headConfig.setInputComparator(comparator, 0);
headConfig.setInputLocalStrategy(0, LocalStrategy.NONE);
headConfig.setIterationHeadPartialSolutionOrWorksetInputIndex(0);
// regular plan input (second input to the join)
headConfig.addInputToGroup(1);
headConfig.setInputSerializer(serializer, 1);
headConfig.setInputComparator(comparator, 1);
headConfig.setInputLocalStrategy(1, LocalStrategy.NONE);
headConfig.setInputCached(1, true);
headConfig.setRelativeInputMaterializationMemory(1, MEM_FRAC_PER_CONSUMER);