presto-main/src/main/java/io/prestosql/operator/BucketPartitionFunction.java/BucketPartitionFunction/getPartition
class BucketPartitionFunction:    @Override
    public int getPartition(Page functionArguments, int position)
    {
        int bucket = bucketFunction.getBucket(functionArguments, position);
        return bucketToPartition[bucket];
    }