Joseph E. Gonzalez created SPARK-3650:
-----------------------------------------
Summary: Triangle Count handles reverse edges incorrectly
Key: SPARK-3650
URL: https://issues.apache.org/jira/browse/SPARK-3650
Project: Spark
Issue Type: Bug
Components: GraphX
Affects Versions: 1.1.0
Reporter: Joseph E. Gonzalez
The triangle count implementation assumes that edges are aligned in a canonical
direction. As stated in the documentation:
```
Note that the input graph should have its edges in canonical direction
* (i.e. the `sourceId` less than `destId`)
```
However the TriangleCount algorithm does not verify that this condition holds
and indeed even the unit tests exploits this functionality:
~~~
val triangles = Array(0L -> 1L, 1L -> 2L, 2L -> 0L) ++
Array(0L -> -1L, -1L -> -2L, -2L -> 0L)
val rawEdges = sc.parallelize(triangles, 2)
val graph = Graph.fromEdgeTuples(rawEdges, true).cache()
val triangleCount = graph.triangleCount()
val verts = triangleCount.vertices
verts.collect().foreach { case (vid, count) =>
if (vid == 0) {
assert(count === 4) // <-- Should be 2
} else {
assert(count === 2) // <-- Should be 1
}
}
~~~
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