http://www.jboss.org/community/wiki/JBMCluster?decorator=print

anonymous wrote : Server Side Failover - It's good to have a buddy watch your 
back
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  | Every peer(node) has a buddy that will pick up all of it's messages if it 
fails.  If a server fails, the buddy will look in the database and recover all 
of it's buddies messages.  This only works for persistent messages.  From the 
docs - "If the node you are connected to fails, you will automatically fail 
over to another node and will not lose any persistent messages. You can carry 
on with your session seamlessly where you left off. Once and only once delivery 
of persistent messages is respected at all times."
  | 
  |  
  | 
  | There are two drawbacks to the buddy system.
  | 
  | 1.  Messages will be stranded if two buddies go down at the same time.
  | 
  | If two nodes go down that are buddies at the same time, one of the buddies 
messages will not be picked up.  For instance, if you have nodes 1, 2, and 3.  
If 3 is a failover node for 2 and 1 is a failovernode for 3, if 2 and 3 goe 
down, 2's messages will be lost, becuase 3 is not there to load 2's messages.  
The messages in Queue 2 will be stranded.
  | 
  | 2.  Clustered queues will only process messages from running nodes.
  | 
  | When running multiple nodes, the nodes need to be up at the same time to 
register with one another in the cluster.  If you bring the nodes up and down 
at different times, the messages will not roll over from node to node.  For 
example.  Bring node 1 up and process messages.  Bring node 1 down.  Bring node 
2 up and process messages.  You will notice that no messages have been pulled 
from node 1, until that node is brought up.  Even though the nodes hit the same 
database, they will only pull the messages for their own peer id, unless they 
are registered as a failover node for another peer and failover occurs.

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