presto-main/src/main/java/io/prestosql/operator/HashBuilderOperator.java/HashBuilderOperator/spillIndex
class HashBuilderOperator:    private ListenableFuture<?> spillIndex()
    {
        checkState(!spiller.isPresent(), "Spiller already created");
        spiller = Optional.of(singleStreamSpillerFactory.create(
                index.getTypes(),
                operatorContext.getSpillContext().newLocalSpillContext(),
                operatorContext.newLocalSystemMemoryContext(HashBuilderOperator.class.getSimpleName())));
        return getSpiller().spill(index.getPages());
    }