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From edu...@apache.org
Subject [7/9] git commit: updated refs/heads/trunk to 8675c84
Date Mon, 08 Dec 2014 19:21:42 GMT
http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/instrumented/package-info.java
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diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/instrumented/package-info.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/instrumented/package-info.java
new file mode 100644
index 0000000..b50f00f
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/instrumented/package-info.java
@@ -0,0 +1,22 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Instrumentation results of the example Giraph programs.
+ */
+package org.apache.giraph.debugger.examples.instrumented;

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/BuggyConnectedComponentsComputation.java
----------------------------------------------------------------------
diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/BuggyConnectedComponentsComputation.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/BuggyConnectedComponentsComputation.java
new file mode 100644
index 0000000..1a83a0e
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/BuggyConnectedComponentsComputation.java
@@ -0,0 +1,99 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.giraph.debugger.examples.integrity;
+
+import java.io.IOException;
+
+import org.apache.giraph.edge.Edge;
+import org.apache.giraph.graph.BasicComputation;
+import org.apache.giraph.graph.Vertex;
+import org.apache.hadoop.io.LongWritable;
+import org.apache.hadoop.io.NullWritable;
+
+/**
+ * Implementation of the HCC algorithm that identifies connected components and
+ * assigns each vertex its "component identifier" (the smallest vertex id in the
+ * component)
+ *
+ * The idea behind the algorithm is very simple: propagate the smallest vertex
+ * id along the edges to all vertices of a connected component. The number of
+ * supersteps necessary is equal to the length of the maximum diameter of all
+ * components + 1
+ *
+ * The original Hadoop-based variant of this algorithm was proposed by Kang,
+ * Charalampos, Tsourakakis and Faloutsos in
+ * "PEGASUS: Mining Peta-Scale Graphs", 2010
+ *
+ * http://www.cs.cmu.edu/~ukang/papers/PegasusKAIS.pdf
+ */
+public class BuggyConnectedComponentsComputation extends
+  BasicComputation<LongWritable, LongWritable, NullWritable, LongWritable> {
+
+  /**
+   * Propagates the smallest vertex id to all neighbors. Will always choose to
+   * halt and only reactivate if a smaller id has been sent to it.
+   *
+   * @param vertex
+   *          Vertex
+   * @param messages
+   *          Iterator of messages from the previous superstep.
+   * @throws IOException
+   */
+  @Override
+  public void compute(Vertex<LongWritable, LongWritable, NullWritable> vertex,
+    Iterable<LongWritable> messages) throws IOException {
+    long currentComponent = vertex.getValue().get();
+
+    if (getSuperstep() == 0) {
+      vertex.setValue(vertex.getId());
+      for (Edge<LongWritable, NullWritable> edge : vertex.getEdges()) {
+        sendMessage(edge.getTargetVertexId(), vertex.getValue());
+      }
+      vertex.voteToHalt();
+      return;
+    }
+
+    boolean changed = false;
+    // did we get a smaller id ?
+    for (LongWritable message : messages) {
+      long candidateComponent = message.get();
+      // INTENTIONAL BUG: in the original algorithm the value of the comparison
+      // sign should be <.
+      // We note that this algorithm will end up finding the components
+      // correctly, but the ID of
+      // each component will be the minimum vertex ID in the component.
+      // In the original
+      // org.apache.giraph.examples.ConnectedComponentsComputation, the ID of
+      // each
+      // component is the maximum vertex ID in the component.
+      if (candidateComponent > currentComponent) {
+        currentComponent = candidateComponent;
+        changed = true;
+      }
+    }
+
+    // propagate new component id to the neighbors
+    if (changed) {
+      vertex.setValue(new LongWritable(currentComponent));
+      for (Edge<LongWritable, NullWritable> edge : vertex.getEdges()) {
+        sendMessage(edge.getTargetVertexId(), vertex.getValue());
+      }
+    }
+    vertex.voteToHalt();
+  }
+}

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/CCFindingMissingReverseEdgeMsgIntegrityDebugConfig.java
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diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/CCFindingMissingReverseEdgeMsgIntegrityDebugConfig.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/CCFindingMissingReverseEdgeMsgIntegrityDebugConfig.java
new file mode 100644
index 0000000..ea1e056
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/CCFindingMissingReverseEdgeMsgIntegrityDebugConfig.java
@@ -0,0 +1,47 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.giraph.debugger.examples.integrity;
+
+import org.apache.giraph.debugger.DebugConfig;
+import org.apache.hadoop.io.LongWritable;
+import org.apache.hadoop.io.NullWritable;
+
+/**
+ * Debug configuration file for ConnectedComponents, that is configured to check
+ * that in the second superstep, the value of a message sent from vertex u to v
+ * has to be greater than or equal to v's ID.
+ */
+public class CCFindingMissingReverseEdgeMsgIntegrityDebugConfig extends
+  DebugConfig<LongWritable, LongWritable, NullWritable, LongWritable,
+  LongWritable> {
+
+  @Override
+  public boolean shouldCheckMessageIntegrity() {
+    return true;
+  }
+
+  @Override
+  public boolean isMessageCorrect(LongWritable srcId, LongWritable dstId,
+    LongWritable message, long superstepNo) {
+    if (superstepNo == 1) {
+      return message.get() >= dstId.get();
+    } else {
+      return true;
+    }
+  }
+}

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/ConnectedComponentsDebugConfig.java
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diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/ConnectedComponentsDebugConfig.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/ConnectedComponentsDebugConfig.java
new file mode 100644
index 0000000..5bb490a
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/ConnectedComponentsDebugConfig.java
@@ -0,0 +1,55 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.giraph.debugger.examples.integrity;
+
+import org.apache.giraph.debugger.DebugConfig;
+import org.apache.hadoop.io.LongWritable;
+import org.apache.hadoop.io.NullWritable;
+
+/**
+ * Debug configuration file for ConnectedComponents, that is configured to check
+ * the integrity of the vertex values: The current check is that the vertex
+ * value is less than or equal to the id of the vertex.
+ */
+public class ConnectedComponentsDebugConfig extends
+  DebugConfig<LongWritable, LongWritable, NullWritable, LongWritable,
+  LongWritable> {
+
+  @Override
+  public boolean shouldCheckVertexValueIntegrity() {
+    return true;
+  }
+
+  @Override
+  public boolean isVertexValueCorrect(LongWritable vertexId,
+    LongWritable value) {
+    return value.get() <= vertexId.get();
+  }
+
+  @Override
+  public boolean shouldCheckMessageIntegrity() {
+    return true;
+  }
+
+  @Override
+  public boolean isMessageCorrect(LongWritable srcId, LongWritable dstId,
+    LongWritable message, long superstepNo) {
+    return message.get() <= srcId.get();
+  }
+
+}

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/ConnectedComponentsMsgIntegrityDebugConfig.java
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diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/ConnectedComponentsMsgIntegrityDebugConfig.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/ConnectedComponentsMsgIntegrityDebugConfig.java
new file mode 100644
index 0000000..61641a9
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/ConnectedComponentsMsgIntegrityDebugConfig.java
@@ -0,0 +1,54 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.giraph.debugger.examples.integrity;
+
+import org.apache.giraph.debugger.DebugConfig;
+import org.apache.giraph.graph.Vertex;
+import org.apache.hadoop.io.LongWritable;
+import org.apache.hadoop.io.NullWritable;
+
+/**
+ * Debug configuration file for ConnectedComponents, that is configured to check
+ * the integrity of the messages sent: The current check is that the message
+ * value is less than or equal to the id of the source vertex.
+ */
+public class ConnectedComponentsMsgIntegrityDebugConfig extends DebugConfig<
+  LongWritable, LongWritable, NullWritable, LongWritable, LongWritable> {
+
+  @Override
+  public boolean shouldCatchExceptions() {
+    return false;
+  }
+
+  @Override
+  public boolean shouldDebugVertex(
+    Vertex<LongWritable, LongWritable, NullWritable> vertex, long superstepNo) {
+    return false;
+  }
+
+  @Override
+  public boolean shouldCheckMessageIntegrity() {
+    return true;
+  }
+
+  @Override
+  public boolean isMessageCorrect(LongWritable srcId, LongWritable dstId,
+    LongWritable message, long superstepNo) {
+    return message.get() <= srcId.get();
+  }
+}

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/ConnectedComponentsRandomVerticesDebugConfig.java
----------------------------------------------------------------------
diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/ConnectedComponentsRandomVerticesDebugConfig.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/ConnectedComponentsRandomVerticesDebugConfig.java
new file mode 100644
index 0000000..f737739
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/ConnectedComponentsRandomVerticesDebugConfig.java
@@ -0,0 +1,38 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.giraph.debugger.examples.integrity;
+
+import org.apache.giraph.debugger.DebugConfig;
+import org.apache.hadoop.io.LongWritable;
+import org.apache.hadoop.io.NullWritable;
+
+/**
+ * Debug configuration file for ConnectedComponents, that is configured to
+ * capture a random set of 10 vertices.
+ */
+public class ConnectedComponentsRandomVerticesDebugConfig extends DebugConfig<
+  LongWritable, LongWritable, NullWritable, LongWritable, LongWritable> {
+
+  /**
+   * @return the number of random vertices that Graft should capture, which is
+   *         set to 10 in our case.
+   */
+  public int numberOfRandomVerticesToCapture() {
+    return 10;
+  }
+}

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/ConnectedComponentsVValueIntegrityDebugConfig.java
----------------------------------------------------------------------
diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/ConnectedComponentsVValueIntegrityDebugConfig.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/ConnectedComponentsVValueIntegrityDebugConfig.java
new file mode 100644
index 0000000..ff01276
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/ConnectedComponentsVValueIntegrityDebugConfig.java
@@ -0,0 +1,54 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.giraph.debugger.examples.integrity;
+
+import org.apache.giraph.debugger.DebugConfig;
+import org.apache.giraph.graph.Vertex;
+import org.apache.hadoop.io.LongWritable;
+import org.apache.hadoop.io.NullWritable;
+
+/**
+ * Debug configuration file for ConnectedComponents, that is configured to check
+ * the integrity of the vertex values: The current check is that the vertex
+ * value is less than or equal to the id of the vertex.
+ */
+public class ConnectedComponentsVValueIntegrityDebugConfig extends DebugConfig<
+  LongWritable, LongWritable, NullWritable, LongWritable, LongWritable> {
+
+  @Override
+  public boolean shouldCatchExceptions() {
+    return false;
+  }
+
+  @Override
+  public boolean shouldDebugVertex(
+    Vertex<LongWritable, LongWritable, NullWritable> vertex, long superstepNo) {
+    return false;
+  };
+
+  @Override
+  public boolean shouldCheckVertexValueIntegrity() {
+    return true;
+  }
+
+  @Override
+  public boolean isVertexValueCorrect(LongWritable vertexId, LongWritable
+    value) {
+    return value.get() <= vertexId.get();
+  }
+}

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/package-info.java
----------------------------------------------------------------------
diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/package-info.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/package-info.java
new file mode 100644
index 0000000..8b944af
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/integrity/package-info.java
@@ -0,0 +1,24 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * An example Giraph program to be debugged using Graft's integrity check
+ * functionality.
+ */
+package org.apache.giraph.debugger.examples.integrity;
+

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/MWMComputation.java
----------------------------------------------------------------------
diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/MWMComputation.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/MWMComputation.java
new file mode 100644
index 0000000..f212c66
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/MWMComputation.java
@@ -0,0 +1,111 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.giraph.debugger.examples.mwm;
+
+import java.io.IOException;
+
+import org.apache.giraph.edge.Edge;
+import org.apache.giraph.graph.BasicComputation;
+import org.apache.giraph.graph.Vertex;
+import org.apache.hadoop.io.DoubleWritable;
+import org.apache.hadoop.io.LongWritable;
+
+/**
+ * The implementation of an approximate maximum weight matching algorithm.
+ * Vertices pick their max-weight neighbors and if two vertices u and v pick
+ * each other, they are matched and removed from the graph. Edges
+ * pointing to u and v are also removed from the graph.
+ */
+public class MWMComputation extends
+  BasicComputation<LongWritable, VertexValue, DoubleWritable, LongWritable> {
+
+  @Override
+  public void compute(Vertex<LongWritable, VertexValue, DoubleWritable> vertex,
+    Iterable<LongWritable> messages) throws IOException {
+    if (getSuperstep() > 500) {
+      vertex.voteToHalt();
+    }
+    long phase = getSuperstep() % 2;
+    if (vertex.getValue().isMatched() || vertex.getNumEdges() == 0) {
+      vertex.voteToHalt();
+      return;
+    }
+    if (phase == 0) {
+      removeEdges(vertex, messages);
+      if (vertex.getNumEdges() == 0) {
+        vertex.voteToHalt();
+        return;
+      }
+      long maxValueVertexID = pickMaxValueVertex(vertex);
+      vertex.getValue().setMatchedID(maxValueVertexID);
+      vertex.setValue(vertex.getValue());
+      sendMessage(new LongWritable(maxValueVertexID), vertex.getId());
+    } else if (phase == 1) {
+      long matchedID = vertex.getValue().getMatchedID();
+      boolean isMatched = false;
+      for (LongWritable matchingVertexID : messages) {
+        if (matchingVertexID.get() == matchedID) {
+          isMatched = true;
+          break;
+        }
+      }
+      if (isMatched) {
+        vertex.getValue().setMatched(true);
+        vertex.setValue(vertex.getValue());
+        sendMessageToAllEdges(vertex, vertex.getId());
+        vertex.voteToHalt();
+      }
+    }
+  }
+
+  /**
+   * Remove edges.
+   *
+   * @param vertex the vertex
+   * @param messages the incoming messages
+   */
+  private void removeEdges(
+    Vertex<LongWritable, VertexValue, DoubleWritable> vertex,
+    Iterable<LongWritable> messages) {
+    for (LongWritable matchedNbr : messages) {
+      vertex.removeEdges(matchedNbr);
+    }
+  }
+
+  /**
+   * @param vertex the vertex
+   * @return the max id among neighbor vertices
+   */
+  private long pickMaxValueVertex(
+    Vertex<LongWritable, VertexValue, DoubleWritable> vertex) {
+    long maxWeightNbrID = -1;
+    double maxWeight = -1.0;
+    for (Edge<LongWritable, DoubleWritable> edge : vertex.getEdges()) {
+      if (maxWeightNbrID == -1) {
+        maxWeightNbrID = edge.getTargetVertexId().get();
+        maxWeight = edge.getValue().get();
+      } else {
+        if (edge.getValue().get() > maxWeight) {
+          maxWeightNbrID = edge.getTargetVertexId().get();
+          maxWeight = edge.getValue().get();
+        }
+      }
+    }
+    return maxWeightNbrID;
+  }
+}

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/MWMDebugConfig.java
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diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/MWMDebugConfig.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/MWMDebugConfig.java
new file mode 100644
index 0000000..863a1c7
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/MWMDebugConfig.java
@@ -0,0 +1,54 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.giraph.debugger.examples.mwm;
+
+import org.apache.giraph.debugger.DebugConfig;
+import org.apache.hadoop.io.DoubleWritable;
+import org.apache.hadoop.io.LongWritable;
+
+/**
+ * DebugConfig for max weight matching.
+ */
+public class MWMDebugConfig
+  extends
+  DebugConfig<LongWritable, VertexValue, DoubleWritable, LongWritable,
+  LongWritable> {
+
+  @Override
+  public boolean shouldCheckVertexValueIntegrity() {
+    return true;
+  }
+
+  @Override
+  public boolean isVertexValueCorrect(LongWritable vertexId,
+    VertexValue value) {
+    return value.getMatchedID() != vertexId.get();
+  }
+
+  @Override
+  public boolean shouldCheckMessageIntegrity() {
+    return true;
+  }
+
+  @Override
+  public boolean isMessageCorrect(LongWritable srcId, LongWritable dstId,
+    LongWritable message, long superstepNo) {
+    return message.get() == srcId.get();
+  }
+
+}

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/MWMMessageConstraintDebugConfig.java
----------------------------------------------------------------------
diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/MWMMessageConstraintDebugConfig.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/MWMMessageConstraintDebugConfig.java
new file mode 100644
index 0000000..e90ea25
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/MWMMessageConstraintDebugConfig.java
@@ -0,0 +1,43 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.giraph.debugger.examples.mwm;
+
+import org.apache.giraph.debugger.DebugConfig;
+import org.apache.hadoop.io.DoubleWritable;
+import org.apache.hadoop.io.LongWritable;
+
+/**
+ * DebugConfig for checking message constraints of max weight matching.
+ */
+public class MWMMessageConstraintDebugConfig
+  extends
+  DebugConfig<LongWritable, VertexValue, DoubleWritable, LongWritable,
+  LongWritable> {
+
+  @Override
+  public boolean shouldCheckMessageIntegrity() {
+    return true;
+  }
+
+  @Override
+  public boolean isMessageCorrect(LongWritable srcId, LongWritable dstId,
+    LongWritable message, long superstepNo) {
+    return message.get() == srcId.get();
+  }
+
+}

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/MWMVertexValueConstraintDebugConfig.java
----------------------------------------------------------------------
diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/MWMVertexValueConstraintDebugConfig.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/MWMVertexValueConstraintDebugConfig.java
new file mode 100644
index 0000000..75cdc1b
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/MWMVertexValueConstraintDebugConfig.java
@@ -0,0 +1,43 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.giraph.debugger.examples.mwm;
+
+import org.apache.giraph.debugger.DebugConfig;
+import org.apache.hadoop.io.DoubleWritable;
+import org.apache.hadoop.io.LongWritable;
+
+/**
+ * DebugConfig for checking vertex value constraint for max weight matching.
+ */
+public class MWMVertexValueConstraintDebugConfig
+  extends
+  DebugConfig<LongWritable, VertexValue, DoubleWritable, LongWritable,
+  LongWritable> {
+
+  @Override
+  public boolean shouldCheckVertexValueIntegrity() {
+    return true;
+  }
+
+  @Override
+  public boolean isVertexValueCorrect(LongWritable vertexId,
+    VertexValue value) {
+    return value.getMatchedID() != vertexId.get();
+  }
+
+}

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/VertexValue.java
----------------------------------------------------------------------
diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/VertexValue.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/VertexValue.java
new file mode 100644
index 0000000..2a07b83
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/VertexValue.java
@@ -0,0 +1,89 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.giraph.debugger.examples.mwm;
+
+import java.io.DataInput;
+import java.io.DataOutput;
+import java.io.IOException;
+
+import org.apache.hadoop.io.Writable;
+
+/**
+ * Vertex value for MWM.
+ */
+public class VertexValue implements Writable {
+
+  /**
+   * A constant to store for the matchedID fields of unmatched vertices.
+   */
+  public static final long NOT_MATCHED_ID = -1;
+
+  /**
+   * Id of the matched vertex with this.
+   */
+  private long matchedID;
+  /**
+   * Whether the vertex has been already matched.
+   */
+  private boolean isMatched;
+
+  /**
+   * Default constructor.
+   */
+  public VertexValue() {
+    this.setMatchedID(NOT_MATCHED_ID);
+    this.setMatched(false);
+  }
+
+  public long getMatchedID() {
+    return matchedID;
+  }
+
+  public void setMatchedID(long matchedID) {
+    this.matchedID = matchedID;
+  }
+
+  public boolean isMatched() {
+    return isMatched;
+  }
+
+  public void setMatched(boolean isMatched) {
+    this.isMatched = isMatched;
+  }
+  @Override
+  public void readFields(DataInput in) throws IOException {
+    setMatchedID(in.readLong());
+    setMatched(in.readBoolean());
+  }
+
+  @Override
+  public void write(DataOutput out) throws IOException {
+    out.writeLong(getMatchedID());
+    out.writeBoolean(isMatched());
+  }
+
+  @Override
+  public String toString() {
+    StringBuilder sb = new StringBuilder();
+    sb.append("matchedID=");
+    sb.append(getMatchedID() == NOT_MATCHED_ID ? "?" : getMatchedID());
+    sb.append("\tisMatched=" + isMatched());
+    return sb.toString();
+  }
+
+}

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/package-info.java
----------------------------------------------------------------------
diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/package-info.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/package-info.java
new file mode 100644
index 0000000..08b2e57
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/mwm/package-info.java
@@ -0,0 +1,26 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * This is the Giraph implementation of an approximate maximum weight matching
+ * algorithm. It is used to demonstrate that Graft can help users find problems
+ * in their input graphs. In this case, if there are asymmetric weigths on
+ * the weights of the input graph, then this algorithm will get into an
+ * infinite loop.
+ */
+package org.apache.giraph.debugger.examples.mwm;

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/package-info.java
----------------------------------------------------------------------
diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/package-info.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/package-info.java
new file mode 100644
index 0000000..a4aa81e
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/package-info.java
@@ -0,0 +1,23 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Giraph I/O formats for the buggy example Giraph programs to be debugged
+ * with Graft.
+ */
+package org.apache.giraph.debugger.examples;

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/pagerank/SimplePageRankComputation.java
----------------------------------------------------------------------
diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/pagerank/SimplePageRankComputation.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/pagerank/SimplePageRankComputation.java
new file mode 100644
index 0000000..491b9c1
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/pagerank/SimplePageRankComputation.java
@@ -0,0 +1,94 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.giraph.debugger.examples.pagerank;
+
+import java.io.IOException;
+
+import org.apache.giraph.comm.WorkerClientRequestProcessor;
+import org.apache.giraph.graph.BasicComputation;
+import org.apache.giraph.graph.GraphState;
+import org.apache.giraph.graph.GraphTaskManager;
+import org.apache.giraph.graph.Vertex;
+import org.apache.giraph.worker.WorkerContext;
+import org.apache.giraph.worker.WorkerGlobalCommUsage;
+import org.apache.hadoop.io.DoubleWritable;
+import org.apache.hadoop.io.LongWritable;
+import org.apache.hadoop.io.NullWritable;
+import org.apache.log4j.Logger;
+
+/**
+ * Simple PageRank implementation in Giraph to be easily run with Graft.
+ */
+public class SimplePageRankComputation extends
+  BasicComputation<LongWritable, DoubleWritable, NullWritable, DoubleWritable> {
+
+  /** Sum aggregator name */
+  public static final String SUM_AGG = "sum";
+  /** Min aggregator name */
+  public static final String MIN_AGG = "min";
+  /** Max aggregator name */
+  public static final String MAX_AGG = "max";
+  /** Number of supersteps for this test */
+  private static int MAX_SUPERSTEPS = 10;
+  /** Logger */
+  private static final Logger LOG = Logger
+    .getLogger(SimplePageRankComputation.class);
+
+  @Override
+  public void initialize(
+    GraphState graphState,
+    WorkerClientRequestProcessor<LongWritable, DoubleWritable, NullWritable>
+    workerClientRequestProcessor,
+    GraphTaskManager<LongWritable, DoubleWritable, NullWritable>
+    graphTaskManager,
+    WorkerGlobalCommUsage workerGlobalCommUsage, WorkerContext workerContext) {
+    MAX_SUPERSTEPS = workerContext.getConf().getInt(
+      getClass().getName() + ".maxSupersteps", 10);
+    super.initialize(graphState, workerClientRequestProcessor,
+      graphTaskManager, workerGlobalCommUsage, workerContext);
+  }
+
+  @Override
+  public void compute(
+    Vertex<LongWritable, DoubleWritable, NullWritable> vertex,
+    Iterable<DoubleWritable> messages) throws IOException {
+    if (getSuperstep() >= 1) {
+      double sum = 0;
+      for (DoubleWritable message : messages) {
+        sum += message.get();
+      }
+      DoubleWritable vertexValue = new DoubleWritable(
+        (0.15f / getTotalNumVertices()) + 0.85f * sum);
+      vertex.setValue(vertexValue);
+      aggregate(MAX_AGG, vertexValue);
+      aggregate(MIN_AGG, vertexValue);
+      aggregate(SUM_AGG, new LongWritable(1));
+      // LOG.info(vertex.getId() + ": PageRank=" + vertexValue + " max=" +
+      // getAggregatedValue(MAX_AGG) + " min=" + getAggregatedValue(MIN_AGG));
+    }
+
+    if (getSuperstep() < MAX_SUPERSTEPS) {
+      long edges = vertex.getNumEdges();
+      sendMessageToAllEdges(vertex, new DoubleWritable(vertex.getValue().get() /
+        edges));
+    } else {
+      vertex.voteToHalt();
+    }
+  }
+
+}

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/pagerank/SimplePageRankMasterCompute.java
----------------------------------------------------------------------
diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/pagerank/SimplePageRankMasterCompute.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/pagerank/SimplePageRankMasterCompute.java
new file mode 100644
index 0000000..a4890ab
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/pagerank/SimplePageRankMasterCompute.java
@@ -0,0 +1,41 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.giraph.debugger.examples.pagerank;
+
+import org.apache.giraph.aggregators.DoubleMaxAggregator;
+import org.apache.giraph.aggregators.DoubleMinAggregator;
+import org.apache.giraph.aggregators.LongSumAggregator;
+import org.apache.giraph.master.DefaultMasterCompute;
+
+/**
+ * Master compute associated with {@link SimplePageRankComputation}.
+ * It registers required aggregators.
+ */
+public class SimplePageRankMasterCompute extends
+    DefaultMasterCompute {
+  @Override
+  public void initialize() throws InstantiationException,
+      IllegalAccessException {
+    registerAggregator(SimplePageRankComputation.SUM_AGG,
+      LongSumAggregator.class);
+    registerPersistentAggregator(SimplePageRankComputation.MIN_AGG,
+      DoubleMinAggregator.class);
+    registerPersistentAggregator(SimplePageRankComputation.MAX_AGG,
+      DoubleMaxAggregator.class);
+  }
+}

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/pagerank/package-info.java
----------------------------------------------------------------------
diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/pagerank/package-info.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/pagerank/package-info.java
new file mode 100644
index 0000000..0209586
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/pagerank/package-info.java
@@ -0,0 +1,22 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Simple PageRank implementation in Giraph to be easily run with Graft.
+ */
+package org.apache.giraph.debugger.examples.pagerank;

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/randomwalk/RandomWalkComputation.java
----------------------------------------------------------------------
diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/randomwalk/RandomWalkComputation.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/randomwalk/RandomWalkComputation.java
new file mode 100644
index 0000000..c39d314
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/randomwalk/RandomWalkComputation.java
@@ -0,0 +1,145 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.giraph.debugger.examples.randomwalk;
+
+import java.io.IOException;
+import java.util.Random;
+
+import org.apache.giraph.comm.WorkerClientRequestProcessor;
+import org.apache.giraph.edge.Edge;
+import org.apache.giraph.graph.BasicComputation;
+import org.apache.giraph.graph.GraphState;
+import org.apache.giraph.graph.GraphTaskManager;
+import org.apache.giraph.graph.Vertex;
+import org.apache.giraph.worker.WorkerContext;
+import org.apache.giraph.worker.WorkerGlobalCommUsage;
+import org.apache.hadoop.io.IntWritable;
+import org.apache.hadoop.io.LongWritable;
+import org.apache.hadoop.io.NullWritable;
+
+/**
+ * Random walk implementation in Giraph with short-overflow bugs.
+ */
+public class RandomWalkComputation extends
+  BasicComputation<LongWritable, IntWritable, NullWritable, IntWritable> {
+
+  /**
+   * Default number of initial walkers.
+   */
+  private static final int DEFAULT_NUM_WALKERS = 100;
+  /**
+   * Default length of the random walk.
+   */
+  private static final int DEFAULT_LENGTH_OF_WALK = 20;
+
+  /**
+   * Array for storing the number of walkers for each neighbor of a vertex.
+   */
+  private short[] messagesToNeighbors = new short[2];
+  /**
+   * Initial number of walkers.
+   */
+  private int initialNumWalkers;
+  /**
+   * Length of the random walk.
+   */
+  private int lengthOfWalk;
+
+  @Override
+  public void initialize(
+    GraphState graphState,
+    WorkerClientRequestProcessor<LongWritable, IntWritable, NullWritable>
+    workerClientRequestProcessor,
+    GraphTaskManager<LongWritable, IntWritable, NullWritable> graphTaskManager,
+    WorkerGlobalCommUsage workerGlobalCommUsage, WorkerContext workerContext) {
+    super.initialize(graphState, workerClientRequestProcessor,
+      graphTaskManager, workerGlobalCommUsage, workerContext);
+
+    initialNumWalkers = getConf().getInt(
+      getClass().getName() + ".initialNumWalkers", DEFAULT_NUM_WALKERS);
+    lengthOfWalk = getConf().getInt(getClass().getName() + ".walkLength",
+      DEFAULT_LENGTH_OF_WALK);
+  }
+
+  @Override
+  public void compute(Vertex<LongWritable, IntWritable, NullWritable> vertex,
+    Iterable<IntWritable> messages) throws IOException {
+    // Halt after the walk reaches a certain length.
+    if (getSuperstep() > lengthOfWalk) {
+      vertex.voteToHalt();
+      return;
+    }
+    short numWalkersHere = 0;
+    if (getSuperstep() == 0) {
+      // At the first superstep, start from an initial number of walkers.
+      numWalkersHere += initialNumWalkers;
+    } else {
+      // Otherwise, count the number of walkers arrived at this vertex.
+      for (IntWritable messageValue : messages) {
+        numWalkersHere += messageValue.get();
+      }
+    }
+    vertex.setValue(new IntWritable(numWalkersHere));
+    moveWalkersToNeighbors(numWalkersHere, vertex);
+  }
+
+  /**
+   * Move walkers to neighbors by sending messages.
+   *
+   * @param numMessagesToSend total number of walkers to send out
+   * @param vertex the vertex sending messages
+   */
+  private void moveWalkersToNeighbors(int numMessagesToSend,
+    Vertex<LongWritable, IntWritable, NullWritable> vertex) {
+    Iterable<Edge<LongWritable, NullWritable>> edges = vertex.getEdges();
+    int neighborsLength = vertex.getNumEdges();
+    if (messagesToNeighbors.length < neighborsLength) {
+      messagesToNeighbors = new short[neighborsLength];
+    } else {
+      for (int i = 0; i < neighborsLength; ++i) {
+        messagesToNeighbors[i] = 0;
+      }
+    }
+    Random random = new Random();
+    if (neighborsLength == 0) {
+      // When there's no out-edge, let each walker jump to a random vertex in
+      // the graph.
+      for (int i = 0; i < numMessagesToSend; ++i) {
+        sendMessage(
+          new LongWritable(random.nextInt((int) getTotalNumVertices())),
+          new IntWritable(1));
+      }
+    } else {
+      // Otherwise, distribute the walkers on this vertex to each neighbor.
+      for (int i = 0; i < numMessagesToSend; ++i) {
+        int neighborIdIndex = random.nextInt(neighborsLength);
+        messagesToNeighbors[neighborIdIndex] += 1;
+      }
+      // Then, send out messages containing the number of walkers.
+      int i = 0;
+      for (Edge<LongWritable, NullWritable> edge : edges) {
+        if (messagesToNeighbors[i] != 0) {
+          sendMessage(edge.getTargetVertexId(), new IntWritable(
+            messagesToNeighbors[i]));
+        }
+        i++;
+      }
+    }
+  }
+
+}

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/randomwalk/RandomWalkDebugConfig.java
----------------------------------------------------------------------
diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/randomwalk/RandomWalkDebugConfig.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/randomwalk/RandomWalkDebugConfig.java
new file mode 100644
index 0000000..2fff99d
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/randomwalk/RandomWalkDebugConfig.java
@@ -0,0 +1,55 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.giraph.debugger.examples.randomwalk;
+
+import org.apache.giraph.debugger.DebugConfig;
+import org.apache.hadoop.io.IntWritable;
+import org.apache.hadoop.io.LongWritable;
+import org.apache.hadoop.io.NullWritable;
+
+/**
+ * DebugConfig for random walk algorithm.
+ */
+public class RandomWalkDebugConfig
+  extends
+  DebugConfig<LongWritable, IntWritable, NullWritable, IntWritable,
+  IntWritable> {
+
+  @Override
+  public boolean shouldCheckVertexValueIntegrity() {
+    return true;
+  }
+
+  @Override
+  public boolean isVertexValueCorrect(LongWritable vertexId,
+    IntWritable value) {
+    return value.get() > 0;
+  }
+
+  @Override
+  public boolean shouldCheckMessageIntegrity() {
+    return true;
+  }
+
+  @Override
+  public boolean isMessageCorrect(LongWritable srcId, LongWritable dstId,
+    IntWritable message, long superstepNo) {
+    return message.get() > 0;
+  }
+
+}

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/randomwalk/RandomWalkMessageConstraintDebugConfig.java
----------------------------------------------------------------------
diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/randomwalk/RandomWalkMessageConstraintDebugConfig.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/randomwalk/RandomWalkMessageConstraintDebugConfig.java
new file mode 100644
index 0000000..4d47538
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/randomwalk/RandomWalkMessageConstraintDebugConfig.java
@@ -0,0 +1,56 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.giraph.debugger.examples.randomwalk;
+
+import org.apache.giraph.debugger.DebugConfig;
+import org.apache.giraph.graph.Vertex;
+import org.apache.hadoop.io.IntWritable;
+import org.apache.hadoop.io.LongWritable;
+import org.apache.hadoop.io.NullWritable;
+
+/**
+ * DebugConfig for checking message constraint in random walk implementation.
+ */
+public class RandomWalkMessageConstraintDebugConfig
+  extends
+  DebugConfig<LongWritable, IntWritable, NullWritable, IntWritable,
+  IntWritable> {
+
+  @Override
+  public boolean shouldCatchExceptions() {
+    return false;
+  }
+
+  @Override
+  public boolean shouldDebugVertex(
+    Vertex<LongWritable, IntWritable, NullWritable> vertex, long superstepNo) {
+    return false;
+  }
+
+  @Override
+  public boolean shouldCheckMessageIntegrity() {
+    return true;
+  }
+
+  @Override
+  public boolean isMessageCorrect(LongWritable srcId, LongWritable dstId,
+    IntWritable message, long superstepNo) {
+    return message.get() > 0;
+  }
+
+}

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/randomwalk/RandomWalkVertexValueConstraintDebugConfig.java
----------------------------------------------------------------------
diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/randomwalk/RandomWalkVertexValueConstraintDebugConfig.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/randomwalk/RandomWalkVertexValueConstraintDebugConfig.java
new file mode 100644
index 0000000..7678b12
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/randomwalk/RandomWalkVertexValueConstraintDebugConfig.java
@@ -0,0 +1,57 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.giraph.debugger.examples.randomwalk;
+
+import org.apache.giraph.debugger.DebugConfig;
+import org.apache.giraph.graph.Vertex;
+import org.apache.hadoop.io.IntWritable;
+import org.apache.hadoop.io.LongWritable;
+import org.apache.hadoop.io.NullWritable;
+
+/**
+ * DebugConfig for checking vertex value constraints of random walk
+ * implementation.
+ */
+public class RandomWalkVertexValueConstraintDebugConfig
+  extends
+  DebugConfig<LongWritable, IntWritable, NullWritable, IntWritable,
+  IntWritable> {
+
+  @Override
+  public boolean shouldCatchExceptions() {
+    return false;
+  }
+
+  @Override
+  public boolean shouldDebugVertex(
+    Vertex<LongWritable, IntWritable, NullWritable> vertex, long superstepNo) {
+    return false;
+  }
+
+  @Override
+  public boolean shouldCheckVertexValueIntegrity() {
+    return true;
+  }
+
+  @Override
+  public boolean isVertexValueCorrect(LongWritable vertexId, IntWritable
+    value) {
+    return value.get() >= 0;
+  }
+
+}

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/randomwalk/package-info.java
----------------------------------------------------------------------
diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/randomwalk/package-info.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/randomwalk/package-info.java
new file mode 100644
index 0000000..a9e330d
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/randomwalk/package-info.java
@@ -0,0 +1,22 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Example Giraph random walk algorithm.
+ */
+package org.apache.giraph.debugger.examples.randomwalk;

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/simpledebug/BuggySimpleShortestPathsComputation.java
----------------------------------------------------------------------
diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/simpledebug/BuggySimpleShortestPathsComputation.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/simpledebug/BuggySimpleShortestPathsComputation.java
new file mode 100644
index 0000000..0a1d909
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/simpledebug/BuggySimpleShortestPathsComputation.java
@@ -0,0 +1,106 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.giraph.debugger.examples.simpledebug;
+
+import java.io.IOException;
+
+import org.apache.giraph.Algorithm;
+import org.apache.giraph.conf.LongConfOption;
+import org.apache.giraph.edge.Edge;
+import org.apache.giraph.graph.BasicComputation;
+import org.apache.giraph.graph.Vertex;
+import org.apache.hadoop.io.DoubleWritable;
+import org.apache.hadoop.io.FloatWritable;
+import org.apache.hadoop.io.LongWritable;
+import org.apache.log4j.Logger;
+
+/**
+ * Debug version of SimpleShortestPathsComputation.
+ */
+@Algorithm(name = "Shortest paths", description = "Finds all shortest paths" +
+    "from a selected vertex")
+public class BuggySimpleShortestPathsComputation extends BasicComputation<
+  LongWritable, DoubleWritable, FloatWritable, DoubleWritable> {
+
+  /** The shortest paths id */
+  public static final LongConfOption SOURCE_ID = new LongConfOption(
+    "SimpleShortestPathsVertex.sourceId", 1, "The shortest paths id");
+  /** Class logger */
+  private static final Logger LOG = Logger
+    .getLogger(BuggySimpleShortestPathsComputation.class);
+
+  /**
+   * Is this vertex the source id?
+   *
+   * @param vertex
+   *          Vertex
+   * @return True if the source id
+   */
+  private boolean isSource(Vertex<LongWritable, ?, ?> vertex) {
+    return vertex.getId().get() == SOURCE_ID.get(getConf());
+  }
+
+  @Override
+  public void compute(
+    Vertex<LongWritable, DoubleWritable, FloatWritable> vertex,
+    Iterable<DoubleWritable> messages) throws IOException {
+    // We do a dummy read of the aggregator below because for now we only
+    // intercept an aggregator
+    // if at least one vertex reads it.
+    LongWritable aggregatedValue = getAggregatedValue(
+      SimpleShortestPathsMaster.NV_DISTANCE_LESS_THAN_THREE_AGGREGATOR);
+    if (aggregatedValue != null) {
+      System.out.print("NV_DISTANCE_LESS_THAN_THREE_AGGREGATOR: " +
+        aggregatedValue.get() + "\n");
+    }
+    if (getSuperstep() == 0) {
+      vertex.setValue(new DoubleWritable(isSource(vertex) ? 0d :
+        Double.MAX_VALUE));
+    }
+    double previousValue = vertex.getValue().get();
+    double minDist = previousValue;
+    for (DoubleWritable message : messages) {
+      minDist = Math.min(minDist, message.get());
+    }
+    if (LOG.isDebugEnabled()) {
+      LOG.debug("Vertex " + vertex.getId() + " got minDist = " + minDist +
+        " vertex value = " + vertex.getValue());
+    }
+    if (minDist < vertex.getValue().get() || getSuperstep() == 0 &&
+      minDist == 0) {
+      vertex.setValue(new DoubleWritable(minDist));
+      for (Edge<LongWritable, FloatWritable> edge : vertex.getEdges()) {
+        double distance = minDist + edge.getValue().get();
+        if (LOG.isDebugEnabled()) {
+          LOG.debug("Vertex " + vertex.getId() + " sent to " +
+            edge.getTargetVertexId() + " = " + distance);
+        }
+        // INTENTIONAL BUG:Instead of sending the distance (i.e. by adding edge
+        // values),
+        // we send minDist, which is the vertex value.
+        sendMessage(edge.getTargetVertexId(), new DoubleWritable(minDist));
+      }
+    }
+    if (previousValue > 3 && minDist <= 3) {
+      aggregate(
+        SimpleShortestPathsMaster.NV_DISTANCE_LESS_THAN_THREE_AGGREGATOR,
+        new LongWritable(1));
+    }
+    vertex.voteToHalt();
+  }
+}

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/simpledebug/SimpleShortestPathsDebugConfig.java
----------------------------------------------------------------------
diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/simpledebug/SimpleShortestPathsDebugConfig.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/simpledebug/SimpleShortestPathsDebugConfig.java
new file mode 100644
index 0000000..f2006e6
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/simpledebug/SimpleShortestPathsDebugConfig.java
@@ -0,0 +1,43 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.giraph.debugger.examples.simpledebug;
+
+import org.apache.giraph.debugger.DebugConfig;
+import org.apache.giraph.graph.Vertex;
+import org.apache.hadoop.io.DoubleWritable;
+import org.apache.hadoop.io.FloatWritable;
+import org.apache.hadoop.io.LongWritable;
+
+/**
+ * Debug configuration file for SimpleShortestPathDebugComputation.
+ */
+public class SimpleShortestPathsDebugConfig extends DebugConfig<LongWritable,
+  DoubleWritable, FloatWritable, DoubleWritable, DoubleWritable> {
+
+  @Override
+  public boolean shouldDebugSuperstep(long superstepNo) {
+    return true;
+  }
+
+  @Override
+  public boolean shouldDebugVertex(
+    Vertex<LongWritable, DoubleWritable, FloatWritable> vertex,
+    long superstepNo) {
+    return true;
+  }
+}

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/simpledebug/SimpleShortestPathsMaster.java
----------------------------------------------------------------------
diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/simpledebug/SimpleShortestPathsMaster.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/simpledebug/SimpleShortestPathsMaster.java
new file mode 100644
index 0000000..e2559cc
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/simpledebug/SimpleShortestPathsMaster.java
@@ -0,0 +1,75 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.giraph.debugger.examples.simpledebug;
+
+import org.apache.giraph.aggregators.LongSumAggregator;
+import org.apache.giraph.debugger.examples.exceptiondebug.BuggySimpleTriangleClosingComputation;
+import org.apache.giraph.graph.Computation;
+import org.apache.giraph.master.DefaultMasterCompute;
+import org.apache.hadoop.io.LongWritable;
+
+/**
+ * Master compute associated with {@link BuggySimpleShortestPathsComputation}.
+ * It handles dangling nodes.
+ */
+public class SimpleShortestPathsMaster extends DefaultMasterCompute {
+
+  /**
+   * Name of the aggregator keeping the number of vertices which have distance
+   * less than three to the source vertex.
+   */
+  public static final String NV_DISTANCE_LESS_THAN_THREE_AGGREGATOR =
+    "nvWithDistanceLessThanThree";
+
+  @SuppressWarnings({ "unchecked", "rawtypes" })
+  @Override
+  public void compute() {
+    System.out.print("Running SimpleShortestPathsMaster.compute. superstep " +
+      getSuperstep() + "\n");
+    LongWritable aggregatorValue = getAggregatedValue(
+      NV_DISTANCE_LESS_THAN_THREE_AGGREGATOR);
+    if (aggregatorValue != null) {
+      System.out.print("At Master.compute() with aggregator: " +
+        aggregatorValue.get() + "\n");
+    }
+    // if (getSuperstep() == 2) {
+    // throw new IllegalArgumentException("DUMMY EXCEPTION FOR TESTING");
+    // }
+
+    // Dummy code for testing Instrumenter analysis
+    if (getSuperstep() == 100000) {
+      // which is extremely less likely to happen,
+      setComputation(BuggySimpleTriangleClosingComputation.class);
+    } else if (getSuperstep() == 200000) {
+      try {
+        setComputation((Class<? extends Computation>) Class.forName(
+          "org.apache.giraph.debugger.examples.integrity." +
+          "ConnectedComponentsActualComputation"));
+      } catch (ClassNotFoundException e) {
+        e.printStackTrace();
+      }
+    }
+  }
+
+  @Override
+  public void initialize() throws InstantiationException,
+    IllegalAccessException {
+    registerPersistentAggregator(NV_DISTANCE_LESS_THAN_THREE_AGGREGATOR,
+      LongSumAggregator.class);
+  }
+}

http://git-wip-us.apache.org/repos/asf/giraph/blob/8675c84a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/simpledebug/package-info.java
----------------------------------------------------------------------
diff --git a/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/simpledebug/package-info.java b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/simpledebug/package-info.java
new file mode 100644
index 0000000..dd3d603
--- /dev/null
+++ b/giraph-debugger/src/main/java/org/apache/giraph/debugger/examples/simpledebug/package-info.java
@@ -0,0 +1,22 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * A simple example Giraph program that can be easily debugged using Graft.
+ */
+package org.apache.giraph.debugger.examples.simpledebug;


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