private static RelNode createBoxOperator(RelOptCluster cluster, RelNode eqRelNode) {
      String name = ".$box" + UNIQUE_IDENTIFIER.getAndIncrement();
      return new Box(cluster, name, eqRelNode);
    }
Rule that replaces Box operators by the plan they hold.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/views/HiveMaterializedViewBoxing.java