presto-main/src/main/java/io/prestosql/operator/HashBuilderOperator.java/HashBuilderOperator/unspillLookupSourceIfRequested
class HashBuilderOperator:    private void unspillLookupSourceIfRequested()
    {
        checkState(state == State.INPUT_SPILLED);
        if (!spilledLookupSourceHandle.getUnspillingRequested().isDone()) {
            // Nothing to do yet.
            return;
        }

        verify(spiller.isPresent());
        verify(!unspillInProgress.isPresent());

        localUserMemoryContext.setBytes(getSpiller().getSpilledPagesInMemorySize() + index.getEstimatedSize().toBytes());
        unspillInProgress = Optional.of(getSpiller().getAllSpilledPages());

        state = State.INPUT_UNSPILLING;
    }