Index: src/main/java/org/apache/hadoop/hbase/master/AssignmentManager.java =================================================================== --- src/main/java/org/apache/hadoop/hbase/master/AssignmentManager.java (revision 1553734) +++ src/main/java/org/apache/hadoop/hbase/master/AssignmentManager.java (working copy) @@ -1423,6 +1423,10 @@ RegionState state = addToRegionsInTransition(region, hijack); synchronized (state) { + if (!hijack && !state.isOffline()) { + // another thread beat us, just return + return; + } assign(region, state, setOfflineInZK, forceNewPlan, hijack); } }