Github user jegonzal commented on the pull request:
https://github.com/apache/spark/pull/1217#issuecomment-47204112
@ankurdave and @rxin there is an issue with the current API. The
`sendMessage` function pull the active field out of the vertex value here:
https://github.com/apache/spark/pull/1217/files#diff-e399679417ffa6eeedf26a7630baca16R243
```scala
def sendMessageWrapper(triplet: EdgeTriplet[(VD, Boolean),ED]):
Iterator[(VertexId, A)] = {
val simpleTriplet = new EdgeTriplet[VD, ED]()
simpleTriplet.set(triplet)
simpleTriplet.srcAttr = triplet.srcAttr._1
simpleTriplet.dstAttr = triplet.dstAttr._1
val ctx = new EdgeContext(i, triplet.srcAttr._2, triplet.dstAttr._2)
sendMsg(simpleTriplet, ctx)
}
// Compute the messages for all the active vertices
val messages = g.mapReduceTriplets(sendMessageWrapper, mergeMsg,
Some((activeVertices, activeDirection)))
```
thereby allowing the user a simple `sendMsg` interface:
```scala
sendMsg: (EdgeTriplet[VD, ED], EdgeContext) => Iterator[(VertexId, A)]
```
However because we access the source and destination vertex attributes the
byte code inspection will force a full 3-way join even if the user doesn't
actually read the fields.
The simplest solution would be to change the send message interface to
operate on the extended vertex attribute passing (containing the active field).
```scala
sendMsg: (EdgeTriplet[(VD, Boolean), ED], EdgeContext) =>
Iterator[(VertexId, A)]
```
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