JGroups Protocol MERGE2: Difference between revisions
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==Merging Process== | ==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 <tt>FindSubgroupsTask</tt> of the MERGE2 protocol periodically sends a FIND_INITIAL_MBRS 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) usually by sending a GET_MBRS_REQ message. More about this process here [[JGroups Protocol PING#Periodic_GET_MBRS_REQ_Requests|PING GET_MBRS_REQ Requests]]. | |||
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The FIND_INITIAL_MBRS events (and consequently GET_MBRS_REQ messages) are sent at random intervals between 'min_interval' and 'max_interval' milliseconds. | The FIND_INITIAL_MBRS events (and consequently GET_MBRS_REQ messages) are sent at random intervals between 'min_interval' and 'max_interval' milliseconds. | ||
Revision as of 06:00, 3 March 2016
External
- JGroups Manual http://www.jgroups.org/manual/html/protlist.html#MERGE2
- JGroups Wiki http://community.jboss.org/wiki/JGroupsMERGE2
Internal
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_INITIAL_MBRS down the stack, which is handled by the implementation of the Discovery protocol (PING, MPING, JDBC_PING, etc) 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.