[jira] [Created] (SPARK-2981) PartitionStrategy: VertexID hash overflow

["Larry Xiao (JIRA)" <ji...@apache.org>]

Larry Xiao created SPARK-2981:
---------------------------------

             Summary: PartitionStrategy: VertexID hash overflow
                 Key: SPARK-2981
                 URL: https://issues.apache.org/jira/browse/SPARK-2981
             Project: Spark
          Issue Type: Bug
          Components: GraphX
    Affects Versions: 1.0.2
            Reporter: Larry Xiao


In PartitionStrategy.scala a PartitionID is calculated by multiplying VertexId with a mixingPrime (1125899906842597L) then cast to Int, and mod numParts.

The Long is overflowed, and when cast to Int:

{quote}
scala> (1125899906842597L*1).toInt
res1: Int = -27

scala> (1125899906842597L*2).toInt
res2: Int = -54

scala> (1125899906842597L*3).toInt
res3: Int = -81
{quote}
As the cast produce number that are multiplies of 3, the partition is not useable when partitioning to multiples of 3.

for example when you partition to 6 or 9 parts:
{quote}
14/08/12 09:26:21 INFO GraphXPartition: GRAPHX: psrc Array((0,4347084), (1,0), (2,0), (3,3832578), (4,0), (5,0))
14/08/12 09:26:21 INFO GraphXPartition: GRAPHX: pdst Array((0,4347084), (1,0), (2,0), (3,3832578), (4,0), (5,0)) 

14/08/12 09:21:46 INFO GraphXPartition: GRAPHX: psrc Array((0,8179662), (1,0), (2,0), (3,0), (4,0), (5,0), (6,0), (7,0), (8,0))
14/08/12 09:21:46 INFO GraphXPartition: GRAPHX: pdst Array((0,8179662), (1,0), (2,0), (3,0), (4,0), (5,0), (6,0), (7,0), (8,0)) 
{quote}
I think solution is to cast after mod.
{quote}
scala> (1125899906842597L*3)
res4: Long = 3377699720527791

scala> (1125899906842597L*3) % 9
res5: Long = 3

scala> ((1125899906842597L*3) % 9).toInt
res5: Int = 3
{quote}



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