presto-main/src/main/java/io/prestosql/sql/planner/SystemPartitioningHandle.java/SystemPartitionFunction/HashBucketFunction
class SystemPartitionFunction:            public HashBucketFunction(HashGenerator generator, int bucketCount)
            {
                checkArgument(bucketCount > 0, "partitionCount must be at least 1");
                this.generator = generator;
                this.bucketCount = bucketCount;
            }