[jira] [Created] (TAJO-976) HashPartitioner doesn't make desired number of partitions infrequently.

["Hyoungjun Kim (JIRA)" <ji...@apache.org>]

Hyoungjun Kim created TAJO-976:
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             Summary: HashPartitioner doesn't make desired number of partitions infrequently.
                 Key: TAJO-976
                 URL: https://issues.apache.org/jira/browse/TAJO-976
             Project: Tajo
          Issue Type: Improvement
            Reporter: Hyoungjun Kim
            Assignee: Hyoungjun Kim
            Priority: Minor


If the number desired partition is a multiples of 31, HashPartitioner doesn't make desired number of partitions. I tested with the following code.
{code}
Random rand = new Random();
String[][] data = new String[1000][];

for (int i = 0; i < 1000; i++) {
  data[i] = new String[]{ String.valueOf(rand.nextInt(1000)), String.valueOf(rand.nextInt(1000)), String.valueOf(rand.nextInt(1000))};
}

int[] testNumPartitions = new int[]{31, 62, 124, 32, 63, 125};
for (int index = 0; index <  testNumPartitions.length; index++) {
  Set<Integer> ids = new TreeSet<Integer>();
  for (int i = 0; i < data.length; i++) {
    VTuple vtuple = new VTuple(new Datum[]{new TextDatum(data[i][0]), new TextDatum(data[i][1]), new TextDatum(data[i][2])});

    int hashValue = vtuple.hashCode();
    int partitionId = (hashValue & Integer.MAX_VALUE) % testNumPartitions[index];
    ids.add(partitionId);
  }

  System.out.println("Expected partition num: " + testNumPartitions[index] + ", real partition num:" + ids.size());
}
{code}
{noformat}
Expected partition num: 31, real partition num:10
Expected partition num: 62, real partition num:20
Expected partition num: 124, real partition num:40
Expected partition num: 32, real partition num:32
Expected partition num: 63, real partition num:63
Expected partition num: 125, real partition num:125
{noformat}



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