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