presto-main/src/main/java/io/prestosql/operator/MergeHashSort.java/MergeHashSort/createHashGenerator
class MergeHashSort:    private static InterpretedHashGenerator createHashGenerator(List<Type> keyTypes)
    {
        int[] hashChannels = new int[keyTypes.size()];
        for (int i = 0; i < keyTypes.size(); i++) {
            hashChannels[i] = i;
        }
        return new InterpretedHashGenerator(keyTypes, hashChannels);
    }