@Override
  public void unassign(RegionInfo regionInfo) throws IOException {
    AssignmentManager am = services.getAssignmentManager();
    if (am != null) {
      am.unassign(regionInfo);
    }
  }
Use to add balancer decision history to ring-buffer
hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/MasterClusterInfoProvider.java