joshelser commented on issue #295: ACCUMULO-4662 Fixed queued work key in 
replication
URL: https://github.com/apache/accumulo/pull/295#issuecomment-326625242
 
 
   This part of the code is meant to handle the case when the active master 
changes while there data out to be replicated. The Master should initialize 
itself with the current state of ZooKeeper to know what has already been 
assigned out for replication (by the previous active Master).
   
   I can see that this bug would result in the Master holding onto some memory 
that it would never free (in the Map), and it would result in the Master trying 
to submit it back out to the cluster. However, I think eventually the Master 
(or TabletServer which took the work task) would see that there is no more work 
to be done and eventually clean up the record.
   
   I believe, by nature of the DistributedWorkQueue, there is sufficient 
exclusion to prevent two TabletServers from concurrently trying to replicate 
the same WAL. However, I believe the worst case would be that we inadvertently 
replicate the entire WAL twice.
   
   Would be nice to add a test for this method and not commit as-is.
 
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