hama程序出现Messages must never be behind the vertex in ID问题解决

在运行hama程序时，在partition完成后，经常出现java.lang.IllegalArgumentException: Messages must never be behind the vertex in
ID! Current Message ID: 100003 vs. 100004。异常

看了一下hama源码，如下：

/**
* Iterating utility that ensures following things: <br/>
* - if vertex is active, but the given message does not match the vertexID,
* return null. <br/>
* - if vertex is inactive, but received a message that matches the ID, build
* an iterator that can be iterated until the next vertex has been reached
* (not buffer in memory) and set the vertex active <br/>
* - if vertex is active, and the given message does match the vertexID,
* return an iterator that can be iterated until the next vertex has been
* reached. <br/>
* - if vertex is inactive, and received no message, return null.
*/
@SuppressWarnings("unchecked")
private VertexMessageIterable<V, M> iterate(GraphJobMessage currentMessage,
V firstMessageId, Vertex<V, E, M> vertex,
BSPPeer<Writable, Writable, Writable, Writable, GraphJobMessage> peer) {
int comparision = firstMessageId.compareTo(vertex.getVertexID());
if (conf.getBoolean("hama.check.missing.vertex", true)) {
if (comparision < 0) {
throw new IllegalArgumentException(
"Messages must never be behind the vertex in ID! Current Message ID: "
+ firstMessageId + " vs. " + vertex.getVertexID());
}
} else {
while (comparision < 0) {
VertexMessageIterable<V, M> messageIterable = new VertexMessageIterable<V, M>(currentMessage,
firstMessageId, peer);
currentMessage = messageIterable.getOverflowMessage();
firstMessageId = (V)currentMessage.getVertexId();
comparision = firstMessageId.compareTo(vertex.getVertexID());
}
}
if (comparision == 0) {
// vertex id matches with the vertex, return an iterator with newest
// message
return new VertexMessageIterable<V, M>(currentMessage,
vertex.getVertexID(), peer);
} else {
// return null
return null;
}
}
问题出在传递的消息没有找到对应的节点，是自己输入的文件格式有问题。Hama中如果使用Vertex类，则输入的默认格式是（点、边<起点
终点>）。与mapreduce类似，mapper类为文件的每一行调用一个map（）函数，Vertex类为每一个点调用一个compute（）函数。该点名作为一个peer的名字。所以在边的输入文件里的<起点
终点>也要在点的位置出现，如果没有出现就会出现上面的错误。举个例子：如果输入文件如下就会出错（边只写终点）：

1 2 3 17

2 1

3 1

图形结构如下



17在边的位置出现了，但在点的位置没有出现。消息传递不到17的点，所以抛出异常。输入文件改为

1 2 3 17

2 1

3 1

17 1

就可以正常运行了。