@Override
  public Map<ServerName, List<RegionInfo>> getSnapShotOfAssignment(Collection<RegionInfo> regions) {
    AssignmentManager am = services.getAssignmentManager();
    return am != null ? am.getSnapShotOfAssignment(regions) : Collections.emptyMap();
  }
Use to add balancer decision history to ring-buffer
hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/MasterClusterInfoProvider.java