS_REQ message. More about this process here PING 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"/>

min_interval

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.

Also See

MERGE3